Chemical Reaction

B

134

ChemicalReactionsChemicalReactions

The energy to launch the Delta II rocket comes from chemicalreactions. This rocket iscarrying a Canadiancommunications satellite.

U N I T

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Unit Task

In the Unit Task, you will carry out a number of chemicalreactions involving substances that contain magnesium.You will identify the types of substances used in thechemical reactions. You will use this knowledge to predictthe results of three different chemical reactions and thentest your predictions by carrying out the reactions.

Essential QuestionWhat role do chemical reactions play in my life at home, atschool, at work, during leisure activities, and in theenvironment?

Chemical change occurs during chemicalreactions.

4.1 Matter and the Periodic Table

4.2 Ions, Molecules, and Compounds

4.3 Chemical Reactions

Acids and bases are important to our health,industries, and environment.

5.1 Acids and Bases

5.2 Neutralization Reactions

Chemical reactions can be grouped accordingto the characteristics of their reactants andproducts.

6.1 Synthesis Reactions and Decomposition Reactions

6.2 Combustion Reactions and Displacement Reactions

DI

DI

DI

Contents

4

5

6

135

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This type of brain scan detects areas that are highly active. It can be used to find which parts of the brain are involved in specificmental tasks.

Lighting the Brain with Chemistry Your brain carries out an incredible number of tasks. As well as beingthe source of all your thoughts, your brain controls your heart rate,breathing, body temperature, and blood pressure. It co-ordinates themovement of your body and processes all the information from yoursenses. These functions depend on electrical impulses and involvemany different chemical reactions.

We still have an incomplete picture of how the brain works. Brainscans, such as the functional magnetic resonance imaging (fMRI) scanshown above, allow us to see which part of a brain is most active duringsome task. For example, a patient might be asked to name an object in aphotograph or to multiply two numbers during the fMRI scan.However, this technology does not allow researchers to see the workingbrain in much detail. Recently, the chemistry of a species of jellyfishthat glows green has been brought together with genetics and the study of the brain to develop a way of lighting up the brains of mice in great detail.

Green fluorescent protein (GFP ) is produced by the jellyfish speciesAequorea victoria, which lives in the Pacific Ocean (see photo on theleft). These jellyfish use a chemical reaction to produce a blue light,which is immediately absorbed by the green fluorescent protein,causing it to glow green.

136 UNIT B Chemical Reactions

Exploring

Individuals of the jellyfish speciesAequorea victoria use a chemicalreaction to produce a blue light.

Green fluorescentprotein from jellyfishis being used to lightup the brains of mice.

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137Exploring

Colouring Brain Activity Recently, researchers have been able to transfer theability of the jellyfish to produce green fluorescentprotein to certain mice. The mice were geneticallyaltered by giving them a special modified version of thegene that produces green fluorescent protein in thejellyfish. The result is that genetically altered mice,which look and behave normally in daylight, have braincells that will glow in up to 90 different colours in bluelight, as shown in the photo on the right. Since eachindividual brain cell is a different colour than the cellbeside it, it now possible to identify individual electricalconnections inside the brains of these mice. This can, inturn, build knowledge that can help us all to have healthybrains all of our lives.

The differerent colours of fluorescent proteins can be usedto detect proteins in the brain, creating a “brainbow.”

B1

How Does Chemistry Improve My Life?

Consider ways in which chemistry and/or knowledgeof chemistry has positive effects in your life. Forexample, new medicines often rely on the synthesisof new chemicals. Chemistry is also at the centre ofthe development of paints and household cleanersthat are less harmful to the environment.

1. In a group, do a two-minute brainstorm. Outlinein a list as many ways as you can think of inwhich chemicals or chemical reactions haveimproved your life or the lives of those aroundyou.

2. Organize your list into examples that improveyour life at home, school, work, and play.

3. Create a mind map or other graphic organizer toshare your ideas with others. You may want touse chart paper or a computer program to createyour graphic organizer.

4. Look at the work of other groups in your class.You may wish to add some of their ideas to yourgraphic organizer.

5. As a class, discuss the question: Why isknowledge of chemistry important to me?

Science, Technology, Society, and the EnvironmentSTSE

Advances in medicine, such as new prescription and non-prescription drugs, depend on chemistry.

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4 Chemical change occurs during chemical reactions.

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Chemical change occurs during chemical reactions. 139

These beautiful Canada Day fireworks are excellentexamples of chemical changes. The colours you seedepend on the chemical elements used.

Skills You Will UseIn this chapter, you will:

• construct molecular models to illustrate the structure ofmolecules in simple chemical reactions and producediagrams of these models

• use an inquiry process to investigate the law of conservation ofmass in a chemical reaction

• plan and conduct an inquiry about chemical change

Concepts You Will LearnIn this chapter, you will:

• analyze safety and environmental issues

• analyze how an understanding of the properties and reactionsof chemicals can be applied to solve environmental challenges

• describe the relationships between chemical formulas,composition, and names of binary compounds

• explain, using the law of conservation of mass and atomictheory, the rationale for balancing chemical equations

• describe the types of evidence that indicate chemical change

• write word equations and balanced chemical equations

• identify and write the formulas for simple compounds

Why It Is ImportantChemical reactions help to keep your body healthy, sustain theenvironment, and provide many of the products you use everyday. They can also cause negative effects on your health and theenvironment.

Determining Importance

Readers often have to decide what information is interesting

and what is important. This textbook includes features to

help you do this. Scan the top of this page, the summary

boxes that start each section of this chapter, and any other

features that help you determine what is important. Create a

web of these features, indicating how each points you

towards important information.

Key Terms

• balanced chemical equation • chemical reaction • ion

• ionic compound • law of conservation of mass

• molecular compound • polyatomic ion

Before Reading

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Ontario’s Chemical Industry and ResearchOntario is a world leader in developing new chemicals and new plasticproducts. Eight of the 10 largest chemical companies in the worldoperate in Ontario. Our chemical companies are centred in three majorregions of the province: the Greater Toronto area, Ontario East, andSarnia (Figure 4.1). Chemical manufacturing in Ontario is theprovince’s third-largest manufacturing industry. In 2008, Ontario’schemical industry employed over 50 000 people and produced productsworth over $22 billion.

An important part of the chemical industry is the manufacture ofplastic and plastic products. Ontario’s plastic manufacturing industryemploys over 80 000 people and has annual sales of over $18 billion.Consider your own connection to plastic. On a typical day, you likelyuse several of the following products that involve plastic somewhere intheir manufacture: music players, televisions, carpeting, paints and dyes(on walls, pencils, table tops), clothing (made from plastic fibres such aspolyester, rayon, and nylon), packaging materials (plastic wrapincluding food wrap), and cellphones (Figure 4.2).

Here is a summary of what youwill learn in this section:

• Matter is composed of atoms,which are composed ofprotons, neutrons, andelectrons.

• In the periodic table, theelements are represented bysymbols and organized byatomic number.

• According to the Bohr-Rutherford atomic model,protons and neutrons are inthe nucleus and electronsoccur in shells around thenucleus.

• Atoms can combine to formnew substances.

Matter and the Periodic Table

Figure 4.1 Close to 40 percent of Canada’s chemical companies are located in the ChemicalValley near Sarnia, Ontario.

4.1

Figure 4.2 The outer case and theelectronic boards of a cellphone areall made of plastic.

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141Chemical change occurs during chemical reactions.

Chemistry researchers employed by industry, universities, or thegovernment look for new ways to solve everyday problems, includingenvironmental issues. For example, scientists at the National ResearchCouncil of Canada Institute for Research in Construction, situated inOttawa, are investigating ways that we can reduce or prevent concreteroads, bridges, and other structures from corroding. Dr. E.K. Yanful atthe University of Western Ontario in London is one of many scientistsstudying new methods to reduce the environmental impact of the wastefrom mining operations (Figure 4.3).

The chemical industry is responsible for ensuring that itmanufactures products and deals with wastes in a responsible andenvironmentally friendly manner. Just as we recycle household itemsthat were once considered waste, chemical industries now try to finduses for the different by-products of their processes rather than simplydisposing of them.

Companies and government agencies carry out monitoring toensure that nothing hazardous escapes or is released frommanufacturing sites. By gradually raising standards and awarenessamong chemical producers and communities, we have greatly decreasedthe negative impacts of industrial production.

B2 Quick Lab

What Do I Know about Chemistry?

In this activity, you will create an individual mind mapfocussed on the question “What do I know aboutchemistry?” This will help you build a foundation fornew learning.

PurposeTo determine what you already know about chemistry

Procedure

1. Use chart paper or a computer graphicsprogram. Start your mind map by writing thequestion “What do I know about chemistry?”

2. Record what you know and what you think youknow about chemicals and chemical reactions onyour mind map.

3. On the sides or back of your mind map, list anyquestions you have about chemistry andchemical reactions.

4. When you have completed your mind map, shareit with a partner. Add your partner’s ideas to yourmap using another colour.

Question

5. Were there any concepts you thought you knewthat you are no longer sure about after workingwith your partner? If so, add these to thequestions on your mind map.

Materials & Equipment• coloured pens/pencils

• chart paper

• computer (optional)

• graphics program (optional)

Figure 4.3 Dr. E.K. Yanful (P.Eng.) isassociate director of the GeotechnicalReseach Centre and professor andchair of the Civil and EnvironmentalEngineering Department at theUniversity of Western Ontario.

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Words IndicateImportant Ideas

In any sentence, there are contentwords — usually nouns or verbs —

that carry the real meaning of the

sentence, and function words —

pronouns, prepositions, articles —

that create the sentence structure

but carry little meaning. Read

several sentences, and find the

content words that tell you what is

important.

During Reading MatterYou and every object around you are made of matter. Matter isanything that has mass and takes up space (has volume). Matter doesnot include any form of energy, such as light, heat, and sound. Thereare millions of forms of matter that have been discovered orsynthesized. To understand more about matter, many substances havebeen classified according to shared properties.

Physical Properties of Matter A physical property is a property that describes the physicalappearance and composition of a substance. Table 4.1 lists commonphysical properties used for classifying substances.


Figure 4.4 Crystals of the mineralquartz. The formation of crystals is aphysical property that can be used toclassify substances.

Physical Property Description

boiling point or condensation point temperature of boiling or condensing

melting point or freezing point temperature of melting or freezing

malleability ability to be beaten or rolled into sheets withoutcrumbling

ductility ability to be stretched without breaking

colour colour

state solid, liquid, gas

solubility ability to dissolve in a liquid

crystal formation crystalline appearance (Figure 4.4)

conductivity ability to conduct heat or electricity

Table 4.1 Common Physical Properties Used for Classifying Substances

Chemical Property Description

ability to burn combustion (flame, heat, light)

flash point lowest temperature at which a flammable liquidwill ignite in air

behaviour in air tendency to degrade, react, or tarnish

reaction with water tendency to corrode or dissolve

reaction to heating tendency to melt or decompose

Table 4.2 Common Chemical Properties Used for Classifying Substances

Chemical Properties of Matter A chemical property is a property that describes the ability of asubstance to change into a new substance or substances. Table 4.2 listssome common chemical properties used for classifying substances.

Suggested Activity •B3 Inquiry Activity on page 151

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matter

heterogeneousmixtures

homogeneousmixtures

solutionssuspensionsmechanicalmixtures

mixtures

elements

pure substances

compounds

Pure Substances and MixturesAll forms of matter can be classified as either a pure substance or amixture, based on their physical and chemical properties. These twoclasses can then be further divided, as shown in Figure 4.5.

A pure substance is made up of only one kind of matter and has aunique set of properties, such as colour, hardness, melting point, andconductivity. A pure substance is either an element or a compound.

• An element is a substance that cannot be broken down into anysimpler substance by chemical means. Iron, oxygen, and neon areexamples of elements.

• A compound is a pure substance that is made from two or moreelements that are combined together chemically. For example,methane (CH4) is a compound containing the elements carbonand hydrogen.

A mixture is a combination of pure substances. The proportions ofthe pure substances in a mixture can vary, so the properties of themixture vary as well.

• A homogeneous mixture is a mixture that looks the samethroughout and the separate components are not visible.Solutions are homogeneous mixtures. For example, iced tea is asolution of sugar and other substances dissolved in water (Figure 4.6(a)).

• A heterogeneous mixture is one in which different parts of themixture are visible. In a suspension, a cloudy mixture is formedin which tiny particles of one substance are held within anothersubstance. Salad dressing is an example of a suspension (Figure4.6(b)). Another kind of mixture, called a mechanical mixture,may contain several solids combined together, such as in achocolate-chip cookie.


Figure 4.6 (a) Iced tea is a solution ofsugar and other substances in water.It is homogeneous. (b) Salad dressingis a suspension of oil in vinegar. It isheterogeneous.

WORDS MATTER

The prefix “homo-” means same. Theprefix “hetero-” means different.Figure 4.5

The classification of matter

(a)

(b)

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Matter Is Made of AtomsAll matter is made up of tiny particles called atoms. An atom is thesmallest part of an element that has all the element’s properties. Forexample, gold and silver are both elements. Atoms of gold are similar toeach other but different from atoms of silver, giving each elementdifferent properties, such as colour.

Atomic TheoryAtomic theory is the study of the nature of atoms and how atomscombine to form all types of matter. Each element has its own uniquekind of atom. Atoms of different elements vary in mass, volume, andreactivity. For example, gold atoms are heavier and less reactive thansilver atoms.

Atoms are not the smallest particles in matter. Subatomic particlescombine together to form atoms. Three subatomic particles (protons,neutrons, and electrons) combine in different combinations to make allknown atoms.

Electrons and protons have an electric charge. Protons have apositive charge of 1+. Electrons have a negative charge of 1�. Anyparticle with no charge is called neutral. Neutrons are neutral. Theycan also be said to have a charge of 0.

Like all forms of matter, subatomic particles have mass. The massesof protons and neutrons are almost 2000 times greater than the mass ofelectrons.

Inside an atom, protons and neutrons are in a tiny central corecalled a nucleus (Figure 4.7). The protons and neutrons are heldtogether by a strong force that exists only in the nucleus. Surroundingthe nucleus, and more than 10 000 times larger than it, are a series ofcloud-like energy levels called shells. These shells are occupied byelectrons (Table 4.3).


WORDS MATTER

The word “subatomic” is derivedfrom the Latin sub, meaning under orsmaller than, and the Greek atomos,meaning indivisible.

The word “electron” comes fromelektron, the Greek word for amber.

cloud of electrons

nucleus

Figure 4.7 Atoms are composed of atiny, massive nucleus, surrounded bylarge cloud-like energy levelscontaining electrons.

Name SymbolRelativeMass Charge

Location

Proton p 1836 1+ nucleus

Neutron n 1837 0 nucleus

Electron e 1 1� in shells surrounding the nucleus

Table 4.3 Properties of Subatomic Particles

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Sulphur — A Typical AtomSulphur is an element. Elemental sulphur is a yellow non-metal (Figure 4.8). The basic arrangement of the nucleus and electrons in asulphur atom is typical of all atoms. The atoms of every element have aunique number of protons. Only sulphur atoms have 16 protons.

Figure 4.9(a) is a Bohr diagram of a sulphur atom. A Bohr diagramis an illustration of an atom that shows the arrangement and number ofelectrons in each shell. A Bohr diagram is named after Niels Bohr, theDanish physicist who made important contributions to the developmentof atomic theory (Figure 4.10). Figure 4.9(b) illustrates the nucleus ofthe sulphur atom. In reality, the nucleus is thousands of times smallerthan the part of the atom occupied by electrons.

Sulphur atoms have certain properties representative of all atoms:

• Sulphur atoms always have 16 protons. Each different element has its own unique number of protons. Later in this section, a chart called the periodic table will be used to determine the number of protons in any given element.

• Sulphur atoms have 16 electrons, equal to the number of protons. In all atoms, the number of electrons is equal to the number of protons.

• The electrons surround the nucleus in shells. Each shell has a specific energy level. The innermost shell can hold twoelectrons at most. The next two shells can hold up to eightelectrons each. The outermost shell of an atom is called thevalence shell. In a sulphur atom, the valence shell holds sixelectrons. The electrons in the valence shell of an atom are called valence electrons.


Figure 4.8 Sulphur is a yellow, non-metallic element. Sulphur hasmany uses, such as in makingsulphuric acid. Sulphuric acid is usedin vehicle batteries.

neutron proton

sulphur atom

nucleus

valence shell

valence electron

inner shells

inner electron

Figure 4.9 (a) A Bohr diagram of sulphur, which contains 16 protons and 16 electrons. The number of neutrons varies between sulphur atoms. (b) A diagram of the nucleus of asulphur atom

Figure 4.10 Niels Bohr proposed amodel of the atom in 1913, when hewas 28 years old. In 1922, hereceived the Nobel Prize in physics forthis work.

(a) (b)

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The Periodic Table of ElementsFigure 4.11 on the facing page shows the periodic table of the elements.The periodic table contains a standard set of symbols to represent theelements, laid out in a specific pattern. It is based on the organizationdeveloped by Dmitri Mendeleev in 1869 (Figure 4.12). The periodictable has the following characteristics:

• The horizontal rows of the periodic table are called periods.

• The vertical columns are called families (or groups). Elementsin the same family in the periodic table have similar physical andchemical properties.

• Metals are on the left and in the centre of the table. Metals areelements with the following properties: they are good conductorsof heat and electricity, they are ductile and malleable, they areshiny and usually silver coloured, and all but one are solids atroom temperature. Mercury is a metal, but it is liquid at roomtemperature.

• Non-metals are located on the right-hand side of the table. Non-metals are elements that share these properties: they arenot metals, and they generally are poor conductors of heat andelectricity. At room temperature, some non-metals are solids,some are gases, and one, bromine, is a liquid.

• Metals are separated from non-metals by a staircase of elementscalled the metalloids. Metalloids are elements with propertiesintermediate between the properties of metals and non-metals.


Figure 4.12 Dmitri Mendeleev wasthe first person to create a table thatorganized all the elements logically,including those that wereundiscovered at the time.

Learning Checkpoint

1. List the name and charge of three subatomic particles.

2. (a) Which two subatomic particles exist together in the nucleus?

(b) Which subatomic particle is located in shells surrounding the nucleus?

3. The atoms of each element have a unique number of which subatomic

particle?

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ts d

ispl

ays

the

elem

ents

and

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thei

r pr

oper

ties

in a

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gani

zed

char

t.

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Four Common Chemical FamiliesFour common chemical families are known both by their groupnumber and special names. The location of these families in theperiodic table is shown in Figure 4.13. As in all chemical families,elements within each family share similar chemical and physicalproperties.

• alkali metals (group 1): soft, silver-grey metals that react easilywith water and with oxygen in the air (Figure 4.14). Note thathydrogen is not an alkali metal.

• alkaline earth metals (group 2): silver-grey metals that areharder and less reactive than group 1 metals. A reactive atomcombines easily with other atoms.

• halogens (group 17): coloured non-metals that are very reactive

• noble gases (group 18): non-metals that are colourless, odourlessgases and very unreactive. An unreactive atom does not combineeasily with other atoms.

148

H1

Li3

Na11

K19

Rb37

Cs55

Fr87

Be4

Mg12

Ca20

Sr38

Ba56

Ra88

F9

Cl17

Br35

I53

At85

He2

Ne10

Ar18

Kr36

Xe54

Rn86

AlkalineEarthMetals Halogens

Groups3 - 16

NobleGases

AlkaliMetals

Figure 4.13 Four families in theperiodic table are known by both agroup number and a special name.

Figure 4.14 Three alkali metals

Learning Checkpoint

Refer to the periodic table (Figure 4.11, page 147) to answer questions 1 to 5.

1. What are the names of the eight elements in period 2 on the periodic table,

going from left to right?

2. Other than carbon, what elements are in group 14 on the periodic table?

3. For each of the following, identify the element from the description of its

location on the periodic table:

(a) period 1, group 18 (c) period 4, group 17

(b) period 3, group 2 (d) period 2, group 16

4. (a) Which period contains the highest number of non-metals?

(b) What are the names of the non-metallic elements in this period?

5. (a) Which group contains the highest number of non-metals?

(b) List three properties that are common to all the elements in this family.

UNIT B Chemical Reactions

Elements on the Periodic TableEach element is represented by a square on the periodic table. Forexample, Figure 4.15 shows the square that represents copper (seeFigure 4.11 on page 147), and Figure 4.16 shows the square thatrepresents fluorine. The information given in the square may varybetween different periodic tables, but it usually includes the name,symbol, atomic number, atomic mass, and ion charge of the element.The last three of these are described on the next page.

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copper63.55

29 2 +1 +Cu


Atomic NumberThe atomic number is the number of protons in an atom of anelement. The atomic number of copper is 29, so an atom of copper has29 protons (Figure 4.15). Also, any atom that has 29 protons is an atomof copper. Since all atoms have an equal numbers of protons andelectrons, an atom of copper has 29 electrons. The lowest atomicnumber is 1, which is the atomic number of the element hydrogen (H).Fluorine has an atomic number of nine, so a fluorine atom has nineprotons (Figure 4.16).

Atomic MassThe atomic mass of an element is a measure of the average mass of anatom of that element. Hydrogen atoms have an atomic mass of about 1,which is the lowest of all the elements. The atomic mass of copper is63.55. This means that the mass of a copper atom is about 64 times themass of a hydrogen atom. As Figure 4.16 shows, the atomic mass offluorine is 19.00. This is about 19 times the mass of a hydrogen atom.

Ion ChargeAn ion is an atom or group of atoms with a negative charge or apositive charge. Atoms of some elements can gain or lose electronsduring chemical change. An atom that gains electrons becomes anegatively charged ion. An atom that loses electrons becomes apositively charged ion.

For example, if an atom of the metal copper loses two electrons, itbecomes a copper ion with an ion charge of 2+. The information on theperiodic table shows that a copper atom can form two different ions,one with an ion charge of 2+ and one with an ion charge of 1+. Incontrast, an atom of the non-metal fluorine can form only one ion withan ion charge of 1–.

Learning Checkpoint

Refer to the periodic table (Figure 4.11 on page 147) to answer questions 1 to 3.

1. Write the name and symbol for elements with the following atomic numbers:

(a) 1 (b) 11 (c) 17 (d) 29 (e) 92

2. By how many times is the atomic mass of each of the following elements

greater than the atomic mass of hydrogen?

(a) helium (b) carbon (c) oxygen (d) lead (e) gold

3. Suppose that atoms of the following elements form ions. Write all the possible

ion charges that the ion(s) could have.

(a) lithium (b) oxygen (c) iodine (d) nickel

Figure 4.15 Information from theperiodic table about an atom ofcopper (Cu)

F9 1-

19.00fluorine

Figure 4.16 Information on theperiodic table shows that an atom ofthe element fluorine (F) has 9protons, 9 electrons, is about 19 times heavier than an atom ofhydrogen, and forms an ion with acharge of 1–.

atomicnumber

ioncharges

atomicmass

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Patterns in the Arrangements of ElectronsFigure 4.17 shows Bohr diagrams for the first 20 elements of theperiodic table. As you examine the Bohr diagrams, look carefully at the electrons in the outer shells. Recall that the outermost electrons are called valence electrons, and the shells they occupy are calledvalence shells.

• The maximum number of electrons in the innermost shell is two. The maximum number of electrons in the next two shells is eight.

• All atoms of elements in the same group have the same numberof valence electrons. For example, all elements in group 1 haveone valence electron.

• All atoms of elements in the noble gas family (group 18) havecompletely full valence shells. In other words, the valence shell ofatoms in this group has the maximum number of electrons. As aresult, atoms of elements in this family are extremely unreactive.


K4

Na3

Li2

H1

1

19

11

3

1

Ca

Mg

Be

2

20

12

4

18

13 14 15 16 17

Al

B

13

5

Si

C

14

6

P

N

15

7

S

O

16

8

Cl

F

17

9

Ar

Ne

He

18

10

2

Figure 4.17 Bohr diagrams of the first 20 elements of the periodic table: The maximumnumber of electrons in the first three shells of an atom follows the pattern 2, 8, 8.

Suggested STSE Activity •B4 Decision-Making Analysis Case Studyon page 152

Learning Checkpoint

Refer to Figure 4.17 to answer questions 1 to 3.

1. For each of the following elements, write the total number of electrons and the

number of valence electrons in one atom.

(a) lithium (b) nitrogen (c) neon (d) silicon (e) calcium

2. What do all elements of the same period (or row) have in common, with

respect to the arrangements of their electrons?

3. Write the name and atomic number of the three elements in Figure 4.17 that

have completely filled valence shells.

There is more than onearrangement of the periodic tableused today. Find some examplesof other ways of representing theperiodic table at ScienceSource.

Take It Further

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151

B3 Inquiry Activity

QuestionWhat changes can you observe when you placecalcium metal in water?

Procedure

1. Place the medium test tube in the test-tube rack,and then fill it with water to a depth of about 3 cm.

2. Light the candle. Light a wooden splint, and bringit near the mouth of the large test tube. Observe.Put the splint out. Record your observations.

3. Obtain a piece of calcium metal. Use tweezers tohandle the calcium metal. Do not touch thecalcium metal with your bare hands.

4. Using the tweezers, place a small piece of calciummetal into the water in the medium test tube.Place the large test tube over the mouth of themedium one, as shown in Figure 4.18. Observewhat happens for 30 s. Record your observations.

5. Use the candle to light a wooden splint.

6. Lift the large test tube off the medium tube,keeping the mouth of the large tube facing down.Keep firm hold of the large test tube and beprepared for a reaction. With the large test tubestill facing down, bring a lit wooden splint near themouth of the large test tube. Observe. Put thesplint out. Record your observations.

7. Examine the inside surface of the large test tube.Using the tweezers, put a piece of blue cobaltchloride paper inside the large test tube. Recordyour observations.

8. Clean up your work area. Make sure to follow yourteacher’s directions for safe disposal of materials.Wash your hands thoroughly.

Analyzing and Interpreting

9. Make a table of the changes you observed whenthe calcium metal was placed into water.

10. What was the purpose of testing the large testtube with a lighted splint in step 2?

11. Blue cobalt chloride paper changes to pink in thepresence of water. Explain what you observed instep 7.

12. What information in section 4.1 helps youinterpret any changes you observed?

Skill Practice

13. Suggest why you must be careful to avoidtouching calcium metal.

Forming Conclusions

14. What evidence do you have that one or more newpure substances was produced?

Water and Calcium

SKILLS YOU WILL USE■ Gathering, organizing, and

recording relevant data frominquiries

■ Interpreting data/information toidentify patterns or relationships

CAUTION• Do not touch the calcium, since it will react with

moisture on your hands.• Tie back any loose hair or clothing.

• medium test tube

• test-tube rack

• water

• candle, in sand on ametal tray

• matches or flame striker

• 2 wooden splints

• calcium metal

• tweezers

• large test tube (must fit over medium testtube)

• blue cobalt chloridepaper

Skills References 1, 2, 6, 9

Materials & Equipment

large test tube

small test tube

watercalcium metal

Figure 4.18 Fit the large test tube over the mouth of the medium one.

Key ActivityD

I

Chemical change occurs during chemical reactions.

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CASE STUDY


SKILLS YOU WILL USE■ Justifying conclusions■ Identifying bias

Ada Lockridge and the Chemical Valley

STSEB4

IssueWhy is knowledge about chemicals and chemicalreactions important to everyone in society?

Background InformationChemicals play an important role in business inOntario. Ontario’s chemical industry directly employsover 50 000 people, who created and sold productsworth over $22 billion in 2008. In addition, almost twodozen manufacturing sectors depend on thechemical industry, including food processing,aerospace, alternative energy, automotive, chemicalmanufacturing, environmental services,pharmaceuticals, and mining. Therefore, thechemical industry has had many positive effects onOntario’s economy.

However, as with many human activities, thechemical industry can have unintended negativeeffects. Ada Lockridge knows this more than mostpeople (Figure 4.19). Lockridge grew up inAamjiwnaang First Nation Reserve near Sarnia,Ontario. Here, 62 different chemical plants make upCanada’s Chemical Valley, which surrounds thereserve. Like many residents of the area, Lockridgefirst ignored the strong smells and occasionalchemical spills and accidents. As the years went byand she had children of her own, Lockridge grewconcerned that there might be negative environmentaleffects from chemicals released from the ChemicalValley.

In 2003, Lockridge learned from biologist MichaelGilbertson that the environment of the reserve hadhigher-than-normal levels of certain chemicals thatcould be hazardous to human health. Some of thesechemicals were known to affect the number of malebabies born. Were these chemicals affecting thehealth of the Aamjiwnaang First Nation community?

To answer that question, Lockridge checked thebirth records for her reserve. The results wereshocking. Between the mid-1990s and 2003, thenumber of male babies had dropped off significantly.

In 2005, in the well-respected journalEnvironmental Health Perspectives, Lockridge and hercolleagues published a paper relating the skewed birthratio to chemicals in the environment.

Analyze and Evaluate

1. Answer the question posed under the heading“Issue.” Support your answer using theinformation in this activity.

2. Web 2.0 Develop your answer as a Wiki, apresentation, a video, or a podcast. For support,go to ScienceSource.

3. Would you expect an employee of a chemicalplant to come to the same conclusions about thehealth problems on the Aamjiwnaang First NationReserve as Lockridge and her colleagues? Why?

4. Environmental Health Perspectives is a peer-reviewed journal. A peer-reviewed journal is one in which expert scientists must review and approve research before it is published. Do you think it was important for Lockridge andher colleagues to publish their research in a peer-reviewed journal? Why?

Skill Practice

5. Identify any sources of bias in this report.

Figure 4.19 Ada Lockridge

Skills References 4, 5, 6Decision-Making Analysis

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Key Concept Review1. Name two properties of matter.

2. What are the two categories of puresubstances in the matter classification treeshown in Figure 4.5 on page 143?

3. How is an element different from acompound?

4. Name four families of elements in theperiodic table.

5. What is the relationship between anelement’s atomic number and the number ofprotons in the nucleus of each of its atoms?

6. Name three types of subatomic particles, andthen state the charge on each.

7. What is an ion?

Connect Your Understanding8. Invent and describe a simple way to

remember that a horizontal row on theperiodic table is called a period and a verticalcolumn is called a family or group. Forexample, you could use a sentence, an image,or word association.

9. Design and draw a table to compare thenames and characteristics of the threesubatomic particles described in this section.

10. Draw a Bohr diagram of an atom that has fiveprotons, six neutrons, and five electrons.Using the periodic table on page 147, identifythe element. Label the nucleus, the subatomicparticles, and the valence shell.

11. The atomic number of lithium is 3, and theatomic number of neon is 10.

(a) Draw a Bohr diagram of a lithium atomand of a neon atom.

(b) How many valence electrons are in thelithium atom and in the neon atom?

12. Compare the structure of atoms to thestructure of something else in everyday life.For example, you could compare an atom toan onion. Use as many of the chemistry termsin this section as you can.

13. Suppose you place a kettle on the stove andboil some water. Is the steam that formsevidence of a chemical change or a physicalchange? Explain.

14. The photo shows what happens whencalcium metal is placed in liquid water.Suggest whether a chemical or a physicalchange occurs when this happens. Explain.

Reflection15. Describe three things about atoms that you

did not know before starting work on this section.

For more questions, go to ScienceSource.

4.1 CHECK and REFLECT


Question 14

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Powering Up with Lithium IonsMany devices rely on a portable power source, including calculators,cellphones, handheld music and video players, and laptops (Figure 4.20). Most portable power sources use ions to generateelectrical energy. Ions are electrically charged atoms or groups of atoms.They form when electrons are traded between atoms of differentelements. Ions are actually forming around us all the time. For example,when iron atoms and oxygen atoms interact in the presence of salt andwater, the iron corrodes and rust is formed. As iron corrodes, iron ionsand oxygen ions are formed. Iron ions have a positive charge, andoxygen ions have a negative charge. The formation of these ionsreleases energy, but the energy is lost when a car body turns to rust.

When corrosion happens inside the tiny battery inside a hearingaid, however, the energy is not lost. This type of battery uses thecorrosion of zinc by oxygen to produce enough electricity to power thespeaker and microphones in the hearing aid. As zinc ions form duringcorrosion, electrons are released. These electrons travel from the batteryand through the components of the hearing aid, providing electricalenergy. The electrons travel back to the other pole of the battery andtoward oxygen atoms in the air, completing the electrical circuit.


• An ion is any atom (or group ofatoms) that has lost or gainedone or more electrons.

• All ions have either a positive ora negative charge.

• Metals and non-metalscombine to form ioniccompounds.

• Molecules can form betweenatoms of the same non-metal.

• Molecular compounds formbetween at least two differentnon-metal atoms.

Ions, Molecules, and Compounds

Figure 4.20 Laptop computers first become truly portable in 1999, when ion batteries becamemore widely available.

4.2

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Ion batteries depend on atoms of reactive metals. The more reactivethe metal, the more electrical energy they can potentially produce.Lithium metal is far more reactive than either iron or zinc metal.Lithium ion batteries are therefore able to supply far more electricalenergy than ion batteries made from these other metals. However, thereactivity of lithium initially caused problems. Early lithium ionbatteries produced a lot of heat and sometimes hydrogen gas. Thissometimes caused these early batteries to catch fire or explode while inuse. These problems have been eliminated in lithium-based batteries.Fortunately, battery technology constantly changes. Lithium ionbatteries are now so safe that they are used in medical devices such aspacemakers (Figure 4.21).

B5 Quick Lab

Solubility of Chemical Compounds

In this activity, you will divide four compounds intogroups by determining if they are soluble in water atroom temperature.

PurposeTo observe the solubility of four compounds

Procedure

1. Place the test tubes in the test-tube rack. Usingthe graduated cylinder, measure and add 5 mL of room temperature water to each test tube.

2. Using the scoopula, place a few crystals ofsodium chloride into the water in a test tube.Observe whether any crystals dissolve (Figure 4.22). The fewer the number of crystals you place in the test tube, the easier it will be toobserve if any dissolve.

3. Record your observations.

4. Repeat steps 2 and 3 for each of the remainingthree substances.

5. Clean up your work area. Make sure to followyour teacher’s directions for safe disposal ofmaterials. Wash your hands thoroughly.

Questions

6. Which substance was most soluble? Which wasleast soluble? Explain how you decided.

7. Do you think that the property of solubility isenough to identify the compounds? If yes,explain. If no, suggest other properties that mightbe helpful in identifying these compounds.

Figure 4.22 Add a few crystals, and then observe whether theydissolve. You can gently swirl the test tube.

• 4 test tubes

• test-tube rack

• waterproof marker

• water

• 10-mL graduatedcylinder

• scoopula

• single chip of calciumcarbonate

• piece of candle wax

• sodium chloride

• sugar


Figure 4.21 The medical devicespictured here are called artificialpacemakers. Each one has a batterythat uses ions to produce electricity.People whose natural pacemaker intheir heart does not function properlymay use an artificial pacemaker.

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Text FeaturesIndicate Important Ideas

Textbook authors give you clues

about what is important by using

special text features. Words may

be in bold type. Charts summarize

important information. Diagrams

and pictures help you to see and

understand objects and concepts.

Make a note of four text features

and how they helped you to

understand new information and

ideas.

During Reading Compounds: Ionic and MolecularA compound is a pure substance made up of two or more elements, inwhich the elements are chemically combined. For example, water (H2O)is a compound that consists of the elements hydrogen and oxygen. In it,the hydrogen atoms are joined to the oxygen atoms by connectionscalled chemical bonds. There are two main types of compounds: ioniccompounds and molecular compounds.

Ionic Compounds Recall that an ion is an atom or group of atoms that has either a positivecharge or a negative charge. An ionic compound is a compound that isformed from one or more positively charged ions and one or morenegatively charged ions.

Ions form when atoms of different elements combine ina process involving the transfer of electrons from one atomto another. For example, this process occurs when atoms ofsodium metal combine with atoms of chlorine to formsodium chloride, which is commonly called table salt(Figure 4.23). During the formation of sodium chloride, oneelectron is transferred from a sodium atom to a chlorineatom. This is illustrated by Bohr diagrams in Figure 4.24.Each sodium metal atom loses one electron and becomes apositively charged ion, which is symbolized as Na+. Thesymbol “+” is written as a superscript to indicate that thesodium has a charge of 1+. Each chlorine atom gains oneelectron to become a negatively charged ion. A chlorine ionis symbolized as Cl–, where the “–” indicates a charge of 1–.

156

Cl-

1-

Na+ClNa

1+

Figure 4.24 Bohr diagrams can be used to show the transfer of an electron from a Na atom to a Cl atom. Thisprocess forms the ions Na+ and Cl�.


chlorine gas

sodium chloride

sodium metal

Figure 4.23 Sodium metal and chlorine gas react toform the ionic compound sodium chloride (NaCl).

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Notice in Figure 4.24 (on the previous page) that both ions haveeight electrons in their outermost shells. Ions often form in a way thatproduces filled outermost shells. Metal atoms tend to lose electrons,while non-metal atoms tend to gain them. Often, all that is needed forthis to happen is for atoms of the two elements to be brought together.

Ionic compounds have a number of properties in common.

• At room temperature, most are hard, brittle solids that can be crushed.

• Ionic compounds form crystals that have an alternatingarrangement of positively charged ions and negatively chargedions (Figure 4.25). As a result, when ionic crystals are broken,flat surfaces and well-defined edges are formed.

• In an ionic crystal, every ion is attracted to every other ion in thecrystal. As a result, ionic crystals have very high melting points.For example, sodium chloride melts at 800ºC.

• When an ionic compound dissolves in water, the crystal structurebreaks down and the ions become free to move. Solutions of ioniccompounds therefore conduct electricity.

Ion Symbols and NamesNot all atoms will form ions, and some atoms can form an ion in morethan one way. Information on the periodic table shows the ion charge ofions that will form for each element (see Figure 4.11 on page 147).Table 4.4 shows some examples of ions of some elements.

157

CI-Na+

Figure 4.25 The structure of crystalsof sodium chloride

Element Ion Charge Symbol Name

sodium 1+ Na+ sodium

calcium 2+ Ca2+ calcium

aluminum 3+ Al3+ aluminum

fluorine 1– F– fluoride

oxygen 2– O2– oxide

nickel 2+ 3+

Ni2+

Ni3+nickel(II)nickel(III)

lead 2+ 4+

Pb2+

Pb4+lead(II)lead(IV)

gold 3+ 1+

Au3+

Au+gold(III)gold(I)

Table 4.4 Some Examples of Ions


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Learning Checkpoint

Refer to the periodic table in Figure 4.11 on page 147 to answer questions 1 and 2.

1. Write the symbol for the following ions:

(a) magnesium (c) iron(II) (e) uranium(VI)

(b) chloride (d) chromium(III)

2. Write the name of the following ions:

(a) Zn2+ (c) Co2+ (e) Pb4+

(b) N3� (d) Co3+

Ion SymbolsTo write the symbol for an ion, write the symbol of the element andshow the ion charge as a superscript. For example, the symbol of acalcium ion is Ca2+. When an ion has a charge of 1+ or 1–, the symbolhas no number in the superscript, such as for Na+ and F–.

Ion NamesWhen an element can form only one type of ion, such as calcium, theion has the same name as the element. However, the atoms of manymetals can form more than one type of ion. For example, an atom ofcopper can form one of two different ions, one with a charge of 1+ orone with a charge of 2+.

A multivalent element is an element that can form an ion in morethan one way. Many metal elements are multivalent. The name of anion of a multivalent element always contains a Roman numeral thatindicates the ion charge. Table 4.5 shows the numbers one to sevenwritten as Roman numerals.

For example, Cu+ is named copper(I), which is read as “copperone.” Similarly, Cu2+ is named copper(II), which is read “copper two.”Copper(II) ions are found in the ionic compound copper(II) chloride(Figure 4.26). Only multivalent metals have Roman numerals in their names.

Number RomanNumeral

1 I

2 II

3 III

4 IV

5 V

6 VI

7 VII

Table 4.5 Some Roman Numerals

Figure 4.26 Crystals of the ioniccompound copper(II) chloride

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159

WORDS MATTER

“Subscript” derives from the Latinword subscribere, which meanswritten below.

Naming Ionic CompoundsUse the following rules to name an ionic compound from its formula.

1. Name the metal ion first. The name of the metal ion is the sameas the element name. For example, in KBr, the name of the K+ion is potassium. If the element can form an ion in more thanone way, include a Roman numeral to indicate the charge.

2. Name the non-metal ion second. When a non-metal becomes anegative ion, the ending of its name changes to “ide.” Forexample, a bromine atom (Br) gains an electron to become abromide ion (Br–).

3. Name the ionic compound by combining the ion names. Thename of KBr is, therefore, potassium bromide.

Name of metal Name of non-metal + idepotassium bromide

Table 4.6 shows some examples of how theserules are applied. The formulas of ioniccompounds often contain numbers, calledsubscripts, such as the “3” in Na3P. (You will findout what subscripts mean later in this section.) Ifthe metal forms only one type of ion, the subscriptcan be ignored when determining the name.

Example Problem 4.1

Write the name of the ionic compound ZnF2.

1. Name the metal ion: Zn forms only one type of ion (Zn2+), sothe name is zinc.

2. Name the non-metal ion: The atom is fluorine, so the ion isfluoride.

3. Combine the names: zinc fluoride.

Practice Problems

Write the names of the followingionic compounds.

1. LiBr

2. CaI2

3. Al2O3

4. Mg3N2

Compounds Containing Multivalent ElementsRecall that the name of an ion of a multivalent element always containsa Roman numeral to indicate its charge. For example, the namenickel(II) sulphide indicates that the Ni2+ ion forms the compound,while the name nickel(III) bromide indicates that the Ni3+ ion ispresent.

Formula PositiveIon

NegativeIon

Name

CaS Ca2+ S2– calcium sulphide

MgCl2 Mg2+ Cl– magnesium chloride

Na3P Na+ P3– sodium phosphide

Table 4.6 Naming Ionic Compounds


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You can determine which Roman numeral to use in the name of amultivalent ion from the subscript(s) in the compound’s formula. Forexample, the subscript 3 in the formula CrCl3 is a guide to the charge ofthe chromium ion in this compound. There is a special relationshipbetween the numbers of positive and negative charges in any ioniccompound. All ion charges in an ionic compound must add up to zero.Another way of saying this is that although an ionic compound is madeup of charged particles, the compound itself has no net charge.

From this, we get the following rule:

• The positive and negative charges in an ionic compound must be equal.

According to this rule, a Cr3+ ion must always combine with threeCl– ions, which gives the 1:3 ratio in the formula. The name of CrCl3 iswritten as chromium(III) chloride. Chromium(III) chloride is abeautiful colour and is used to colour glass (Figure 4.27).


Example Problem 4.2

Write the name of the ionic compound TiI4.

1. Identify the ions that form the compound: Ti4+ and I–.

2. Use the charge on the non-metal ion and the rule that the totalpositive and negative charges in the formula must be equal.

• One titanium ion is present in the formula, so it must have a charge of 4+.

3. Name the metal ion.

• The ion has a 4+ charge, so the name is titanium(IV).

4. Name the non-metal ion.

• The name of the atom is iodine, so the ion is iodide.

5. Combine the names: titanium(IV) iodide.

Practice Problems

Write the names of thefollowing ionic compounds.

1. FeCl2

2. FeCl3

3. Cu3N2

4. Ni2O3

Polyatomic IonsA polyatomic ion is a group of atoms, usually of different elements,that act as a single ion. For example, one atom of sulphur and fouratoms of oxygen form the polyatomic ion called sulphate, or SO4

2–. Thision is present in many compounds. For example, the sulphate ion iscombined with the lead(II) ion in PbSO4, which is used in car batteries,with the copper(II) ion in CuSO4, which can kill fungus, and with themagnesium ion in MgSO4, which is called Epsom salts and is added tobathwater.

Figure 4.27 Chromium(III) chloride isused in the manufacture of colouredglass.

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Similar polyatomic ions are named using the suffixes “-ate” or “-ite.” For example, nitrate (NO3

�) is similar to nitrite (NO2�).

Compounds that contain nitrates and nitrites are present in manypreserved foods, such as hot dogs (Figure 4.28).

Most common polyatomic ions have a negative charge. However,one common polyatomic ion has a positive charge. The ammonium ion,NH4

+, is composed of one nitrogen atom and four hydrogen atoms andit has a charge of 1+. Examples of common polyatomic ions are given inTable 4.7.

In some cases, the formula of an ionic compound uses brackets tohelp identify the polyatomic ion. Table 4.8 gives some examples andhints for writing the names of ionic compounds with polyatomic ions.

Name Formula

ammonium NH4+

carbonate CO32�

hydrogen carbonate(bicarbonate)

HCO3�

hydroxide OH�

nitrate NO3�

nitrite NO2�

permanganate MnO4�

phosphate PO43�

phosphite PO33�

sulphate SO42�

sulphite SO32�

Table 4.7 Common Polyatomic Ions

Formula Positive Ion Negative Ion Name Hint for Writing Name

Al(OH)3 Al3+ OH– aluminum hydroxide • The polyatomic ion is often found inbrackets.

NiSO4 Ni2+ SO42– nickel(II) sulphate • Brackets are not always used.

• Everything after the metal is part of thepolyatomic ion.

Table 4.8 Naming Ionic Compounds with Polyatomic Ions

Example Problem 4.3

Write the name of the ionic compound LiHCO3.

1. Name the metal ion (or ammonium ion).

• Li forms only one type of ion (Li+), so the name is lithium.

2. Identify the polyatomic ion by examining the formula andcross-checking with the table of common polyatomic ions.

• The name for HCO3� is hydrogen carbonate.

3. Combine the names: lithium hydrogen carbonate.

Practice Problems

Using Table 4.8, write the namesof the following ioniccompounds.

1. Al2(SO4)3

2. Ca3(PO4)2

3. Fe(OH)2

4. (NH4)2S

Figure 4.28 Preserved meats, suchas hot dogs, stay red due to theaddition of potassium nitrate andsodium nitrite.

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Writing Formulas for Ionic CompoundsIt is possible to write the chemical formula for an ionic compound fromits name. In many cases, the chemical formula must include one ormore subscripts. In the formula of an ionic compound, a subscript tellsyou the ratio of each ion that is in the compound. When there is nosubscript, there is only one of that ion.

For example, in the formula for aluminum trioxide, Al2O3, there is asubscript 2 next to the symbol Al and subscript 3 by the symbol O.Aluminum oxide therefore contains two aluminum ions for every threeoxygen ions. The semi-precious stone called sapphire is composedmainly of Al2O3. The blue colour is produced by trace impurities, suchas the element chromium (Figure 4.29).

How do you determine if the chemical formula includes a subscript?Recall the rule that the positive and negative charges in an ioniccompound must be equal. If the charges are not equal, add ions until the charges are balanced. Indicate in the formula the total number of each ion with a subscript. If there is only one of an ion, do not add a subscript.

Table 4.9 presents steps for writing the formulas for ioniccompounds and shows how they are used in three examples.


StepsExamples

calcium bromide magnesium nitride copper(II) oxide

1. Examine the name of the compound.Identify the ions and their charges.

calcium: Ca2+

bromide: Br–

magnesium: Mg2+

nitride: N3–

copper(II): Cu2+

oxide: O2–

2. Determine the number of each ionneeded to balance the charges.

Ca2+

Br– Br–

Mg2+ Mg2+ Mg2+

N3– N3–

Cu2+

O2–

3. Note the ratio of positive to negativeions, and write the formula.

1 to 2 3 to 2 1 to 1

4. Write the chemical formula, usingsubscripts if needed.

CaBr2 Mg3N2 CuO

Table 4.9 Steps for Writing Formulas for Binary Ionic Compounds

Figure 4.29 Sapphires arecomposed mostly ofaluminum oxide.

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163

Example Problem 4.4

Write the formula for aluminum oxide.

1. Identify the ions and their charges: Al3+ and O2–.

2. Determine the number of each ion needed to balance the charges.

Al3+ Al3+ O2– O2– O2–

3. Note the ratio of positively charged ions to negatively chargedions, and write the formula: Al2O3.

Practice Problems

Write the formulas for thefollowing ionic compounds.

1. potassium iodide

2. magnesium phosphide

3. silver sulphide

4. iron(III) bromide


Formulas for Compounds with Polyatomic IonsThe rules for writing formulas for compounds containingpolyatomic ions are similar to the rules for other ionic compounds.The rule is still that the positive and negative charges in an ioniccompound must be equal. The main difference is that brackets maybe used to show the ratio of ions. For example, in Cr(HCO3)3, thereis one Cr3+ ion for every three HCO3

– ions.Table 4.10 shows how to identify ions for four examples of this

type of ionic compound and how to write their formulas. Considercalcium carbonate, a common ingredient in antacids (Figure 4.30).Notice that for calcium carbonate, the 2+ charge on the Ca2+

balances the 2– charge on the polyatomic ion CO32–. Since there is

one Ca2+ for every CO32–, the formula for calcium carbonate is

CaCO3. Brackets are not needed.

Suggested Activity •B6 Quick Lab on page 169

Figure 4.30 Calcium carbonate iscommonly used in antacids.

Name calciumcarbonate

ammoniumsulphide

iron(III) hydroxide ammonium phosphate

Ions Ca2+ CO32– NH4

+ S2– Fe3+ OH– NH4+ PO4

3–

Ratio of Ions Ca2+

CO32–

NH4+ NH4

+

S2–

Fe3+

OH– OH– OH–

NH4+ NH4

+ NH4+

PO43–

Formula CaCO3 (NH4)2S Fe(OH)3 (NH4)3PO4

Table 4.10 Examples of Polyatomic Ions in Formulas

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Example Problem 4.5

Write the formula for nickel(II) phosphate.

1. Identify the ions and their charges: Ni2+ and PO43–.

2. Determine the number of each ion needed to balance thecharges.

Ni2+ Ni2+ Ni2+ PO43– PO4

3–

3. Note the ratio of positively charged ions to negatively charged ions.

three Ni2+ for every one PO43–

4. Use the ratio to determine what subscripts to use. If asubscript is needed for a polyatomic ion, include brackets andplace the subscript outside the brackets.

A subscript of 3 is needed after the Ni2+.A subscript of 2 outside a bracket is needed for PO4

3–.

5. Write the formula: Ni3(PO4)2.

Practice Problems

Write the formulas for thefollowing ionic compounds.

1. magnesium hydroxide

2. sodium sulphate

3. lead(IV) nitrate

4. ammonium carbonate

WORDS MATTER

The word “diatomic” is formed fromthe prefix “di-” (two) and the word“atomic” (made of atoms).

Molecular ElementsA molecule is a combination of two or more atoms held together bycovalent bonds. A covalent bond is a connection, usually between theatoms of non-metals, in which the two atoms share a pair of electrons.The electron pair belongs to both atoms, and the attraction of the atomsfor the same electron pair holds them together.

Several important non-metals exist as molecules. In a molecularelement, two or more atoms, all of the same element, are joined bycovalent bonds. A diatomic molecule is a molecule that is made fromtwo atoms. For example, the element chlorine is a molecular elementthat exists as a diatomic molecule (Figure 4.31).

The formulas for diatomic molecules contain a subscript. In theformula of a molecule, a subscript tells you the number of each atom inthe molecule. A chlorine molecule is symbolized as Cl2. The subscript 2indicates that two chlorine atoms are present. Other non-metalelements exist as molecules too. The elements oxygen and nitrogen,which form 99 percent of the air, are also diatomic.

Figure 4.31 Elemental chlorine is a diatomic molecule (Cl2). Chlorine dissolves in water and isused to disinfect water in drinking supplies and swimming pools.

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165

Table 4.11 Elements ThatCommonly Form DiatomicMolecules

Element Formula

bromine Br2

chlorine Cl2

fluorine F2

hydrogen H2

iodine I2

nitrogen N2

oxygen O2

Figure 4.32 uses Bohr diagrams to illustrate the sharing of electronsin a covalent bond between two chlorine atoms. Table 4.11 shows theelements that commonly exist as diatomic molecules.

Another form of oxygen is called ozone and has the formula O3.Ozone is essential in the upper atmosphere to filter out deadly UV rays.At ground level, O3 is a pollutant. The elements hydrogen, sulphur,phosphorus, nitrogen, and all the halogens, such as fluorine, exist asmolecules.

One molecule of CI2: two chlorine atoms share one electron each to form one pair of shared electrons.

Figure 4.33 This model of a moleculeof glucose is composed of 6 carbonatoms (black), 12 hydrogen atoms(white) and 6 oxygen atoms (red).

Figure 4.32 A molecule of chlorinegas forms when two chlorine atomsjoin by sharing one pair of electrons.

Molecular Compounds When atoms of two or more different non-metals combine, a puresubstance known as a molecular compound is formed. Glucose is anexample of a molecular compound. Molecules of glucose are carried byyour blood to the cells of your body, where they are broken down tosupply energy. The chemical formula for glucose is C6H12O6. Thesubscripts in this formula show that a single glucose molecule contains6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. Altogether,there are 24 atoms connected together in one glucose molecule, asshown in Figure 4.33.

As with molecular elements, the atoms in molecular compounds arejoined together by covalent bonds. In each bond, the atoms share asingle pair of electrons. For example, water is a molecular compound(Figure 4.34). There are two covalent bonds in water. Each hydrogenatom shares one pair of electrons with an oxygen atom.

Figure 4.34 (a) Bohr diagram of a water molecule, showing how an oxygen atom (centre) sharesa pair of electrons with each of two hydrogen atoms (below). (b) Diagram of a water molecule,showing an oxygen atom (red) connected by covalent bonds to hydrogen atoms (white)

(b)


(a)

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Formula Name Application/Use

PCl5 phosphorus pentachloride production of lithium ion batteries

C3H8 propane camp fuel

SO2 sulphur dioxide production of sulphuric acid for carbatteries

C2F4 tetrafluoro ethylene production of Teflon plastics

C9H8O4 acetylsalicylic acid pain control medication

C6H8O6 ascorbic acid vitamin C

Table 4.12 Some Molecular Compounds and Their Formulas

Figure 4.35 Melted sugar is used tomake a number of types of candy.

Table 4.12 shows some examples of molecular compounds that maybe familiar.

Properties of Molecular CompoundsMolecular compounds have a number of properties in common.

• They are often soft.

• If they dissolve in water, they form solutions that do not conductelectricity.

• They tend to have relatively low melting points. For example,white table sugar can be melted on a stove. The chemical namefor table sugar is sucrose, and its formula is C12H22O11. Meltedsugar is used to make candies such as caramel, butterscotch, andpeanut brittle (Figure 4.35).

The same two non-metallic elements can alsocombine in different ways and form differentmolecular compounds with different properties.For example, hydrogen and oxygen can combineto make water (H2O) or hydrogen peroxide(H2O2). A molecule of water is made up of twoatoms of hydrogen combined with one atom ofoxygen. A molecule of hydrogen peroxide is madeup of two atoms of hydrogen combined with twoatoms of oxygen.

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Naming Binary Molecular CompoundsRecall that a binary compound contains exactly two elements. Thenames of binary molecular compounds that do not contain hydrogenatoms use Greek prefixes to indicate how many atoms of each elementare present in a compound. The prefixes are listed in Table 4.13. Forexample, P2O5 is a molecular compound used in the manufacture ofmedicines. Its name is diphosphorus pentoxide. The “di” means “2,”and the “pent” comes from “penta” and means “5”.


Number of Atoms Prefix

1 mono-

2 di-

3 tri-

4 tetra-

5 penta-

6 hexa-

7 hepta-

8 octa-

9 nona-

10 deca-

Table 4.13 Prefixes Used in NamingMolecules

StepsExamples

N2O PBr3

1. Name the first element. nitrogen phosphorus

2. Name the second element,using the suffix “-ide”.

oxide bromide

3. Add prefixes to indicate thenumber of each atom.

dinitrogen monoxide phosphorus tribromide

Table 4.14 Examples for Naming Binary Molecular Compounds


The rules in Table 4.14 will help you to name binary molecularcompounds. Note that the prefix “mono-” is not used when the firstelement is only one atom. When the prefix “mono-” is required before“oxide,” the last “o” in the prefix is dropped. For example, it is“monoxide,” not “monooxide.”

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Naming Binary Molecular CompoundsUsing the name, you can write the formula of a binary molecularcompound. The prefix indicates the number of atoms of each typeof element (Table 4.13 on page 167).


Example Problem 4.7

Write the formula for disulphur decafluoride.

1. Identify the first element, and give its symbol: sulphur, S.

2. Identify the second element, and give its symbol: fluorine, F.

3. Add subscripts to indicate the numbers of atoms. • The prefix “di” indicates that a subscript of 2 is needed

after S.• The prefix “deca” indicates that a subscript of 10 is needed

after F.4. Write the formula: S2F10.

Practice Problems

Write the chemical formulas forthe following binary molecularcompounds:

1. sulphur hexabromide

2. carbon tetrachloride

3. dinitrogen tetroxide

4. tetraphosphorus decaoxide

Example Problem 4.6

Write the name for N2S3.

1. Name the first element: nitrogen.

2. Name the second element, which ends with “ide”: sulphide.

3. Add prefixes indicating the numbers of atoms: dinitrogentrisulphide.

Practice Problems

Write the names of the followingbinary molecular compounds:

1. SO3

2. P4S10

3. NF3

4. N2O

water, H2O hydrogen peroxide, H2O2

H H

O

H

O

H

O

Figure 4.36 These ball-and-stick models ofwater and hydrogen peroxide show that bothmolecules contain atoms of hydrogen andoxygen, but in different proportions.

Hydrogen is unique in many ways, and this is reflected innaming systems. Many compounds containing hydrogen havesimply been given names. For example, the name “water” waschosen as the chemical name for H2O simply because it wasconvenient to do so. Another binary compound containing onlyhydrogen and oxygen, H2O2, is called hydrogen peroxide. Thiscompound is a disinfectant and bleaching agent. The structures ofthese compounds are shown in Figure 4.36. Two other commonbinary compounds of hydrogen are CH4, called methane, and NH3,called ammonia. These are summarized in Table 4.15.

Name Formula

water H2O

hydrogen peroxide H2O2

ammonia NH3

methane CH4

Table 4.15 Common BinaryMolecular CompoundsContaining Hydrogen

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B6 Quick Lab

Paper models of individual ions can be used to findthe correct ratio of the ions in a compound.

PurposeTo use paper models of polyatomic ions and atomsand the periodic table to work out formulas for ioniccompounds

Procedure

1. Cut out the paper ions with various charges fromthe templates.

2. Observe that some paper ions will have one, two,three, or four extra pieces pointing out, whileothers will have one, two, three, or four piecesmissing. These represent the charge on each ion.For example, three pieces missing means “3+”.

3. Use the periodic table and the table of commonpolyatomic ions on page 161 to work out thecharges for each of the ions in the compoundslisted below. Pick a template with the right chargefor each ion and label it (Figure 4.37).

(a) calcium chloride

(b) aluminum fluoride

(c) magnesium bromide

(d) lithium nitride

(e) ammonium hydroxide

(f) barium sulphate

4. Using the paper ions, create models for each ofthe ionic compounds listed in step 3. Somecompounds will need more than one of each kindof ion.

5. Choose a binary ionic compound that is not on thelist. Write its name and its chemical formula, andbuild a model of the compound using the paperions.

Questions

6. Although each ion that makes up an ioniccompound has a charge, the ionic compounditself is neutral. Why?

7. Did making models of compounds withpolyatomic ions differ from making models ofcompounds without polyatomic ions? How werethey the same or different?

Paper Models of Ionic Compounds

Figure 4.37 Paper models of atoms and polyatomic ions canhelp you to see how to balance the charges to form an ioniccompound with a neutral charge.

• templates for ions withvarious charges

• scissors

• envelope

• periodic table

• table of commonpolyatomic ions


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B7 Quick Lab

PurposeTo construct ball-and-stick models of some simplemolecules using a molecular modelling kit

Procedure

1. Following your teacher’s instructions, work in asmall group to use the molecular model kit. Whenbuilding molecular models, keep the followingguidelines in mind:

• Each molecule is complete when all the ballsare connected so that all holes are filled andevery connector ends in a hole (Figure 4.38).

• In some cases, more than one connection canexist between the same two atoms.

2. For each of the following, build the model and thendraw and label a sketch of it. Do not take yourmodels apart until you have completed step 3.

(a) H2 (hydrogen gas, used in some balloons)

(b) O2 (oxygen, a gas we breathe in)

(c) H2O (water, makes up about 60% of yourbody)

(d) H2O2 (hydrogen peroxide, a bleaching agent)

(e) CO2 (carbon dioxide, a gas we breathe out)

3. Compare the models built in step 2.

(a) Name and sketch one molecule containingthree atoms that has a bent shape and one thatis not bent. Include labels on your sketches.

(b) Explain how water can be a pure substanceeven though it contains two different elements.

4. Build models of carbon tetrachloride (CCl4) and ofmethane (CH4) and compare their shapes. Drawand label one diagram only of the shape of bothmolecules. Try to draw the shape in 3D.

5. The following molecules can be constructed inonly one way. Build, sketch and label each. It isnot necessary to try to show them in 3D. Do nottake your models apart until you have completed step 6.

(a) C2H2 (acetylene, used in welding)

(b) C2H4 (ethylene, used in plastics manufacture)

(c) C2H6 (ethane, used in plastics manufacture)

6. Compare the models built in step 5. One modelhas parts that can rotate. The other two do not.Using the terms single bond, double bond, andtriple bond, explain why only some moleculeshave parts capable of rotating.

7. The following molecules can be constructed inmore than one way. Each different way ofconstructing a molecule produces a different puresubstance. Build and sketch all possible forms ofeach of the following molecules.

(a) C3H7Cl (two ways)

(b) C2H6O (two ways)

(c) C2H2Cl2 (three ways)

Questions

8. Examine the drawings you made for hydrogengas, oxygen gas, and chlorine gas. What is thedifference between bonding in hydrogen andchlorine, compared to oxygen?

9. Consider all the models you built during this lab,and suggest a reason why there are manydifferent kinds of compounds containing carbon.

Modelling Molecules

Figure 4.38 A ball-and-stick model of a molecule

• ball-and-stick chemical modelling kit


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Key Concept Review1. What is an ion?

2. What symbols do we use to indicate thatatoms have become ions?

3. What is the purpose of a subscript whenwriting the formula for the following?

(a) a binary ionic compound

(b) a molecular compound

4. What combinations of two elements combineto form ionic compounds?

5. What is a molecular compound?

Connect Your Understanding6. Name the following ions.

(a) Al3+ (d) S2–

(b) Ca+ (e) SO42–

(c) Br– (f) PO43–

7. Write the chemical formula for each of thefollowing ionic compounds.

(a) beryllium oxide

(b) rubidium bromide

(c) barium hydroxide

(d) ammonium iodide

(e) magnesium phosphate

(f) iron(III) oxide

(g) copper(I) sulphate

(h) chromium(III) phosphate

8. Write the chemical name of each thefollowing ionic compounds.

(a) ZnCl2(b) CaS

(c) K2SO4

(d) NH4NO3

9. How would you recognize a molecularcompound from its formula?

10. A polyatomic ion, such as NH4+ or CO3

2�,has several atoms joined together. Why is apolyatomic ion not called a molecule?

11. The Bohr diagram below illustrates theelectrons involved in the formation of H2.Explain the position of the electrons in theillustration.

12. Write the chemical name for each of thefollowing molecular compounds.

(a) SO2 (d) OF2

(b) SO3 (e) SI6

(c) PI3 (f) P2S4

13. Write the chemical formula for each of thefollowing molecular compounds.

(a) sulphur hexabromide

(b) nitrogen tribromide

(c) sulphur hexachloride

(d) diphosphorus pentoxide

(e) carbon monoxide

Reflection14. List questions for further study that you have

about ions, ionic compounds, and molecules.




(e) Sr3(PO4)2

(f) AuCl3(g) Ni2S3

(h) PbF4

Question 11

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Chemistry and Automobile Safety Many of Ontario’s major highways are highly congested (Figure 4.39).Heavy traffic increases the chance that a vehicle will be involved in acollision. Over the years, changes in vehicle designs have made it lesslikely that you will be badly injured or killed in a collision. Thesechanges include adding seat belts with shoulder restraints, makingspecific zones in a vehicle body that will easily crumple and absorb theenergy of a collision, and even placing the bumpers of all vehicles at thesame height above the road.

Another important safety feature is the airbag. Airbags are builtinto the steering wheels and dashboards and, in some cases, the sides ofa vehicle. If the vehicle slows down very suddenly, like it might in acollision, the airbags inflate, which prevents the driver and passengerfrom hitting the inside of the vehicle cabin. Collisions can happen veryquickly, so airbags must inflate very fast to be effective. Modern airbagstake less than 0.05 seconds to inflate. This fast response time relies on achemical reaction within the airbag.


• In a chemical reaction, theatoms in one or more puresubstances are rearranged toproduce at least one new puresubstance.

• The law of conservation ofmass describes what happensto the atoms involved in achemical reaction.

• Word equations and chemicalequations are two ways to writea chemical reaction.

• In a balanced chemicalequation, the number of eachkind of atom on the reactantsside of the equation is thesame as the number of thoseatoms on the products side ofthe equation.

Chemical Reactions

Figure 4.39 Many highways and roads in Ontario have heavy traffic every day. This increasesthe risk of being involved in a traffic accident.

4.3

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During a collision, a sensor in the airbag detects that thevehicle has slowed down suddenly. In response, a small pelletof sodium azide (NaN3(s)) is heated, producing harmlessnitrogen gas (N2(g)), which inflates the airbag (Figure 4.40).This reaction is written using chemical symbols as shownbelow. In the equation, “s” stands for solid and “g” stands for gas.

2NaN3(s) → 3N2(g) + 2Na(s)

The other product of this reaction is sodium metal (Na).Sodium metal will react with water to form a chemical thatwill damage skin and tissues, so it would be harmful if it gotinto your eyes, nose, or mouth. Airbags contain othersubstances that quickly react with the sodium metal. Thesereactions convert the sodium to less harmful chemicals,which prevents a person being injured by sodium metalwhen an airbag inflates.

B8 Quick Lab

Observing Chemical Changes (Teacher Demonstration)

PurposeTo observe your teacher combine chemicals toproduce chemical change

Procedure

1. Working in a fume hood, your teacher will use thesteel wool to make a short circuit between theterminals of the 9.0-V battery. Record yourobservations.

2. Working in a fume hood, your teacher will light asmall piece of magnesium ribbon in the beaker.Observe and record what happens.

Questions

3. What gas or gases in the air may have beeninvolved in the chemical changes you observed?

4. New pure substances are formed during achemical change. What pure substance(s) do youthink were formed in step 1 and step 2?

Figure 4.40 Airbags have helped to reduce thenumber of deaths due to head-on collisions.

CAUTION• Use a fume hood.• Keep back to the distance instructed by your teacher.

Burning steel wool can create sparks that could causeburns.

• Observe the reaction only through UV-absorbing glass.• If you have a history of seizures, avoid looking directly

at the light.• Do not touch the reactants and products.

• steel wool

• 9.0-V battery

• magnesium ribbon

• large beaker

• tongs

• lab burner

• matches or flamestriker


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Chemical ReactionsA chemical change is the transformation of one or more substancesinto different substances, with different properties. A chemicalreaction is a process by which chemical change happens. All chemicalreactions are also accompanied by changes in energy. Some chemicalreactions absorb energy, such as in the chemical reactions that cookfood. Other chemical reactions release energy in the form of heat, light,and/or sound, such as the burning of wood in a campfire (Figure 4.41).

Chemical reactions happen at different rates. Some chemicalreactions are fast, such as when rocket fuel burns. Other chemicalreactions happen slowly, such as the formation of rust on a corrodingbicycle chain. The chemical reactions in your own body, which arekeeping you alive and allowing you to read the words on this page, areamong the fastest chemical reactions known.

Chemical reactions are used in many ways in daily life. For example,chemical reactions produce the glow in glow sticks (Figure 4.42(a)),generate instant cold without ice in a cold pack (Figure 4.42(b)), and areused to manufacture pigments in artists’ paints, such as the bright yellowpigment in Figure 4.42(c).

Scientists are constantly working with chemical reactions to producenew substances with useful properties. For example, the chemicalreaction shown in Figure 4.42(c) is no longer used commercially becauseit involves the element lead. Today, lead is avoided as much as possible,because it is toxic to living organisms. Other kinds of chemical reactionshave been developed to produce yellow pigments that do not contain lead.

Reactants and ProductsAll chemical reactions involve the conversion of starting materials,called reactants, into new substances, called products. The productshave different properties than the reactants. These new reactions mayproduce substances with different colours or states. Recall that the term


Figure 4.42 (a) Chemical reactionscause light sticks to glow, whichmakes them useful in an emergency. (b) The chemical reaction in coldpacks absorbs heat, causing thetemperature to fall. (c) The chemicalreaction between these two solutionsproduces a yellow solid.

Figure 4.41 When wood burns, itreleases energy as light, sound, and heat.

(a)

(b)

(c)

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“state” refers to solid, liquid, and gas, as well as aqueous, which meansdissolved in water.

Consider the chemical reaction that occurs when a piece of solidmagnesium metal is placed into a solution of hydrochloric acid. Bubblesof hydrogen gas are formed during the reaction (Figure 4.43). A secondproduct, aqueous magnesium chloride, also forms.

Chemical EquationsA chemical reaction is often described by writing a chemical equation.A chemical equation uses either words or symbols and formulas todescribe the changes that occur during a chemical reaction. Forexample, the chemical reaction between solid magnesium metal andhydrochloric acid is:

Notice that the hydrogen is expressed in the formula equation asH2. Recall from Section 4.2 that pure hydrogen exists as a molecule. Youwill need to know which elements exist as molecules when writingformula equations. The chemical formulas in a formula equation oftenwill include the following:

• the state of matter of each substance. The state of each substanceis indicated by placing the appropriate symbol in brackets afterthe formula. These symbols are (s) for solid, (l) for liquid, (g) forgas, and (aq) for aqueous.

• one or more coefficients. A coefficient is an integer that is placed in front of the symbol of an element or a chemicalformula. The coefficients show the ratios of the differentsubstances that are present in the chemical reaction. In theformula equation above, a coefficient of 2 is in front of the formula HCl. This means that Mg and HCl combine in a ratio of 1:2.


Figure 4.43 Some chemical reactionsinvolve a change of state, such as theformation of bubbles in a liquid.

word equation: magnesium + hydrochloric acid → magnesium chloride + hydrogenformula equation: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

Learning Checkpoint

To answer questions 1 to 5, refer to the word equation and formula equation for

the chemical reaction above between magnesium metal and hydrochloric acid.

1. List the names of the reactants.

2. List the formulas of the products.

3. What is the state of the hydrochloric acid (HCl) and of the hydrogen (H2)?

4. What is the meaning of the arrow ( →) in the chemical equation?

5. Which symbol in the chemical equation means “reacts with”

or “is produced with”?

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Set a Purpose forReading

Having a purpose for reading helps

you to determine what is

important. You may be able to turn

a subheading into a question to

create your purpose for reading.

You may have to read a sentence

in the paragraph and then set a

purpose. For example, in reading

about the work of Antoine Lavoisier

and Marie-Anne Paulze, you might

want to know how that information

is related to chemistry. Choose a

paragraph or topic, and set a

purpose for reading.

During Reading

Conservation of MassThe most important advancement in understanding what happensduring chemical reactions was made about two centuries ago by thebrilliant French chemist Antoine Lavoisier (1743–1794), with theassistance of his wife and research colleague Marie-Anne Paulze (1758–1836). The couple made meticulous measurements of the massesof reactants and products in many kinds of chemical reactions.Sometimes, this was extremely difficult to do, especially when gaseswere involved.

What they discovered was that the total mass of reactants and thetotal mass of products in a given reaction are always the same. Anotherway of saying this is that the mass is conserved: the mass does notchange during a chemical reaction. No known exceptions to this haveever been observed. For this reason, this experimental result has cometo be known as a law.

The law of conservation of mass states that, in a chemicalreaction, the mass of the products always equals the mass of the reactants.

The law of conservation of mass is very important in understandingwhat happens to the atoms in chemical reactions. It implies that noatoms are destroyed and no new atoms are produced during a chemicalreaction. Instead, the atoms in the reactants of a chemical reaction aresimply rearranged to form the products. Chemical bonds between atomsare broken and new ones are formed, and the atoms simply reconnectin new ways.

Counting Atoms in Reactants and ProductsThe rearrangement of atoms that occurs during a chemical reaction can be illustrated using models or diagrams. Consider the vehicle inFigure 4.44. It runs on electricity produced in a fuel cell. The electricitycomes from a reaction between hydrogen gas and oxygen gas to formliquid water. The chemical equations for this reaction are:

word equation: hydrogen + oxygen → waterformula equation: 2H2(g) + O2(g) → 2H2O(l)

In the formula equation for this reaction, there are equal numbersof hydrogen atoms (four) and equal numbers of oxygen atoms (two) onboth the reactants side and the products side. When the number of eachkind of atom is the same in reactants and products, an equation is saidto be balanced.

176


Figure 4.44 Hydrogen and oxygengas combine chemically in a fuel cell. The reaction in the fuel cell produceselectrical energy to operate thevehicle.


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The balanced formula equation for the reaction between hydrogengas and oxygen gas is illustrated in Figure 4.45. You can check that it isbalanced by counting atoms. Table 4.16 shows the count of atoms onthe reactants side of the formula equation, and Table 4.17 shows thecount of atoms on the products side.



+

H2 H2 H2O H2OO2

+ +Figure 4.45 There are equalnumbers of hydrogen atomsand oxygen atoms on bothsides of this equation.

Symbols Description Elements Number of Atoms

2H2(g) 2 molecules of H2 H 2 molecules of H2= (2 molecules) � (2 H atoms per molecule) = 4 H atoms

O2(g) 1 molecule of O2 O 1 molecule of O2= (1 molecule) � (2 O atoms per molecule) = 2 O atoms

Table 4.16 Number of Atoms in the Reactants of the Formula Equation 2H2(g) + O2(g) → 2H2O(l)

Symbols Description Elements Number of Atoms

2H2O(l) 2 molecules of H2O H 2 molecules of H2O = (2 molecules) � (2 H atoms per molecule) = 4 H atoms

O 2 molecules of H2O = (2 molecules) � (1 O atom per molecule) = 2 O atoms

Table 4.17 Number of Atoms in the Products of the Formula Equation 2H2(g) + O2(g) → 2H2O(l)

Counting atoms shows that the numbers of hydrogen atoms (four)and oxygen atoms (two) are equal in the formula equation, just as theyare in Figure 4.45.

Learning Checkpoint

1. State the law of conservation of mass.

2. How does the law of conservation of mass tell you that reacting zinc with

hydrochloric acid can never produce aluminum oxide?

3. Suppose a solid substance with a mass of 10.0 g is heated in a chemical

reaction that produces a different solid substance and a gas, which escapes.

Suppose the new solid substance has a mass of 6.5 g. What mass of gas was

produced?

4. What is a balanced chemical equation?

5. Count the number of each kind of atom on both sides of this equation:

4K + O2 → 2K2O

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Writing Balanced Chemical EquationsA chemical equation that is complete except for coefficients is called anunbalanced equation or a skeleton equation. Example Problem 4.8shows a “guess-and-check” method for writing and balancing achemical equation. Example Problem 4.9 on page 179 shows a moredetailed method for balancing an equation. (States are omitted in someexamples and shown in others.)



Example Problem 4.8

When methane (often called natural gas) burns in a gas fireplace,it reacts with oxygen in the air (Figure 4.46). The products of thechemical reaction are carbon dioxide and water. Write a wordequation, skeleton equation, and balanced formula equation forthis reaction.

1. Write the word equation by placing the reactants on the leftside of the arrow and the products on the right side.methane + oxygen → carbon dioxide + water

2. To write the skeleton equation, write the symbols andchemical formulas for each of the reactants and products. Youmay need to use a periodic table, ion chart, or chart containingnames and formulas of substances. CH4 + O2 → CO2 + H2O

3. Write the balanced formula equation by adding coefficients infront of some or all of the substances in the equation, asneeded. • Count the number of atoms of each element on the

reactants side and on the products side of the skeletonequation. There are four hydrogen atoms on the reactantsside but only two hydrogen atoms on the products side.

• Guess what coefficient will balance the hydrogen atoms.For example, try placing a coefficient of 2 in front of H2O. CH4 + O2 → CO2 + 2H2O

• Count the number of atoms of each element on thereactants side and the products side. There are two oxygenatoms on the reactants side, but there are four oxygenatoms on the products side. Try placing a coefficient of 2in front of O2.CH4 + 2O2 → CO2 + 2H2O

• Counting atoms again shows there are one carbon atom,four hydrogen atoms, and four oxygen atoms on each sideof the formula equation.

The balanced formula equation is:CH4 + 2O2 → CO2 + 2H2O

Practice Problems

Balance the following skeletonequations.

1. Na + O2 → Na2O

2. HCl + Al → AlCl3 + H2

3. KClO3 → KCl + O2

Figure 4.46 Methane gas undergoesa chemical reaction when it burns.

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Example Problem 4.9

Balance the following skeleton equation.

AlBr3(s) + Cl2(g) → AlCl3(s) + Br2(g)

1. Count the number of atoms of each element in the skeletonequation.

2. Balance the number of bromine atoms by adding a coefficientof 2 in front of AlBr3 and a coefficent of 3 in front of Br2.

• Count the atoms again. For substances with a coefficient,remember to multiply the coefficient by the number ofatoms in the formula to get the total number of atoms.

• The number of aluminum atoms is no longer equal.

3. Balance the number of aluminum atoms by adding acoefficient of 2 in front of AlCl3. Count the atoms again.

• The number of chlorine atoms is no longer balanced.

4. Balance the number of chlorine atoms by adding a coefficientof 3 in front of Cl2. Count the atoms again.

The balanced chemical equation is:

2AlBr3(s) + 3Cl2(g) → 2AlCl3(s) + 3Br2(g)

Practice Problems

Balance the following skeletonequations.

1. HgO(s) → Hg(l) + O2(g)

2. Al(s) + Br2(g) → AlBr3(s)

3. Ca(s) + H2O(l) →Ca(OH)2(s) + H2(g)

Reactants Number of Atoms Products Number of Atoms

AlBr3(s) Al = 1Br = 3

AlCl3(s) Al = 1Cl = 3

Cl2(g) Cl = 2 Br2(g) Br = 2


2AlBr3(s) Al = 2 × 1 = 2Br = 2 × 3 = 6

AlCl3(s) Al = 1Cl = 3

Cl2(g) Cl = 2 3Br2(g) Br = 3 × 2 = 6


2AlBr3(s) Al = 2 × 1 = 2Br = 2 × 3 = 6

2AlCl3(s) Al = 2 × 1 = 2Cl = 2 × 3 = 6

Cl2(g) Cl = 2 3Br2(g) Br = 3 × 2 = 6


2AlBr3(s) Al = 2 × 1 = 2Br = 2 × 3 = 6

2AlCl3(s) Al = 2 × 1 = 2Cl = 2 × 3 = 6

3Cl2(g) Cl = 3 × 2 = 6 3Br2(g) Br = 3 × 2 = 6

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Strategies for Writing Skeleton EquationsWriting the correct formula for certain elements and compounds whenyou are translating word equations into skeleton equations cansometimes be difficult. Here are some tips:

• When a metal element is not in a compound with other elements,write the symbol of the element from the periodic table. Forexample, if a word description were to state “an iron nail,” itwould be translated to Fe.

• Seven common non-metal elements occur as moleculescontaining two identical atoms. These are hydrogen (H2),nitrogen (N2), oxygen (O2), fluorine (F2), chlorine (Cl2), bromine(Br2), and iodine (I2). One way to help to remember theseelements is to think of them as the “-gens”: hydrogen, nitrogen,oxygen, and the halogens (consisting of fluorine, chlorine,bromine, and iodine). For example, if a word equation were tostate “oxygen reacts with fluorine,” the skeleton equation shouldbe written O2 + F2.

• Common compounds that contain hydrogen include water (H2O),ammonia (NH3), and methane (CH4).

• Some common acids are hydrochloric acid (HCl), nitric acid(HNO3), sulphuric acid (H2SO4), and phosphoric acid (H3PO4).(You will study acids in Chapter 5.)

Example Problem 4.10 uses some of the tips.


Example Problem 4.10

Iron(II) sulphate (FeSO4) can be used to kill moss in lawns and asa nutritional supplement to treat and prevent iron deficiency.Write a formula equation, including states, in which an iron nailreacts with aqueous sulphuric acid to produce aqueous iron(II)sulphate and hydrogen gas.

1. Write the word equation by placing the reactants on the leftside of the arrow and the products on the right side.• An iron nail consists of pure iron in the solid state: Fe(s).• Aqueous sulphuric acid is a common acid (listed above):

H2SO4(aq).• Iron(II) sulphate is composed of Fe2+ and SO4

2�:FeSO4(aq).

• Hydrogen gas exists as a molecule with two identicalatoms: H2(g).

The skeleton equation is:Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g)

Practice Problems

For each of the following,translate the word equation intoa skeleton equation, showingstates. Then, balance theskeleton equation.

1. hydrogen gas + nitrogen gas →ammonia gas

2. nitrogen monoxide gas + oxygen gas →nitrogen dioxide gas

3. solid aluminum metal + aqueous nitric acid →

aqueous aluminum nitrate+ hydrogen gas

4. phosphorus trichloride gas + chlorine gas →phosphorus pentachloridegas

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181

Strategies for Writing Balanced EquationsSuccessfully balancing chemical equations can take some practice. Hereare some strategies you might try:

• Balance atoms of elements in any complicated-looking formulasfirst, and balance atoms of pure elements last.

• Never change a subscript in a formula to help make atomsbalance. Balance by placing coefficients in front of formulas only.

• Use guess-and-check to balance simple equations. Begin byplacing a coefficient where you think it might work, or just take aguess and then count atoms.

• Hydrogen atoms and/or oxygen atoms often will appear in manyor all of the formulas of the reactants and products. When this isthe case, try to balance other elements first. Balance hydrogensecond last, and oxygen last.

• You may be able to treat polyatomic ions as a unit. For example, ifNO3

– appears in the reactants and products of a skeletonequation, count the number of NO3

– groups rather than thenumber of N atoms and O atoms separately.


Aluminum fluoride (AlF3) is used in the production of aluminumfor aluminum kitchen foil. Write a balanced equation for thereaction shown by the following word equation:aluminum + fluorine → aluminum fluoride

1. Write the skeleton equation. Al + F2 → AlF3

2. Apply some of the strategies for writing balanced equations.• Al is a pure substance, so balance it last.• Do not change the subscripts in F2 or in AlF3, since this

will make these formulas incorrect.• Use guess-and-check. Place a coefficient of 3 in front of F2

and a coefficient of 2 in front of AlF3. There are now six Fatoms on each side of the equation.Al + 3F2 → 2AlF3

The number of Al atoms is no longer balanced. Correct this byplacing a coefficient of 2 in front of Al. 2Al + 3F2 → 2AlF3

3. Count the atoms of all the elements again to make sure theequation is balanced.

The balanced formula equation is:2Al + 3F2 → 2AlF3

Practice Problems

For each of the following,translate the word equationinto a skeleton equation. Then,balance the skeleton equation.

1. iron + chlorine →iron(III) chloride

2. sodium + calcium hydroxide →sodium hydroxide + calcium

3. sodium phosphate + magnesium hydroxide →magnesium phosphate +sodium hydroxide

4. sulphuric acid + nickel(III) hydroxide →nickel(III) sulphate +water


Antoine Lavoisier and Marie-Anne Paulze developed the law of conservation of mass.Find out more about thispioneering couple and the story ofhow Antoine Lavoisier died. Beginyour research at ScienceSource.

Take It Further

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Calcium phosphate is a solid called plaster of Paris and has been usedto make casts to stabilize broken bones. It can be produced in thereaction between aqueous calcium chloride and aqueous sodiumphosphate. A second product in the reaction is aqueous sodiumchloride. Write a word equation and a balanced formula equation,showing states in the formula equation.

1. Write the word equation by placing the reactants on the left sideof the arrow and the products on the right side.

Word equation:calcium chloride + sodium phosphate → calcium phosphate +

sodium chloride

2. Translate the word equation into a formula equation. Here arethe formulas as well as states:calcium chloride: CaCl2(aq)sodium phosphate: Na3PO4(aq)calcium phosphate: Ca3(PO4)2(s)sodium chloride: NaCl(aq)

Skeleton equation:CaCl2(aq) + Na3PO4(aq) → Ca3(PO4)2(s) + NaCl(aq)

3. Apply some strategies from the previous page.• Do not change any subscripts. This would make the

formulas incorrect.• Try guess-and-check.• Treat polyatomic ions as a unit. For example, balance PO4

3–

all at once.

There are two PO43– ions in the products and only one in the

reactants, so balance PO43– by placing a 2 in front of Na3PO4.

CaCl2(aq) + 2Na3PO4(aq) → Ca3(PO4)2(s) + NaCl(aq)

4. Bring Na into balance by placing a 6 in front of NaCl.

CaCl2(aq) + 2Na3PO4(aq) → Ca3(PO4)2(s) + 6NaCl(aq)

5. Finish balancing by placing a 3 in front of CaCl2. This bringsboth Ca and Cl into balance in one step.

Balanced formula equation:3CaCl2(aq) + 2Na3PO4(aq) → Ca3(PO4)2(s) + 6NaCl(aq)


Practice Problems

For each of the following, writea word equation and a balancedformula equation, showingstates in the formula equation.

1. Aqueous silver nitrate andcopper metal react toproduce aqueouscopper(II) nitrate andsilver metal.

2. Solid magnesium chlorideand aqueous potassiumphosphate react to produceaqueous potassiumchloride and solidmagnesium phosphate.

3. Hydrogen gas and carbondioxide gas react toproduce carbon monoxidegas and liquid water.

4. Solid potassium reactswith oxygen gas to producesolid potassium oxide.

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B10 Quick Lab

The flame test can be used to determine the presenceof hydrogen gas (H2(g)).

PurposeTo use the flame test to determine if hydrogen gas isproduced when solid zinc is combined withhydrochloric acid solution

Procedure

1. Your teacher will add 0.5 g of granulated zinc to a test tube, then place the test tube in the test-tube rack.

2. Your teacher will add enough HCl(aq) to the testtube to cover the zinc. Record your observations.

3. Your teacher will light a wooden splint. Holdingthe test tube with a test-tube clamp, he or she willthen insert the burning splint into the mouth ofthe test tube. This is the flame test. Record yourobservations.

Questions

4. When hydrogen gas is present during the flametest, you will hear a popping sound. Was hydrogengas produced?

5. The other product of the reaction is zinc chloride.Write a word equation and a balanced chemicalequation for this reaction.

The Flame Test (Teacher Demonstration)

B9

Everyday Chemistry

When you start your day, you probably take a shower,brush your teeth, get dressed, and fix your hair.Maybe you listen to music on your way to school.These are some of the many activities in your dailylife that involve products that were made usingchemical reactions.

For example, you might wear a shirt that does notneed to be ironed. The shirt does not wrinkle becausea chemical called a resin was applied to the fabric orbecause a chemical called a polyester was blendedwith other fibres that make up the fabric. The casingof a music player is made using chemicals known asplastics. Plastics are manufactured using a number ofchemical reactions.

1. In your group, brainstorm ways that you usechemicals or products made using chemicalreactions. Think of and list as many ways as you can.

2. Choose at least five items from your list. Foreach item, provide further information orexamples. You might need to do some research.You can start your research at ScienceSource.

3. Organize and display your work using a methodof your choice or as directed by your teacher.


CAUTION• Tie back loose hair or clothing.

• 0.5 g of granulatedzinc, Zn(s)

• 1 test tube

• 1 test-tube rack

• test-tube clamp

• 5 mL of 3Mhydrochloric acid, HCl(aq)

• matches

• wooden splint


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B11 Inquiry Activity

In 1789, Antoine and Marie-Anne Lavoisier performeda series of chemical experiments in a containerdesigned to keep all the products of a chemicalreaction inside. These experiments led to thediscovery of the law of conservation of mass. In thisactivity, you will make a prediction and then observewhat happens to mass during two chemical reactions,one that takes place in a sealed system and one thattakes place in an open system.

QuestionDoes the total mass change during a chemicalreaction?

Procedure

Part 1 — A Chemical Reaction Inside aSealed System

1. Read steps 2 to 8, and then write a predictionabout what will happen to the total mass of theflask and its contents when the chemicals react.

2. Test that the equipment fits together. Carefullyslide a small test tube into the Erlenmeyer flask.Seal the flask with a rubber stopper. Check thatthe stopper does not fall out when you turn theapparatus upside down (Figure 4.47).

3. Take the test tube out, and place it in the test-tuberack for safekeeping.

4. With the graduated cylinder, measure 25 mL ofcalcium chloride solution and then pour it into theErlenmeyer flask. Wipe the outside of the flask tomake sure it is dry. Set it aside.

5. Fill the test tube about half full with sodiumcarbonate solution. Wipe the outside of the testtube to make sure it is dry. Place the test tube inthe 50-mL beaker

6. Carefully slide the filled test tube into theErlenmeyer flask. Seal the flask with the rubberstopper, ensuring that the two solutions do notmix. Measure and record the total mass of thesealed assembly.

7. Tip the assembly so that the two liquids mix. Keepyour thumb on the rubber stopper so that itremains in place and does not leak. Observe thechemical reaction. Record your observations.

8. Measure the mass of the total assembly again,and record it.

9. Check your results against your prediction. Ifnecessary, revise your prediction.


Does Mass Change During Chemical Reactions?

SKILLS YOU WILL USE■ Evaluating reliability of data and

information■ Identifying sources of error

• Erlenmeyer flask withtight-fitting stopper

• small test tube

• test-tube rack

• balance


• calcium chloridesolution, CaCl2(aq)

• sodium carbonatesolution, Na2CO3(aq)

• scoopula

• sodium hydrogencarbonate, NaHCO3(s)

• 50-mL beaker

• hydrochloric acidsolution, HCl(aq)



Figure 4.47 Ensure the test tube is sealed in the flask.

Key ActivityD

I

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B11 Inquiry Activity (continued)

Part 2 — A Chemical Reaction Inside anOpen System

11. Read steps 12 to 16, and then write a predictionabout what will happen to the total mass of theflask and its contents when the chemicals react.

12. Using the balance and the scoopula, measure 5 gof sodium hydrogen carbonate powder into a dry50-mL beaker.

13. Fill a small test tube about half full withhydrochloric acid solution. Wipe the outside of thetest tube to make sure it is dry.

14. Carefully slide the test tube into the beaker,ensuring that the sodium hydrogen carbonatepowder does not mix with the hydrochloric acidsolution. Measure and record the total mass of theassembly.

15. Empty the contents of the test tube into thebeaker. Record your observations.

16. Measure and record the mass of the beaker, testtube, and mixed solutions.

17. Check your results against your prediction. Ifnecessary, revise your prediction.


19. In your notebook, draw a table using the headingsshown in Table 4.18. Collect and record the classdata for Parts 1 and 2 in your table.


20. What evidence was there that a chemical reactionoccurred in Part 1 and/or Part 2?

21. For your group, how did the total mass aftermixing compare with the total mass before mixing,in both Part 1 and Part 2?

22. How did your observations of the overall changesin mass compare with your predictions?

23. Using the data for Part 1 and Part 2 from theentire class, compare the total mass after thechemical reactions had occurred with the totalmass before mixing.

Skill Practice

24. How precisely were you able to measure masseach time (i.e., to how many places after thedecimal point were you able to read your massmeasurements)?

25. Suggest some possible causes for errors inmeasurement for this activity.

Forming Conclusions

26. Using the class results for both parts of thisactivity, state a conclusion about changes in massin a sealed system versus an open system. Forexample, you might calculate the average changein mass for all groups for each part.

27.Do the results of this activity support the law ofconservation of mass? Provide reasons for youranswer.

Group # Part 1 — Sealed System Part 2 — Open System

Total MassBefore (g)

Total MassAfter (g)

Change inMass (g)

Total MassBefore (g)

Total MassAfter (g)

Change inMass (g)

Table 4.18 Does Mass Change During Chemical Reactions?

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QuestionWhat kinds of changes can be observed to occurduring chemical reactions?

ProcedurePart 1 — Iron and Copper(II) Chloride

1. Fill a 50-mL beaker half full with 1 M copper(II)chloride solution. Observe the solution.

2. Gently place a clean iron nail into the copper(II)chloride solution, making sure the head of the nailremains dry and out of the solution. Every fewminutes, lift the nail partly out of the solution andobserve. Gently replace the nail to allow it tocontinue to react.

3. After 15 min, record all your observations.

Part 2 — Calcium Chloride and SodiumCarbonate

4. Fill a test tube one-third full with 1 M calciumchloride solution. Fill a second test tube one-thirdfull with 1 M sodium carbonate solution.

5. Pour the contents of one test tube into the other,and observe.

6. Set the test tube in the test-tube rack, and observeagain after 10 min. Record your observations.

Part 3 — Hydrogen Peroxide Decomposition

7. Carefully pour 6% hydrogen peroxide solution intoa test tube to a depth of about 2 cm. Add 2 dropsof liquid dish soap to the solution. Set the testtube into the test-tube rack.

8. Using a scoopula, get a pea-sized amount ofpotassium iodide powder and drop it into the testtube. Observe. (Note: KI helps this reaction goquickly but is NOT considered a reactant.)

9. Light a wooden splint with a match, and blow outthe flame, leaving only a glowing ember. Place theglowing splint into the top of the test tube and alsointo some soap bubbles that are present. Observe.Repeat several times. Record your observations.



11. Write a skeleton equation for each of the threechemical reactions in this activity. The products ofthe chemical reactions are as follows:

Part 1: iron(II) chloride and copperPart 2: sodium chloride and calcium carbonatePart 3: oxygen gas and water

Skill Practice

12. Many furnaces burn natural gas. Is burningnatural gas a physical change or a chemicalchange? Justify your conclusion.

Forming Conclusions

13. Write a summary that answers the question at thebeginning of this activity.

Observing Chemical Change

SKILLS YOU WILL USE■ Observing and recording

observations ■ Drawing conclusions

CAUTION• Tie back loose hair or clothing.

• 50-mL beaker

• 1 M copper(II) chloride solution,CuCl2(aq)

• iron nail, Fe(s)

• 3 test tubes

• 1 M calcium chloride solution,CaCl2(aq)

• 1 M sodium carbonate solution,Na2CO3(aq)

• test-tube rack

• 6% hydrogen peroxide solution,H2O2(aq)

• liquid dish soap

• scoopula

• potassium iodide, KI(s)

• wooden splints

• matches



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Key Concept Review


2. Use the following chemical equation toexplain these terms: reactants, products, stateof matter, symbols, formulas, subscripts,coefficients.Zn(s) + 2HCl(s) → ZnCl2(aq) + H2(g)

3. During a forest fire, like the one shown in thephoto, large trees weighing thousands ofkilograms werereduced toonly a fewkilograms ofash. Whathappened tothe mass of thetrees whenthey burned?

Connect Your Understanding4. Write a word equation and a balanced

formula equation, including states, for each ofthe following reactions. Hint: Remember touse the correct formula for elements thatform a diatomic molecule.

(a) Solid aluminum metal combines withfluorine gas to produce solid aluminumfluoride.

(b) Potassium metal combines with oxygengas to produce solid potassium oxide.

(c) Lithium sulphate combines with bariumchloride and yields solid barium sulphateand aqueous lithium chloride. Both of thereactants are dissolved in water.

(d) Aluminum chloride combines withsodium carbonate to produce aluminumcarbonate and sodium chloride. Thealuminum carbonate is a solid at thebottom of the container. The other threecompounds are all aqueous.

5. Balance the following skeleton equations.

(a) Al(s) + F2(g) → AlF3(s)

(b) K(s) + O2(g) → K2O(s)

(c) C6H12O6(s) + O2(g) →

CO2(g) + H2O(l)

(d) H2SO4(aq) + NaOH(s) →

Na2SO4(aq) + H2O(l)

(e) Mg(CH3COO)2(aq) + AgNO3(aq) →

Mg(NO3)2(aq) + AgCH3COO(s)

(f) H2O2(aq) → O2(g) + H2O(l)

(g) HCl(aq) + Ba(OH)2(aq) →

BaCl2(aq) + H2O(l)

6. For each of the following, write a wordequation and a balanced formula equation.Hint: Remember to use the correct formulafor diatomic elements.

(a) Solid calcium metal combines withoxygen gas in the air to produce solidcalcium oxide.

(b) Propane gas (C3H8) combines withoxygen gas in the air to produce carbondioxide gas and water vapour.

(c) Fluorine gas combines with aqueouspotassium chloride. The chemical reactionproduces aqueous potassium fluoride andchlorine gas.

Reflection7. Using a poster, Web page, or another method

of your choosing, summarize what you havelearned about balancing chemical equations.




Question 3

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Dr. Robert D. Singer is a professor in and chair of thechemistry department at St. Mary’s University inHalifax, Nova Scotia (Figure 4.48). One of hisresearch interests is in the area of green chemistry.

Green chemistry is a new area of research. Thegoal of green chemistry is to protect theenvironment by inventing chemicals and chemicalprocesses that do not pollute. This is a lot lessharmful to our environment than cleaning uppollution after it has already occurred. Greenchemistry also looks for ways to use renewablestarting materials and to reuse any wastes.

Dr. Singer is a member of a group of scientists,industrial leaders, and environmentalists called theGreen Chemistry Network. Members of this grouppromote and teach green chemistry in industry,business, universities, and schools.

Dr. Singer and the members of his research groupare looking for ways to replace the use of chemicalscalled volatile organic compounds (VOCs) in certainindustrial processes. VOCs produce harmful fumesand can easily catch fire. You may have heard aboutlow-VOC or no-VOC paints (Figure 4.49). These arean example of a green chemistry success story.

Dr. Singer has found that some VOCs can bereplaced with ionic liquids. Ionic liquids do notproduce fumes and will not burn. Since they do notrelease harmful fumes, they could make workplacessafer for people who handle and use chemicals.

Questions

1. What is Dr. Singer’s contribution to the healthof our environment?

2. ScienceSource The Green Chemistry Networkhas outlined 12 principles of green chemistry.Conduct research to find out what these 12 principles of green chemistry are.

CAREERS in ScienceInvestigating


Great CANADIANS in Science Dr. Robert D. Singer

Figure 4.49 Low-VOC and no-VOC paints are safer to use andbetter for the environment.

Figure 4.48 Dr. Singer and his research group focus onmany aspects of green chemistry.

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What do plastic food wrap, automobile parts, andsneakers have in common (Figure 4.50)? All theseproducts, and many others that you use every day,are made with a type of chemical called a polymer.Polymer chemists are scientists who study andcreate new polymers.

A polymer is a chemical compound that iscomposed of a large number of smaller, identicalunits that are joined together to form one largemolecule. Polymers may be natural or synthetic. Forexample, starch is a natural polymer made up ofmany sucrose molecules joined together. Vinyl is anexample of a synthetic polymer is found in manyproducts, including home siding, electricalcomponents, and medical products.

Polymer chemists are involved in creating newpolymers and/or finding new uses for the polymerswe already have. Therefore, a polymer chemist’s jobinvolves some aspect of analyzing, synthesizing,purifying, modifying, and characterizing differentpolymers. She or he may be involved in ensuring thatsome or all of the stages of production of polymersmeet quality control standards. A polymer chemistalso might investigate the physical and chemicalproperties of polymers. Some polymer chemists areemployed as technical consultants.

Most polymer chemists are employees who workfor a private company or in a university or agovernment laboratory. Depending on their trainingand experience, they may supervise other chemistsand/or technicians and technologists. Polymerchemists often work in collaboration with otherexperts, such as engineers. Working as a polymerchemist involves a higher-than-average danger ofexposure to dangerous chemicals, but these dangersare reduced by following good safety practices.

At a minimum, a bachelor’s degree in chemistry isneeded to work in this field. To be able to enter into abachelor’s degree program in chemistry, a personmust have successfully completed at least two grade 12 mathematics courses, a grade 12 chemistrycourse, at least two other grade 12 science courses,and a grade 12 English course. Universities oftenrequire specific courses and final grades. A personwith a bachelor’s degree in chemistry is likely to be ateacher or to work in the polymer industry as atechnician or a sales person. You will need a master’sor a doctorate degree to find work conductingresearch in industry or at a university or governmentlaboratory. Anyone who works in this field should lovelearning, since he or she must always keep up withnew advances in polymer chemistry.

Questions

1. Write a job description for a polymer chemist inthe form of an advertisement for a position at achemical company.

2. ScienceSource Research what universitycourses you would need to take to become apolymer chemist.

Science in My FUTURE Polymer Chemist


Figure 4.50 Polymers are used in the materials thatmake up the soles and tops of many sneakers and othersports shoes.

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190 UNIT B

Key Concept Review1. Name two properties possessed by all forms

of matter.

2. Identify two kinds of pure substances andthree kinds of mixtures.

3. Explain the difference between ahomogeneous mixture and a heterogeneousmixture, giving an example of each.

4. Identify the three subatomic particles, theirelectric charge, and location in an atom.

5. What are the two main types of compounds,and what are the names of the chemicalbonds involved in each?

6. Name each of the following ions: (a) Na+ (b) Ca2+ (c) Fe3+ (d) F– (e) O2–

7. Suppose that a friend tells you that a balancedchemical equation involves only coefficientsand chemical symbols. Would your friend becorrect? If not, what else is needed?

8. Name all seven elements that form diatomicmolecules. Provide the correct symbol foreach molecule.

Connect Your Understanding9. A group of students wanted to test the law of

conservation of mass. They carefully weigheda test tube and two dissolved compoundsprovided by their teacher. They then carefullypoured both solutions into a test tube. Afterseveral minutes, the chemical reaction wascomplete (pictured in the next column). Thestudents then weighed the test tube and itscontents and found that the mass haddecreased by 0.27 g. The students concludedthe chemical reaction caused a loss of mass.

(a) Do you agree with the students’conclusion? Explain your answer.

(b) Suggest how the students could revisetheir procedure in doing another trial.

10. A friend tells you that only one possiblecompound can be made from the elementshydrogen and oxygen. Use the chemicalformulas provided in this chapter to respondto your friend’s statement.

11. State the similarities and differences between:

(a) an element and a compound

(b) an atom and an ion

12. What are the differences between hydrogen(H) and hydrogen gas (H2)?

13. What is the total number of atoms in onemolecule of white sugar (sucrose),C12H22O11? Show how you calculated thisanswer.

14. Write the symbol for the ion formed by eachof following elements.

(a) oxygen

(b) bromine

(c) sulphur

(d) calcium

(e) copper(I)

a

a

k

t

t

a

t

k

k

a

k

k

k

k

k

ACHIEVEMENT CHART CATEGORIES

Knowledge and understanding Thinking and investigation

Communication Applicationac

tk

4 CHAPTER REVIEW

Question 9

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15. Write the symbol for the following polyatomicions.

(a) ammonium

(b) carbonate

(c) hydrogen carbonate

(d) phosphate

16. Name each ionic compound.

(a) Na3N (e) PdO2

(b) CaF2 (f) KMnO4

(c) Al(OH)3 (g) (NH4)3PO4

(d) FeCl2 (h) Cr(NO3)2

17. Write the formula of each ionic compound.

(a) potassium iodide

(b) strontium nitride

(c) manganese(IV) chloride

(d) tin(II) sulphide

(e) magnesium hydroxide

(f) zinc phosphate

(g) silver oxide

(h) ammonium nitrate

18. Suppose that Canadian scientists discovered anew metal element, called ontarium (symbolOn). Ontarium has two valence electrons.Write the chemical formula for the followingcompounds of ontarium:

(a) ontarium oxide

(b) ontarium chloride

(c) ontarium phosphate

19. Write the formula or name for each molecularcompound.

(a) dinitrogen trioxide

(b) carbon monoxide

(c) sulphur hexafluoride

(d) PBr5

(e) CCl4(f) NBr3

20. Balance the following skeleton equations.

(a) Li(s) + F2(g) → LiF(s)

(b) Be(s) + O2(g) → BeO(s)

(c) HCl(aq) + NaOH(s) →

NaCl(aq) + H2O(l)

(d) Ca(CH3COO)2(aq) + AgNO3(aq) →

Ca(NO3)2(aq) + AgCH3COO(s)

(e) NBr3(l) → N2(g) + Br2(g)

(f) HF(aq) + Ba(OH)2(aq) →

BaF2(aq) + H2O(l)

Reflection21. Describe three or more new ideas about

elements that you have learned in thischapter. Then, list three or more questionsyou have about these new ideas or any relatedtopic. c

a

a

a

a

a

a

Reflect and Evaluate

Use a two-column chart to summarize how you were

able to determine important ideas in this chapter. In

the first column, list words, text features, and

purpose, leaving several lines between each item. In

the second column, record examples from the text.

With a partner, compare charts and explain how

each feature helped you to understand important

ideas.

After Reading

Unit Task Link

In the Unit Task, you will be using the following

substances in order to produce and observe

chemical reactions. Classify each of the following as

an element, an ionic compound, or a molecular

compound, and name each one: Mg, MgSO4, CuCl2,

Na2CO3, HCl(aq), Fe.

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5 Acids and bases are important to ourhealth, industries, and environment.

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Acids and bases are important to our health, industry, and environment. 193

In order to properly maintain a swimming pool, youneed to understand acids and bases.


• use appropriate terminology related to chemical reactions

• plan and conduct an investigation to classify some commonsubstances as acidic, basic, or neutral


• analyze, on the basis of research, various safety andenvironmental issues associated with chemical reactions andtheir reactants and/or products

• analyze how an understanding of the properties of chemicalsubstances and their reactions can be applied to solveenvironmental challenges

• describe the process of acid-base neutralization

• describe how the pH scale is used to classify solutions asacidic, basic, or neutral

• identify acids, using the periodic table and a list of the mostcommon polyatomic ions, and write their formulas

Why It Is ImportantWith the exception of pure water, almost every liquid youencounter in daily life is an acid or a base. Acids play importantroles in our bodies, and many foods are acidic. Both acids andbases are used in industrial processes. Since acids and basescan also cause harm to living things and the environment, it isimportant to know how to use them safely.

Monitoring Comprehension

Good readers constantly monitor their understanding of what

they are reading. They note areas of difficulty and know ways

to fix up meaning so that they can continue to read without

getting frustrated. Preview this chapter, and then predict

topics you think you will understand and topics where you

may have to use fix-up strategies. List some ways you already

know to fix up meaning.

Key Terms

• acid • acid-base indicator • base • neutral

• neutralization • pH • pH scale

Before Reading

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Acids, Bases, and Your BodyAcids and bases are compounds with particular properties. Members ofthese two classes of compounds play many different roles in thefunctioning of your body.

Some acids are harmful to your body. For example, the cells in yourbody are fuelled by the breakdown of molecules of glucose (Figure 5.1).The products of this process usually include carbon dioxide gas(CO2(g)). This carbon dioxide gas dissolves in the water in your bloodand forms carbonic acid (H2CO3(aq)). A build-up of this acid in theblood would be harmful, so your body converts the carbonic acid to ahydrogen ion (H+) and a hydrogen carbonate ion (HCO3

–). These ionsare then transported in the blood without harming the body.

Other acids are essential to your body functions. One such essentialacid is deoxyribonucleic acid (DNA). DNA is a complex molecule that is responsible for passing on inherited characteristics, such as haircolour, from one generation to the next.

Similarly, some bases produced by your body are harmful and some are helpful. An example of a harmful base is ammonia (NH3).Your body produces ammonia as a waste product of the breakdown ofsome types of food. Ammonia is toxic to humans, so your body convertsit to urea ((NH2)2CO). Urea is not toxic and is removed from your bodyin your urine.


• The pH scale is used to classifyaqueous solutions as acidic,basic, or neutral.

• Acids and bases react with pH indicators.

• Acids have a pH less than 7.

• Bases have a pH greater than 7.

• A neutral solution has a pH of 7.

Acids and Bases

Figure 5.1 During exercise and in its day-to-day functioning, your body gets much of theenergy it needs from the breakdown of glucose. The process by which glucose is broken downproduces carbon dioxide gas, which dissolves in your blood and forms an acid.

5.1

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195Acids and bases are important to our health, industry, and environment.

Digestion is a process that breaks down your food intocomponents that your body can use for energy. The digestive processbegins with the saliva in your mouth (Figure 5.2). The saliva of ahealthy person is usually basic. Your stomach contains hydrochloricacid (HCl), which helps your stomach to break down your food intosmaller particles. However, hydrochloric acid can also damage thecells of your body. The lining of your stomach is protected from acidby a thick layer of mucus, but the rest of your digestive system lacksa protective layer. An organ called the pancreas produces a basecalled sodium hydrogen carbonate (NaHCO3). This base counteractsthe hydrochloric acid, which protects the rest of your digestivesystem. The digestion of fats depends on the production of anotherbase, called bile. Bile is produced by the liver.

B13 Quick Lab

What Do You Know about Acids and Bases?

Acids and bases are found in many of the foods weeat and the products we use. For example, grapescontain an acid and some soaps are made using abase (Figure 5.3 and Figure 5.4). In this activity, youwill identify foods and products that are acids orbases or that contain an acid or a base.

PurposeTo brainstorm a list of foods and household productsthat are acids and bases or that contain an acid or abase

Procedure

1. Working with a partner or in a group, brainstormfoods and products that you think are acids orbases or that contain an acid or a base.

2. Record your list in a T-chart with two columns.

3. Share your T-chart with your classmates. Add anynew ideas from their T-charts to yours.

Questions

4. What criteria did you use to predict if a food orproduct was an acid or a base?

5. Compare and contrast the criteria you used withthose used by your classmates.

mouth(produces saliva,

usually basic)

esophagus

stomach(produces HCl,

an acid)

pancreas(produces NaHCO3,

a base)

liver(produces bile,

a base)

Figure 5.2 A simplified drawing of some ofthe organs involved in human digestion

Figure 5.3 Grapes contain tartaric acid.

Figure 5.4 The base potassiumhydroxide (KOH) is used in producingsoft and liquid soaps.

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During Reading

Listen to Your Inner Voice

Good readers are conscious of an

inner voice that tells them when

they understand and when they

do not understand what they are

reading. Choose a paragraph and,

while you are reading, be

conscious of that inner voice that

tells you what you understand and

where you may need to fix up

meaning.

Identifying Acids and BasesThousands of years ago in Asia and Europe, early chemists tried toclassify the substances they found in nature. One property they usedwas taste. This property accurately distinguished acids from bases: acidstaste sour, while bases taste bitter. Tasting unknown substances is notsafe, and you should never taste an unknown substance to identify it orits properties.

pH and the pH ScaleToday, you can determine if a substance is an acid or a base bymeasuring its pH. You have probably heard the term “pH” before. It isused in advertising (e.g., pH-balanced shampoo), in the careinstructions for pools (pH of the pool water), and even in gardening(soil pH). The pH measurement is related to the number of hydrogenions (H+) that are in a solution. The abbreviation “pH” stands forpower (or potential) of hydrogen. The pH scale is a number scale thatindicates how acidic or basic a solution is (Figure 5.5).

The pH of a substance can be determined only when it is inaqueous solution (i.e., dissolved in water). Looking at the pH scale inFigure 5.5, you see that pure water has a pH of 7. Any substance with apH of 7 when it is in aqueous solution is neutral. A neutral substance,such as pure water, is neither an acid nor a base.

An acid is a substance that has a pH less than 7 when it is inaqueous solution. The more acidic a substance is, the lower the pH. Forexample, lemon juice is an aqueous solution of a number of chemicals,including citric acid and ascorbic acid (vitamin C). Lemon juice has apH of 2, and so it is moderately acidic.


Figure 5.5 The pH scale is used to identify how acidic or basic an aqueous solution is.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14moreacidic

2.0lemon juice

4.2 tomatoes

6.0 milk

neutral

8.2 baking soda

10 toothpaste

12ammonia

13.8 drain

cleaner

morebasic

0.5battery acid

7.0pure water

5.0acid rain

5.6 normal

rain8.0

seawater

2.2vinegar

1.0stomach acid

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A base is a substance that has a pH greater than 7 when it is inaqueous solution. The more basic a substance is, the higher the pH.Sodium hydrogen carbonate is commonly called baking soda and is used to make a number of foods. When sodium hydrogen carbonate isdissolved in water, the resulting solution is basic.

One unit of change on the pH scale represents a 10 times change inhow acidic or basic a solution is. For example, the hydrochloric acid inyour stomach has a pH of 1. This is 10 times more acidic than lemonjuice (pH 2). The closer the pH of a solution is to 0, the more acidic itis. The closer the pH of a solution is to 14, the more basic it is.

Acid-Base IndicatorsThere are a number of ways of determining the pH of a solution. Oneway is to use an acid-base indicator. An acid-base indicator is anysubstance that changes colour in the presence of an acid or a base.

The most widely known acid-base indicator is litmus. Litmus is aplant extract and can be blue or red (pink). Litmus paper is made fromblue or red litmus dried onto strips of filter paper. Red litmus paperturns blue when it is dipped into a basic solution. Blue litmus paperturns red when it is dipped in an acidic solution. Neither litmus paperchanges colour in a neutral solution. Figure 5.6 shows a memory aid forremembering these colour changes.

It would be impossible to determine the pH of all solutions using justone indicator, such as litmus. A universal indicator is a mixture ofchemicals that changes colour through a wide range of pH values.

Paper strips called pH paper are embedded with a universalindicator. When pH paper is dipped in a solution, one or more of theseindicators will change colour. You can then determine the pH of thesolution by comparing the colour of the dipped strip with a standardcolour chart. An even more precise way of determining pH is to use apH meter (Figure 5.7).


ACIDRED

BASEBLUE

Figure 5.6 This diagram shows a trickto help remember what happens tothe colour of litmus paper whenplaced in acids and bases.

Figure 5.7 A pH meter can preciselymeasure the pH of an acidic or basicsolution.

Learning Checkpoint

1. Is a solution with a pH of 11 acidic or basic?

2. Is a solution with a pH of 5 acidic or basic?

3. What is the pH of pure water?

4. Could you determine a specific pH value for a solution using blue litmus paper?

Explain.

5. What is the advantage of using a universal indicator?

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Properties of Acids and BasesThe properties of acids and bases make them useful in many differentways. For example, sulphuric acid is used in automobile batteriesbecause it is a good conductor of electricity. Table 5.1 compares theproperties of acids and bases.


Acids Bases

Similarities

dissolve in water dissolve in water

conduct electricity in aqueous solution conduct electricity in aqueous solution

can irritate or burn skin can irritate or burn skin

Differences

taste sour taste bitter

do not feel slippery feel slippery

pH less than 7 pH greater than 7

turn blue litmus paper red turn red litmus paper blue

release hydrogen ions (H+) in aqueoussolution

release hydroxide ions (OH–) in aqueoussolution

corrode metals do not corrode metals

react with metals to produce a compoundand hydrogen gas

do not react with metals to produce acompound and hydrogen gas

Table 5.1 Comparison of the Properties of Acids and Bases

Figure 5.8 Brook trout cannot survivein water with a pH lower than 4.1.

Acids and bases can sometimes be harmful. For instance, if water inthe environment becomes too acidic or too basic, it can harm the livingorganisms in it (Figure 5.8). Solutions that are very acidic or very basiccan be quite dangerous. The sulphuric acid in an automobile batteryhas a pH of 0.5, so it is very acidic. If battery acid were to touch yourskin, it would quickly cause severe burns.

Identifying and Naming AcidsYou can identify an acid from its name or from its chemical formula.Usually, the name of an acid ends with the word “acid.” If you are giventhe chemical formula of a substance, you know that it is an acid if:

• the chemical formula starts with H (the symbol for a hydrogenatom) OR

• the chemical formula ends with COOH (the formula for acarboxyl polyatomic ion)

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For example, HF(aq) is an acid because it starts with an H. One waythat hydrofluoric acid (HF) is used is in etching glass (Figure 5.9).CH3COOH(aq) is an acid because it ends with COOH. The name of thisacid is acetic acid. You have probably used a diluted solution of aceticacid in your food. Diluted CH3COOH(aq) is vinegar.

Naming AcidsThere are two rules for naming acids that you will use in this sciencecourse. You may learn additional rules for other types of acids in afuture chemistry course.

When the chemical formula of an acid starts with H and has onlyone other non-metallic element, it is named according to the stepsshown in Table 5.2.

Some acids contain a polyatomic ion. When the polyatomic ion inan acid contains an oxygen atom (O) and its name ends in “ate”, theacid can be named by the steps shown in Table 5.3. For example,H2SO4(aq) is an acid that contains the polyatomic ion sulphate (SO4

2–).Sulphuric acid has many uses, such as in dyeing clothing (Figure 5.10).The sulphate ion contains an oxygen atom, and its name ends in “ate.”However, the acid HNO3(aq) is called nitric acid, not “nitrogenic acid.”


Figure 5.9 This beautiful etched glasswindow was made using hydrofluoricacid (HF).


StepExamples

HCl(aq) HF(aq)

1. Start with the prefix “hydro.” hydro hydro

2. To the first part of the name of the non-metallicelement, add the suffix “ic” and the word “acid.”

hydrochloricacid

hydrofluoricacid

Table 5.2 Naming Acids That Contain Hydrogen and a Non-Metallic Element

StepExamples

H2SO4(aq) H3PO4(aq)

1. Start with the name of the element in thepolyatomic ion that is not oxygen.

sulphur phosphorus

2. Add the suffix “ic” and the word “acid.” sulphuric acid phosphoricacid

Table 5.3 Naming Acids That Contain a Polyatomic Ion with an Oxygen Atomand a Name Ending in “ate”

Figure 5.10 Sulphuric acid is used toproduce the colourful dyes in theseclothes.

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Many acids have common names. Table 5.4 shows you theformulas, chemical names, and common names of some acids and someways in which these acids are used.


Chemical Formula Chemical Name Common Name(s) Uses

HCl(aq) hydrochloric acid muriatic acid,stomach acid

cleaning concrete,making other chemicals

H2SO4(aq) sulphuric acid battery acid car batteries, makingfertilizer, manufacturing

HCOOH(aq) methanoic acid formic acid dyeing wool, tanningleather

CH3COOH(aq) ethanoic acid acetic acid diluted to make vinegar,making plastic, addedto foods for flavour

Table 5.4 Formulas, Chemical and Common Names, and Uses of Some Acids

Learning Checkpoint

1. State the common names of the following acids.

(a) HCl(aq)

(b) HNO3(aq)

(c) CH3COOH(aq)

2. Name the polyatomic ion in each of the following acids.

(a) sulphuric acid

(b) nitric acid

Identifying and Naming BasesA base can also be identified from its name or its chemical formula. Asubstance is a base if its name begins with the name of a metallic ionand ends with the word “hydroxide.” A substance is also a base if:

• the chemical formula starts with a metallic ion or with theammonium ion NH4

+ AND

• the chemical formula ends with OH (called a hydroxyl group)

For example, NaOH(s) starts with the metallic ion sodium (Na+)and ends with OH–. Similarly, KOH(s) starts with the metallic ionpotassium (K+) and ends with OH–. NH4OH(aq) starts with theammonium ion and ends with OH–. All these compounds are bases.

Sodium hydroxide (NaOH) is a base you may know about. The baseis commonly found in drain cleaners and oven cleaners (Figure 5.11).Sodium hydroxide is a white solid that easily dissolves in water. Theresulting solution is very basic and corrosive.

Figure 5.11 This oven cleanercontains sodium hydroxide and is verybasic. This warning label shows thesymbol for corrosive chemicals. Youshould always wear gloves whenworking with corrosive substances.

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Naming BasesThe name of a base can be determined from its chemical formula byfollowing the steps shown in Table 5.5. Notice that all bases arefollowed by the word “hydroxide.”

Like acids, many bases also have common names. A substance thatis a base may be called an alkali or said to be alkaline. Table 5.6 showsthe formulas, chemical names, and common names of some bases andsome ways in which they are used.

StepExamples

KOH(aq) NH4OH(aq)

1. Write the name of the positively charged metallicion that is at the beginning of the chemicalformula. This step remains the same if thepositively charged ion is a polyatomic ion.

potassium ammonium

2. Add the word “hydroxide.” potassiumhydroxide

ammoniumhydroxide

Table 5.5 Naming Bases

Chemical Formula Chemical Name Common Name Uses

NaOH(s) sodiumhydroxide

caustic soda cleaning drains; making soap, plastic, and textiles; controllingpollution

NH4OH(aq) ammoniumhydroxide

ammonia solution cleaning windows; making dyes, plastic, and glass; controllingpollution

Ca(OH)2(s) calciumhydroxide

slaked or hydratedlime

making glass, cement, and steel; correcting acidic soil; removinghair; making baby formula

Mg(OH)2(s) magnesiumhydroxide

milk of magnesia treating indigestion, bleaching clothes, treating wastewater, makingarticles fire resistant

Table 5.6 Formulas, Chemical Names, Common Names, and Uses of Several Important Bases

Learning Checkpoint

1. Name the following bases.

(a) KOH(s)

(b) Ca(OH)2(s)

(c) Mg(OH)2(s)

(d) NH4OH(aq)

2. Which polyatomic group is found at the end of the chemical formula for most

bases?

Deoxyribonucleic acid (DNA) isfound in every cell of your body.The three-dimensional structure ofthis acid remained a mystery formany years. You can solve themystery for yourself. Begin yourresearch at ScienceSource.

Take It Further

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B14 Quick Lab

PurposeTo determine which types of household liquids areacidic and which are basic

Procedure

1. In your notebook, make a table similar to Table 5.7. Add the name of each liquid you will be testing to your table.

2. Pour a small sample of one of the liquids into asmall container. Dip a strip of pH paper (Figure 5.12) into the liquid.

3. Compare the colour of the pH paper strip to thepH colour standards on the pH paper package.Record the approximate pH in your table. Classifyeach liquid as acidic, basic, or neutral.

4. Place the used pH paper strip on a paper towel.

5. Repeat steps 2 to 4 for the remaining liquids.

6. Obtain the three liquids identified only as “Dishsoap,” “Soft drink,” and “Orange juice.” Basedon your results so far, predict whether each isacidic, basic, or neutral, and predict theapproximate pH of each.

7. Measure the pH of each of the three liquids usingthe procedure in steps 2 to 4. Compare yourmeasurements to the predictions you made instep 6.


Question

9. Sort the liquids you tested according to their use.For example, some are cleaning products andsome are foods. Which types of liquids wereacids? Which were bases?

The pH of Household Liquids

• samples of common household liquids

• small containers, such as petri dishes

• pH paper

• paper towels

• samples of liquids labelled “Dish soap,” “Soft drink,” and “Orange juice”


Figure 5.12 When dipped in an acid, pH paper turns red topinkish. When dipped in a base, it turns dark blue to green.

Table 5.7 Approximate pH of Household Liquids

Name ofLiquid

pH Value Acidic, Basic, orNeutral

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Key Concept Review1. What is an acid? Name several acids.

2. What is a base? Name several bases.

3. Use the chemical or physical propertiesidentified below to classify each solution as acidic, basic, or neutral.

(a) feels slippery and conducts electricity

(b) Red litmus stays red, and blue litmus turns red.

(c) tastes sour and feels wet but not slippery

(d) has a pH of 3 and turns blue litmus red

(e) conducts electricity and has a pH of 9

4. Would a solution that contains calcium hydroxide (Ca(OH)2) dissolved in water be acidic, basic, or neither? Explainhow you know.

5. How are acids similar to bases? How are acidsdifferent from bases? (Hint: Check Table 5.1on page 198.)

6. What is an acid-base indicator?

7. From the following formulas, decide whetherthe solution is acidic, basic, or salt.

(a) KOH(aq)

(b) NaCl(aq)

(c) HCl(aq)

(d) C6H5COOH(aq)

8. State the name or the formula for each of thefollowing substances. Then indicate if it is anacid or a base.

(a) aqueous hydrogen nitrate

(b) cesium hydroxide

(c) aqueous hydrogen chloride

(d) phosphoric acid

(e) KOH(aq)

(f) H2SO4(aq)

9. Write the chemical formulas for the following bases.

(a) magnesium hydroxide

(b) potassium hydroxide

(c) aluminum hydroxide

Connect Your Understanding10. Would you expect to find acids or bases inside

an alkaline battery? Why?

11. One strip of red litmus paper was dipped intoan acidic solution of lemon juice, and asecond strip was dipped into a basic solutionof baking soda. Which of the two stripsshown in the photograph below was dipped inthe lemon juice solution and which into thesolution of baking soda?

12. Household (white) vinegar contains 5 percentacetic acid. Suggest why 100 percent aceticacid is not used as a food.

13. Why is a universal indicator more useful thanlitmus paper for measuring pH in someapplications?

14. Neatly draw a two-column chart. Label thecolumns “Uses for Acids” and “Uses forBases.” Then, use the information in thissection to complete the chart.

Reflection15. What would you like to know more about

concerning acids and bases?




Question 11

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pH and PlantsOntario farmers produce a wide variety of fruits, vegetables, and othercrops (Figure 5.13). Growing plants for a living can be risky. Manyfactors can affect the success of a crop, from weather conditions to thenutrient content of the soil. Soil pH is one of these factors. The pH ofsoil affects the growth of plants in a number of ways. For example,growers can change the colour of hydrangea flowers by changing thesoil pH (Figure 5.14).

An important effect of altering soil pH is to change the availabilityof nutrients in the soil to plants. Plants can use only nutrients that aredissolved in the water in the soil. Different plant species requiredifferent levels of nutrients. In acidic soils, the nutrients phosphorus,potassium, calcium, and magnesium are less able to dissolve in the soilwater. A plant that needs high levels of these nutrients may not grow aswell in an acidic soil. Other nutrients, such as zinc, manganese, copper,and iron, dissolve more easily in acidic soil. A plant that needs highlevels of these nutrients may grow better in an acidic soil. The pH of thesoil therefore can determine if a plant gets too little or too much of anutrient.


• Neutralization is a type ofchemical reaction that occursbetween an acid and a baseand produces water and a salt.

• A precipitate is an insolublecompound that forms in somechemical reactions.

• Neutralization reactions can beused to help us solveenvironmental challenges.

Neutralization Reactions

Figure 5.13 Growers of fruits, vegetables, and other crops monitor and adjust the pH of soil inorder to provide the best growing conditions.

5.2

Figure 5.14 (a) When the soil pH is6.0 to 6.2, hydrangea flowers arepink. (b) When the soil pH is 5.2 to5.5, hydrangea flowers are blue.

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Adjusting Soil pHSoil pH can also change the variety and numbers of micro-organismsthat live in the soil. Some micro-organisms help plant growth, butothers cause disease.

Even areas that are close to each other can have different soilconditions, including soil pH. Therefore, farmers and other largegrowers, such as flower producers, need to know the soil pH in manyareas of their land. On commercial operations such as farms, soil pH isusually determined by specially trained technologists. On a smallerscale, home gardeners can test their soil using a test kit.

Once soil pH is known, growers can use this information in one oftwo ways. First, they could plant crops that are most suited to the soilpH. For example, legumes (beans and peas) grow best at a pH of 6.2 orhigher, but corn can do well in soils with a pH as low as 6.0. Second, agrower can adjust the pH of soil to support particular plants (Figure 5.15). If the soil pH is too acidic, adding a basic substance canincrease the pH. If the soil pH is too basic, then adding acidicsubstances can lower the pH.

B15 Quick Lab

Testing Soil pH

PurposeTo compare the pH of soil samples from differentsources

Procedure

1. Working on paper towels, remove any largerobjects, such as stones or twigs, from the pottingsoil. Break up any clumps with a teaspoon orscoopula.

2. Add soil to fill the testing container supplied withthe soil pH test kit, according to the instructionsthat came with the kit.

3. Add the testing powder to the soil in the testingcontainer. Add the amount of water indicated bythe manufacturer’s instructions.

4. Mix the contents. Allow any particles to settle,then compare the colour with the colour chartsupplied in the test kit.

5. Repeat steps 1 to 4 for the remaining soilsamples.


Questions

7. Potting soil is intended for use with a wide varietyof plants. Based on your analysis, do you thinkmost plants prefer acidic soil or basic soil?

8. Plants in the mint family grow best in basic soil(from pH 7.0 to 8.0). Which outdoor soil wouldbe best for mint?

9. Roses grow well in a pH range from 5.5 to 7.0.Which outdoor soil would be best for roses?

Figure 5.15 Calcium carbonate,commonly called lime, is added to soilto raise the pH.

• paper towels

• potting soil

• 2 or more samples ofsoil from outdoors

• teaspoon or scoopula

• soil pH test kit

• water


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During Reading NeutralizationNeutralization is a chemical reaction between an acid and a basethat produces water (H2O) and a salt (Figure 5.16). The salts formedmay be soluble in water or can be insoluble. If a salt is insoluble, aprecipitate will form. A precipitate is a suspension of small, solidparticles formed during a chemical reaction.

A neutralization reaction can be summarized as follows:

acid + base → salt + water

For example, the chemical equation for the neutralization reactionillustrated in Figure 5.16 is:

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)


Figure 5.16 When hydrochloric acid and sodium hydroxide are mixed in solution, theyundergo a neutralization reaction. The products are sodium chloride (table salt) and water.After the actual chemical reaction, the sodium chloride would be dissolved in the water.

Use Text ManagementStrategies

When good readers do not

understand, they may slow down

and reread parts of a text, read

ahead to get more clues from

words or graphics, or pause and

reflect, trying to connect what

they know to new knowledge.

Choose part of a text that you

found difficult, and try one of

these strategies to make meaning

of it.

Example Problem 5.1

When aqueous sulphuric acid reacts with solid sodium hydroxide,dissolved sodium sulphate and liquid water are produced. What is the balanced chemical equation for this neutralization reaction,including states?

1. Write a word equation for the reaction.sulphuric acid + sodium hydroxide → sodium sulphate + water

2. Write the correct formulas, using the charges on the periodictable. Include the states of matter.sulphuric acid: H2SO4(aq) sodium hydroxide: NaOH(s)sodium sulphate: Na2SO4(aq) water: H2O(l)

3. Write the skeleton equation. H2SO4(aq) + NaOH(s) → Na2SO4(aq) + H2O(l)

4. Write the balanced chemical equation, including states:H2SO4(aq) + 2NaOH(s) → Na2SO4(aq) + 2H2O(l)

Practice Problems

1. When HBr(aq) reacts withKOH(aq), a neutralizationreaction occurs. Theproducts are KBr(aq) and H2O(l). What is thebalanced chemical equationfor this reaction, includingstates?

2. When H2SO4(aq) reactswith Mg(OH)2(aq), theproducts are MgSO4(aq) and liquid water. Write thebalanced chemical equationfor this neutralizationreaction, including states.

3. When aqueous phosphoricacid reacts with aqueoussodium hydroxide, sodium phosphate(Na3PO4) and water areproduced. What is thebalanced chemical equationfor this neutralizationreaction, including states?

Reactants

HCI � �NaOH NaCI H2O

Products

+ +→

→

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Applications of Neutralization ReactionsNeutralization reactions have commercial uses, such as inpharmaceutical manufacturing, waste treatment, and agriculture. Inmaking pharmaceuticals, the pH of a solution may be changed fromacidic to basic (or vice versa) so that the desired product forms aprecipitate. The precipitate can then be collected by filtering theproducts of the reaction. In agriculture, calcium carbonate may beadded to acidic soil. The calcium carbonate enters into a neutralizationreaction with some of the acid in the soil water, and the soil pHbecomes more basic.

Neutralization reactions are also used in medicine. For example,acid reflux is a condition in which stomach acid (HCl) causesdiscomfort. The symptoms of acid reflux can be treated with antacids,which are composed of bases. They can produce a neutralizationreaction with some of the hydrochloric acid in the stomach. Bee stingscan also be treated using a neutralization reaction (Figure 5.17). Whenit stings, a bee releases methanoic acid, which attacks nerves in theskin. Bee stings can be treated with a cream that contains ammonia,which is a base. The ammonia enters into a neutralization reaction withthe methanoic acid, which prevents further irritation of the nerveendings.

The food industry uses neutralization reactions to adjust the pH ofproducts. Packaged and processed foods often have an acidic pH, sinceharmful bacteria are less likely to grow under these conditions. Forexample, vinegar (dilute acetic acid) or citric acid may be added to foodsto lower the pH. You will find vinegar in the ingredient list of manyprepared foods, such as ketchup (Figure 5.18).

You may be using acids and bases without realizing it. For example,we often serve fish with a wedge of lemon (Figure 5.19). Fish is a weakbase. Lemon juice (an acid) lowers the pH, which eliminates the fishyodour. Lemon juice is also often added to spinach salads. Spinachcontains iron, which is an important nutrient for your body. Lemonjuice contains vitamin C (ascorbic acid). Nutritionists believe thatadding lemon juice will help your body to absorb iron.


Figure 5.17 The methanoic acid in abee sting, also known as formic acid(HCOOH), can be neutralized with anammonia-based cream.

Figure 5.19 A neutralization reaction occurs whenlemon juice is added to fish.

Figure 5.18 Vinegar isadded to packaged foods,such as ketchup, for tasteand to prevent harmfulbacteria growing andcausing them to spoil.


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Using Neutralization Reactions to SolveEnvironmental ChallengesEvery day, you use products that use acids and bases in some way. Yourclothes may be dyed bright colours that are produced using acids andbases. Your home is made of materials such as lumber, steel, and copper,which are manufactured or processed using acids and bases. Althoughindustries that use acids and bases are beneficial to us, they can alsoaffect the environment negatively. Sometimes, neutralization reactionscan help to reduce negative effects and even repair environmentaldamage.

Acid PrecipitationAcid precipitation is rain, snow, fog, or dew that has a pH less than 5.6. (Rain usually has a pH of around 5.6.) Two main causesof acid precipitation are sulphur dioxide (SO2) and nitrogen oxides inthe atmosphere. Nitrogen oxides come in many forms, such as N2O,NO2, and N2O4. The gases then undergo chemical reactions in theatmosphere that result in the formation of acids, which eventually fallas acid precipitation.

Sulphur dioxide is converted to sulphuric acid by the following twochemical reactions:

2SO2(g) + O2(g) → 2SO3(g)SO3(g) + H2O(l) → H2SO4(aq)

Nitrogen dioxide gas dissolves in water droplets in the atmosphereto form nitric acid.

A significant source of gases that cause acid precipitation iselectricity production in coal-fired power plants. Iron and steelproduction, smelting of metals (such as zinc, nickel, and copper),fertilizer production, pulp and paper production, and automobileengines also emit gases that contribute to acid precipitation.

When acid precipitation falls on cities and towns, it can corrode thestone surfaces of buildings and statues and the concrete of roads andbridges. The acids in the precipitation enter into neutralizationreactions with bases in the stone. For example, limestone containscalcium carbonate, which can be dissolved by acid precipitation (Figure 5.20). Acids react with metals, so acid precipitation can causecorrosion of iron reinforcing rods in structures.

Acid precipitation changes the pH of the soil in forests, which cancause trees and other plant species to die (Figure 5.21(a)). This reduceshabitat for the species that depend on forests. Loss of forests meanslosses in the forestry industry and in recreational use. The water inlakes, streams, and other freshwater bodies can also become more acidicas a result of acid precipitation. The change in pH can cause fish andother water organisms to die (Figure 5.21(b)).

Figure 5.20 The damage to thelimestone on this building is the resultof acid precipitation.

Figure 5.21 (a) This photographshows the effect of acid precipitationon forests. (b) When lakes andstreams become too acidic, fish andother organisms may die.

(a)

(b)

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Neutralizing Acidic LakesIn some provinces, such as Alberta and Saskatchewan, most lakes arenaturally protected from the effects of acid precipitation because theyare surrounded by limestone. This type of rock reacts with excess acidand neutralizes it, which restores the pH of the lake water. However,this is not true of lakes in Ontario. The surroundings of Ontario lakesdo not contain much limestone, and a significant amount of acidprecipitation enters the lakes in Ontario. This means that Ontario lakesare at greater risk of acidification.

One way to raise the pH of heavily acidified lakes is by adding asubstance called lime. When lime mixes with water, the base calcium hydroxide (Ca(OH)2) is formed. Calcium hydroxide canneutralize both the sulphuric acid and the nitric acid that are found inacid precipitation. The neutralization reaction involving nitric acid is:

2HNO3(aq) + Ca(OH)2(s) → Ca(NO3)2(aq) + 2H2O(l)

However, this process is very expensive and,therefore, only practical in protecting lakeecosystems in the short term.

Reducing Acid PrecipitationOnce the relationship between sulphur dioxide andnitrogen oxides and acid precipitation wasunderstood, work began to develop technology thatcould help reduce the emission of these gases. Twoof those technologies are smokestack scrubbers andautomobile emissions controls.

Scrubbers are devices that are found in tallindustrial smokestacks of industries that releasesulphur dioxide gas and nitrogen oxide gases, suchas coal-fuelled power plants and ore smeltingfacilities (Figure 5.22). Scrubbers remove thesegases using a specially formulated chemicalmixture.


Figure 5.22 Scrubbers in these smokestacks trap pollutants thatcould otherwise cause acid precipitation.

Learning Checkpoint

1. What gases are the main causes of acid precipitaion?

2. What are nitrogen oxides?

3. Write two chemical equations for reactions that cause acid precipitation.

4. What is the source of water in the reactions you wrote in question 3?

5. Name two industries or human activities that contribute to acid precipitation.

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Figure 5.23 A catalytic converterconverts various emissions into lessharmful chemicals, often using acombination of metals and chemicalreactions.


The gases in a smokestack contact the chemical mixture in thescrubber and enter into chemical reactions. The products of thechemical reactions are a wet slurry or a solid. Scrubbers also have afilter that collects and traps small particles that would otherwise bereleased into the atmosphere. The substances collected can then beseparated and removed for recycling.

Internal combustion engines found in automobiles emit a number ofharmful gases, including nitrogen oxides. One approach to reducingharmful emissions is to use technologies that convert the harmful gasesto other, harmless substances. The most common of these technologiesis the catalytic converter, which is located in the exhaust system of avehicle (Figure 5.23). A catalytic converter uses nitrogen oxides in achemical reaction that decomposes them into nitrogen gas and oxygengas. For example, when dinitrogen trioxide is the reactant, the followingchemical reaction occurs:

2N2O3(g) → 2N2(g) + 3O2(g)

More Work NeededResearchers continue to closely study the acid content of lakes. Onestudy looked at changes in the pH of 152 lakes in southeastern Canada.From 1988 to 2008, only 41 percent of the lakes studied were lessacidic, 50 percent had not changed, and 9 percent were more acidic.

Central Ontario is the only region where there has been asignificant decline of acidity in most lakes. Scientists believe this changeis due mostly to the considerable reduction in sulphur dioxideemissions from smelters in the nearby Sudbury area. Computer modelshave predicted that up to one-quarter of the lakes in eastern Canadawill remain chemically damaged for years to come.

Learning Checkpoint

1. Describe two effects that acid precipitation has on the environment.

2. How can the pH of an acidic lake be increased?

3. Why are lakes on limestone rock less affected by acid rain?

4. What are scrubbers, and what do they do?

5. Catalytic converters use chemical reactions to reduce the emission of a

number of harmful gases. Write the chemical equation for the reaction with

dinitrogen trioxide that occurs in a catalytic converter.

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Heavy Metals Heavy metals are metal elements that have a high atomic mass.Examples of heavy metals include arsenic (As), copper (Cu), mercury(Hg), and zinc (Zn). Heavy metal accumulation can cause kidneydisease, diseases of the lungs, bone defects, and damage to nervoussystem development.

The soil in areas with a lot of heavy industry is often contaminatedwith heavy metals and other contaminants. However, roadways andautomobiles can also be contaminated with high levels of heavy metals(Figure 5.24). Copper may be released from bearings, engine parts, andbrakes, and nickel is found in diesel fuel and gasoline. Nickel andcadmium in rechargeable batteries can also cause heavy metalcontamination, if they are not properly disposed of.

Contamination at Mine SitesIn Ontario, many abandoned mine sites are significantly contaminatedwith heavy metals. Old mines often were operated in ways that wouldno longer be allowed. There were no rules that required mine owners toclean up the sites after the mines were closed.

In times past, waste from mines was stored in tailings ponds or inslag heaps. The rock waste (tailings) in these sites contained metals thatgenerate acids when they are exposed to air. For example, many minetailings in Ontario contain iron sulphide (pyrite or fool’s gold). In thepresence of oxygen and water, the iron sulphide enters into a series ofchemical reactions. The end products of these reactions are ironhydroxide, sodium sulphate, and sulphuric acid.

As this process continues, the soil and water in the area becomemore and more acidic. Acid leaching is a process in which acidsdissolve metals found in soil. As the pH falls, the heavy metals begin todissolve. At least 250 abandoned mine sites in Ontario continue to addto soil and water contamination through acid leaching of the wastes leftbehind (Figure 5.25). For example, the Kam Kotia mine site, locatednear Timmins, Ontario, caused acidification of soil and water andrelease of heavy metals into the surrounding areas.

Restoring SoilsSoils contaminated by heavy metals can be restored to a healthy state byacid leaching. When soil is heavily contaminated, such as in anabandoned mine, it is first removed and taken to a treatment facility.The contaminated soil is treated with acid to decrease the pH. Thisdissolves the metals in the soil, which are then collected in an acidicsolution. The metals are recovered by raising the pH of the solutionwith a base, which causes the metals to form a precipitate.

Neutralization reactions are used to prevent further acid leachingfrom mine sites. For example, at the closed Deloro Mine site nearPeterborough, Ontario, which was leaching heavy metals and the poison


Figure 5.24 Soils may becontaminated with heavy metalsanywhere that automobiles are used.

Figure 5.25 Tailings ponds and slagheaps at many abandoned mine sitesin Ontario are contaminating thesurrounding soil and water with heavymetals, through acid leaching.

The rehabilitation of theabandoned sites of the Kam Kotiamine, near Timmins, and of theDeloro mine, near Peterborough,continues. Find out what progresshas been made and whetherthese sites continue to negativelyaffect the environment. Begin yourresearch at ScienceSource.

Take It Further

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arsenic into the environment, an eight-hectare tailings pond was cappedwith half a metre of crushed limestone (calcium carbonate) to raise thepH and reduce the amount of acid leaching. Acid leaching at this oldgold mine had contaminated the water in the area with heavy metalsand the poison arsenic.


B16

Transporting Acids

On March 30, 2007, two dozen cars of an OntarioNorthland train jumped the tracks about 16 km north of Englehart, a community of about 1500 people northof North Bay, Ontario. Nine of the cars were carryingsulphuric acid. Over 100 tonnes (100 000 kg) of acidspilled into the Blanche River (Figure 5.26). Thismassive acid spill quickly killed fish and otherorganisms in or by the shores of the river. Healthofficials from Ontario’s Ministry of the Environment werealso concerned that the drinking water for the peopleand livestock in the area would be contaminated.

To monitor the damage caused by the acid spill,health officers immediately began to take water and soil samples at the spill site. To reduce theenvironmental impact, emergency response crewsadded kilogram amounts of lime (calcium hydroxide,Ca(OH)2) to the river several kilometres upstream.

1. Why was calcium hydroxide added to the river? Use a word equation and a skeleton equation inyour answer.

2. Should acids be transported large distances? Why or why not?


Figure 5.26 Sulphuric acid was released into the BlancheRiver when tank cars overturned, spilling their contents.

B17 Skill Builder Activity

In Activity B18, you will be making inferences. Aninference is a conclusion made by analyzing facts.When you draw conclusions about the observationsyou make in a scientific investigation, you are makinginferences. An inference is a logical analysis of facts,so it can always be justified by those facts.

For example, an advertisement states that 20 outof 25 people prefer Brand A cola over Brand B. Canyou infer that 80 percent of all people prefer Brand Acola? No, because you do not know how many peoplewere interviewed or how these people were chosen.Were they chosen at random, or were they all regularbuyers of Brand A cola? Without this information,there is not enough data to make an inference.

For each of the following situations, write an inferencebased on the given data. If there isn’t enough data tojustify an inference, write a sentence to explain why.

1. The juice stored in the back of the bottom shelf ofthe refrigerator is frozen. What can you infer aboutthe temperature in the refrigerator?

2. Your cake comes out of the oven looking more likea pancake than a light, fluffy cake. What can youinfer about the length of the baking time?

3. Eight in 10 dentists recommend Brand Xtoothpaste for reducing cavities. What can youinfer about this toothpaste?

Making an Inference

Suggested STSE Activity •B19 Inquiry Activity on page 214

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QuestionHow many drops of each antacid will you need toneutralize 5 drops of hydrochloric acid?

Procedure

1. Measure the pH of the HCl and of the threesamples of liquid antacid using pH paper. Recordyour data.

2. Using the dropper, add 5 drops of HCl to a well inthe spot plate.

3. Draw some of antacid A into a clean dropper. Addthree drops of antacid A to the HCl in the spotplate well (Figure 5.27). Mix the solution with aclean glass stirring rod.

4. Measure the pH of the solution with pH paper. Ifthe pH is close to 7, record the number of dropsof antacid A. If not, add another drop of theantacid and measure again. Continue until the solution is neutral or nearly neutral. Recordthe total number of drops of the antacid that you added.

5. Rinse the dropper.

6. Repeat steps 2 to 5 using antacid A again.

7. Repeat Steps 2 to 6 for antacid B and antacid C.



9. For each antacid, calculate and record the averagenumber of drops needed to neutralize the HCl.

10. Using your results, list the antacids in order frommost effective to least effective in neutralizing HCl.

11. Compare your results to others in your class. Whymight the results of all the groups not be the same?

Skill Practice

12. Identify the independent and dependent variablesin this investigation.

13. Why did you carry out two trials for each antacid?

Forming Conclusions

14. Based on your data, make an inference aboutwhich antacid would relieve acid indigestion mosteffectively. Give reasons for your answer.

Antacids and Neutralization Reactions

SKILLS YOU WILL USE■ Identifying variables■ Drawing conclusions

• 3 samples of liquid antacids (A, B, C)

• dilute hydrochloric acid (HCl)

• pH paper

• spot plate

• dropper

• glass stirring rod

Skills References 1, 2, 3


dropper

antacid

spot plate

HCl

Figure 5.27 Add drops of the antacid until the pH isclose to 7.

Key ActivityD

I

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The job of an environmental chemist includesconducting research and designing systems andequipment for measuring the quality of air, water, andsoil (Figure 5.28). Imagine you are an environmentalchemist studying the quality of water in lakes. Youhave just returned from a field trip with samples ofwater from several different lakes in northwesternOntario (Figure 5.29). This region has several old,abandoned mine sites that might be undergoing acidleaching of heavy metals. In this activity, you willdetermine the pH of lake water samples and then usea basic solution to neutralize them.

QuestionHow effective is a sodium hydrogen carbonate solutionin neutralizing acidic lake samples?

Procedure

1. In your notebook, make a table similar to Table5.8 (on the next page) to record your data.

2. Using a clean 10-mL graduated cylinder, measure5 mL of lake water sample A. Pour the 5 mL ofsample A into a clean 50-mL beaker.

Neutralizing Acidic Lake Water Samples

SKILLS YOU WILL USE■ Identifying variables■ Justifying conclusions

Skills References 2, 6

Figure 5.28 Environmentalchemists may collect watersamples as part of their work.

Hearst

Kapuskasing

Timmins

Chapleau

Wawa

ONTARIO

LakeSuperior

N

0 25 50 km

Figure 5.29 A map of the area of study, in which there are a number of old, abandonedmine sites

• lake water samples (labelled A, B, C, etc.)

• 10-mL graduated cylinders (1 per water sample)

• 50-mL beakers (1 per water sample)

• pH paper

• paper towels

• 0.1 M sodium hydrogen carbonate (NaHCO3(aq))solution

• stirring rod


STSE

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B19 Inquiry Activity (continued)

3. Measure the pH of sample A with pH paper.Record your data in your table.

4. Rinse the 10-mL graduated cylinder, and shake todry.

5. Use the clean 10-mL graduated cylinder tomeasure and add 1 mL of sodium hydrogencarbonate solution to the beaker. Stir the solutionwith the stirring rod.

6. Measure the pH of the solution in the beaker withpH paper.

7. If the pH of the solution in the beaker is still acidic, repeat steps 5 and 6 until the pH isapproximately 7. Keep track of the volume ofNaHCO3 solution you have added.

8. In your table, record the total volume of sodiumhydrogen carbonate solution you added to thesample to reach pH 7.

9. Rinse and dry the 10-mL graduated cylinder andthe 50-mL beaker.

10. Repeat steps 2 to 7 with the remaining lake watersamples.



12. Compare your results for the lake water samplesin your data table. How are they similar? How arethey different?

13. Compare your data with those of other groups inyour class. Suggest why your group’s results mayhave been different from the results of othergroups in your class.

Skill Practice

14. Why is it important to always start by measuringthe same volume (5 mL) of each of the watersamples?

Forming Conclusions

15. Would sodium hydrogen carbonate be suitable forneutralizing a lake? Support your decision withone or more reasons.

16. Suppose that one of the samples you tested wascollected from the site of an abandoned mine inthe area shown in Figure 5.29. Based on theinitial pH measurements you observed, which ofthe lake water samples would be most likely toindicate that heavy metal contamination of thewater might be occurring? Explain.

Acidic LakeWater Sample

Approximate pHof Sample

Volume ofNaHCO3 SolutionNeeded toNeutralize

Approximate pHof NeutralizedSample

Sample A

Sample B

Sample C

Table 5.8 Data Table for Lake Water Testing

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Key Concept Review1. Define “neutralization” in your own words.

2. What are the products of a neutralizationreaction?

3. How does an antacid work?

4. What is acid precipitation?

5. Name two gases that contribute to acidprecipitation.

6. Explain the term “acid leaching.” Use anexample in your answer.

Connect Your Understanding7. Identify which of the following is a

neutralization reaction. Explain how youknow.

(a) 2FeBr3 + 3Cu2SO4 → Fe2(SO4)3 + 6CuBr

(b) H3PO4 + 3NaOH → Na3PO4 + 3H2O

8. Complete the following word equations:

(a) sulphuric acid + calcium hydroxide →? + calcium sulphate

(b) hydrogen bromide + sodium hydroxide → water + ?

(c) ? + sodium hydroxide → water + sodium chloride

9. Write skeleton equations for each wordequation you completed in question 8.

10. Write balanced chemical equations for eachskeleton equation you wrote in question 9.

11. Suppose that a classmate combines acolourless acid and a colourless base. Theresulting solution is clear and colourless, withno evidence of a precipitate. Your classmatesays that this means that no reaction hasoccurred. Do you agree with your classmate’sconclusion? Explain.

12. You can temporarily receive relief from acidindigestion by using an antacid that contains abase. Why is it not a good idea to use anantacid routinely? Suggest two or morereasons.

13. Acids can react with most metals. Suggest whythis would be a problem in a region of Ontariowhere the rain is acidic.

14. Explain why acid precipitation is a costlyresult of human activities. Start your answerby referring to the photograph below.

15. Describe how acid precipitation affects lakes.

16. Explain what role limestone has in protectinglakes from acidification.

17. Describe the positive and negative effects ofacid leaching with respect to metal pollutionfrom disused mines.

Reflection18. What do you know about neutralization

reactions that you did not know before youstarted this section?




Question 14

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SCIENCEeverywhereeverywhere

Phosphoric acid (H3PO4) is an importantacid that is used in many ways. One way isto acidify foods and beverages, such as softdrinks. It gives foods a tangy or sour taste.

Phosphoric acid may beused for removing rustfrom iron or steel. It may beapplied as a liquid or as acomponent of a productcalled naval jelly. Thephosphoric acid in both theliquid or jelly convertsiron(III) oxide (rust) toiron(III) phosphate.

Etching solutions used in dentistry and orthodonticscontain phosphoric acid. Etching cleans and/orroughens the surfaces of teeth where dental appliancesor fillings are to be placed. The acid is applied for only ashort time and is quickly removed to prevent damage tothe enamel of the teeth. This process helps theappliance or filling to stick to the tooth more tightly.

Many fertilizers are made withphosphoric acid. Fertilizers arean important part of theagricultural industry. Care mustbe taken when choosing the typeand amount of a phosphatefertilizer. If too much phosphateis added to soil, it can dissolve inthe soil water and pollutewaterways.

Phosphoric Acid


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Key Concept Review1. List several properties of acids and bases.

Organize the list using a graphic organizersuch as a Venn diagram.

2. What is litmus paper? Describe the two typesof litmus paper.

3. What is the pH scale? What pH valuescorrespond to acidic, neutral, and basicsolutions?

4. Use the chemical or physical propertiesidentified below to classify each solution asacidic, basic, or neutral.

(a) reacts with magnesium to producebubbles and conducts electricity

(b) Blue litmus stays blue, and red litmus stays red.

(c) does not conduct electricity, and redlitmus stays red

(d) has a pH of 10, and blue litmus stays blue

(e) tastes bitter and does not react withmagnesium

Connect Your Understanding5. The pH of human blood is usually 7.35–7.45.

Is blood normally acidic, neutral, or basic?Explain how you know.

6. Suppose you have a colourless solution. Yoususpect it is an acid. How could you safelytest the liquid to confirm your suspicions?

7. How many times more acidic is a solution ofpH 3 compared to a solution of pH 5?

8. The person in the following photograph hasjust bitten into a sour lemon. Using what youknow about the properties of acids and bases,is the lemon acidic or basic?

9. From the following formulas, decide whetherthe compound is an acid, a base, or neither.

(a) H2SO4(aq)

(b) CH3COOH(aq)

(c) Mg(OH)2(aq)

10. Write the formula for each of the followingsubstances, and indicate whether each is anacid, a base, or neither.

(a) sulphuric acid

(b) calcium hydroxide

(c) hydrogen bromide solution

(d) magnesium hydroxide solution

11. Name each of the following, and indicatewhether it is an acid or a base.

(a) HF(aq)

(b) HNO3(aq)

(c) NaOH(aq)

(d) NH4OH(aq)

(e) CH3COOH(aq)

(f) H3PO4(aq)

(g) Ca(OH)2(aq)

a

a

a

a

a

t

a

k

k

k

k




tk

5 CHAPTER REVIEW

Question 8

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12. Fish will survive only in water that is withina specific, narrow pH range. Suggest at leasttwo ways that human activities could disruptthe normal pH of bodies of water and causeharm to fish.

13. Suppose that some hydrochloric acid is placedin a beaker and a pH meter is set into thesolution. It reads pH 1.5.

(a) Describe how the pH will change when asmall amount of NaOH solution is addeddrop by drop to the acid.

(b) Explain why the pH will change.

14. (a) Chemical reactions in your body producemore acids than bases. How might yourbody get rid of these extra acids?

(b) How could a lab technician test a urinesample to determine its pH?

15. Your saliva is usually basic.

(a) Suggest how basic saliva helps to protectyour health.

(b) Many soft drinks contain sugars, whichare converted to acids by bacteria in themouth. Based on your answer to (a),predict how drinking a lot of acidic softdrinks could affect your dental health.

16. Part of the job of an environmental chemist isto conduct research and design systems andequipment for measuring the quality of air,water, and soil. Suggest some positive aspectsof this science and technology career.

17. Use one of the acids or bases discussed in thischapter as a character in a story. Write yourstory in the first person. For example, yourstory might begin “I am hydrochloric acid,and this is my story.”

18. Choose an acid and a base from the lists inthis chapter. Suppose your acid and your baseare having a debate about whether acids orbases are more important and useful. Writethe dialogue for this debate, using facts aboutacids and bases from this chapter.

19. Figure 5.6 on page 197 illustrates a visual wayto remember the differences between acidsand bases. Design your own graphic to helpyou remember these differences.

20. Ontario produces some of its electricity fromcoal-fuelled power plants. The government ofOntario plans to shut these power plantsdown to reduce acid precipitation.

(a) How do coal-fired power plants contributeto acid precipitation?

(b) Describe a technology that can reduce theamount of acid precipitation caused bythe operation of a coal-fired power plant.

Reflection21. Describe at least three things about acids and

bases that you did not know before youcompleted this chapter.

22. What topics that were discussed in thischapter would you like to learn more about?Why? c

c

a

a

c

c

c

a

a

k

a

a

a

t

a


Reflect and Evaluate

Monitoring your understanding of text and having

ways to fix up meaning are important reading

strategies. List the During Reading strategies in this

chapter, and evaluate them. Which one was most

helpful to you? Rate the other ones from most helpful

to not very helpful. Compare your ratings with a

partner’s, and explain your reasons for the ratings.

After Reading

Unit Task Link

In the Unit Task, you will have an opportunity to

combine HCl(aq) and a piece of Mg ribbon. Do you

think that a neutralization reaction will occur

between these reactants? Explain your answer.

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6 Chemical reactions can be groupedaccording to the characteristics of theirreactants and products.

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Chemical reactions can be grouped according to the characteristics of their reactants and products. 221

The colourful patterns on these sails are the result of adye process that relies on chemical reactions.


• use appropriate terminology related to chemical reactions

• investigate simple chemical reactions, including synthesis,decomposition, and displacement reactions, and representthem using a variety of formats


• write word equations and balanced chemical equations forsimple chemical reactions

• describe, on the basis of observation, the reactants in andproducts of a variety of chemical reactions, includingsynthesis, decomposition, and displacement reactions

Why It Is ImportantThe products you buy and use every day are made usingchemical reactions. As a consumer, you have a responsibility touse these products safely and choose products that do the leastharm to the environment. Knowing about the types of chemicalreactions can help you do this. Many careers also require someknowledge of the types of chemical reactions.

Making Precise Observations

Scientists try to be very precise in describing what they see.

They use adjectives to describe the colour, shape, size,

quantity, and quality of substances and reactions. As you

read “The Chemistry of Steel,” note the adjectives that help

you to see and understand the substances and the process.

Key Terms

• combustion reaction • decomposition reaction

• displacement reaction • synthesis reaction

Before Writing

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The Chemistry of SteelSteel is the most widely used metal and most recycled material onEarth. Steel manufacturing is a major industry in Ontario, and steel hasbeen used in some of the most impressive architectural designs of ourtime, including the Art Gallery of Ontario (Figure 6.1). Steel is found inour homes, vehicles, appliances, tools, computers, and even in thezippers and clasps of our clothing. According to the Canadian SteelProducers Association, every Canadian owns an average of over 900 kgof steel!

Steel is made from highly purified iron and a small amount ofcarbon. The carbon in steel makes it much stronger than pure iron.Steel is produced from four materials: iron ore (mainly iron(III) oxide),coke, oxygen, and calcium carbonate (limestone). Coke is pure carbon,formed by heating coal in the absence of air.

The process of making steel begins in a smelter. A smelter containsa blast furnace, which is a chimney-like structure in which iron metal isextracted from iron ore in a process called “smelting” (Figure 6.2).During smelting, iron ore, coke, and limestone are loaded into the top ofthe blast furnace, while air is blown in from below. Smelting of the ironore produces an impure liquid metal called “hot metal.” When hotmetal solidifies, it is called “pig iron.”


• Chemical reactions can beclassified into types.

• You can identify the type ofchemical reaction byconsidering the reactants and products.

• In synthesis reactions, two or more elements combine to produce at least one new pure substance.

• In decomposition reactions, a single compound is brokendown into its elements.

Synthesis Reactions and Decomposition Reactions

Figure 6.1 The updated architecture of the Art Gallery of Ontario depends on the strength andmalleability of steel.

6.1

Figure 6.2 The extraction of ironmetal from iron ore is performed inthis enormous tower called a blastfurnace.

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223Chemical reactions can be grouped according to the characteristics of their reactants and products.

The first chemical reaction in the smelting process is betweencarbon (C) and oxygen (O2). The carbon monoxide (CO) that isproduced then reacts with the iron(III) oxide (Fe2O3) to give molteniron metal:

2C(s) + O2(g) → 2CO(g)

3CO(g) + Fe2O3(s) → 2Fe(l) + 3CO2(g)

Limestone (calcium carbonate, CaCO3) is then added to the hotmetal, Fe(l), to remove impurities and refine the iron. The initialchemical reaction breaks down the calcium carbonate, forming calciumoxide (CaO) and carbon dioxide (CO2). Next, the calcium oxide reactswith the impurities and produces molten calcium silicate (CaSiO3),commonly called slag.

CaCO3(s) → CaO(s) + CO2(g)

CaO(s) + SiO2(s) → CaSiO3(l)

Calcium silicate is less dense than molten iron, so it can be pouredoff separately, leaving behind the purified iron. Iron is converted to steelby adding small amounts of carbon and, in some cases, elements such asmanganese, silicon, nickel, molybdenum, and chromium (Figure 6.3).This process produces the steel that you use and employs thousands ofCanadians.

B20 Quick Lab

Simulating Chemical Reactions

Figure 6.3 Stainless steel containsiron, carbon, and at least 11 percentchromium.

B ABA

Figure 6.4 The two tennis balls can interact by forming a pair.

B AB A

Figure 6.5 Here, the two tennis balls can interact by coming apart.

PurposeTo use tennis balls to model chemical reactions

Procedure

1. Suppose you have two tennis balls, A and B, thatare apart. One way that they can interact is to join(Figure 6.4), forming the pair AB. If balls A and Bwere already joined, the only interaction would befor them to separate (Figure 6.5).

Questions

2. What kinds of interactions are possible amongthree tennis balls? Draw, label, and colour thepossible interactions for three tennis balls, A, B,and C.

3. Repeat the exercise using four tennis balls, A, B,C, and D.

4. Share the interactions you find with one or moreof your classmates.

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Types of Chemical ReactionsThere are many possible ways that elements and compounds mayinteract. In other words, there are many types of chemical reactions.When you can identify a reaction type from the reactants, you canpredict the products of the reaction. Predicting products is important inthe manufacture of many of the consumer goods we use, such asplastics (Figure 6.6). When chemists develop new plastics, they predictthe products of the chemical reactions they use.

Each type of chemical reaction can be represented by a generalchemical equation. A general chemical equation (GCE) is an equationthat uses letters of the alphabet (A, B, C, D) in place of the symbols forelements. A GCE can help you understand and remember a type ofchemical reaction more easily. Table 6.1 shows how letters are usedwhen writing a GCE.


Figure 6.6 New plastics aredeveloped using chemical reactionsthat are predicted to give productswith different properties.

Symbol or Formula Meaning

a single letter (e.g., A, B, X)

a metallic element (e.g., Li or Mg) or a non-metallicelement (e.g., H or F)

H hydrogen ion (in an acid), on the left of the formula (e.g., HCl)

OH hydroxide ion (in a base), on the right of the formula (e.g., NaOH)

AB or CD an ionic compound with a metallic ion and a non-metallicion, such as Li2O or MgBr2

AB or CD a molecular compound of two non-metals, such as H2O or CO

H2O water (compound)

CO2 carbon dioxide (compound)

Table 6.1 Symbols and Formulas Used in General Chemical Equations

For example, in chapter 5, you explored neutralization reactionsbetween acids and bases. The GCE for a neutralization reaction is:

General chemical equation: HB +XOH → XB + H2O

Word equation: sulphuric acid + sodium hydroxide → sodium sulphate + water

Skeleton equation: H2SO4(aq) + NaOH(s) → Na2SO4(aq) + H2O(l)

Balanced chemical equation: H2SO4(aq) + 2NaOH(s) → Na2SO4(aq) + 2H2O(l)

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Synthesis Reactions In the simplest type of synthesis reaction, two elements combine to form a compound. Either a metallic element combines with a non-metallic element or a non-metallic element combines with a second non-metallic element to produce one compound. A generalstatement for a synthesis reaction is:

element + element → compound

The general chemical equation for a synthesis reaction is:

A + B → AB

Whenever the reactants of a chemical reaction are two elements andthe product is a single compound, you know that the chemical reactionis a synthesis reaction. For example, when the metallic elementmagnesium burns in the presence of oxygen gas, magnesium oxide isformed (Figure 6.7). Oxygen is a non-metallic element that formsdiatomic molecules. The formulas and states of matter at roomtemperature of some common molecular elements and compounds areshown in Table 6.2.

Skeleton equation: Mg(s) + O2(g) → MgO(s)

Balanced chemical equation: 2Mg(s) + O2(g) → 2MgO(s)

Magnesium oxide has a number of commercial uses, includingmaking reflective coatings for optical instruments and lining metal andglass furnaces.

Sulphur and oxygen can also undergo a synthesis reaction,producing a poisonous gas called sulphur dioxide. In this case, bothreactants are non-metallic elements.

Skeleton equation: S8(g) + O2(g) → SO2(g)

Balanced chemical equation: S8(g) + 8O2(g) → 8SO2(g)

As you saw in chapter 5, sulphur dioxide can combine with waterin the air to form acid rain. That is why as much sulphur as possible isremoved from gasoline during production.

Another synthesis reaction involving only non-metals is thesynthesis of ammonia from its elements. The formula of ammonia isNH3, so the reactants must be the elements hydrogen and nitrogen.Both of these elements form diatomic molecules.

Skeleton equation: H2(g) + N2(g) → NH3(g)

Balanced chemical equation: 3H2(g) + N2(g) → 2NH3(g)

Since ammonia is used in the production of fertilizers and otheruseful compounds, synthesizing ammonia is an important industrialreaction.


Figure 6.7 Magnesium oxide is theashy, white solid below the flame.

WORDS MATTER

The word “synthesis” comes from two Greek words: syn meaning“together” and tithenai, meaning“put.” Synthesis therefore literallymeans put together.

Table 6.2 Common MolecularElements and Compounds,with States at RoomTemperature

Formula (State) Name

Molecular Elements

H2(g) hydrogen

N2(g) nitrogen

O2(g) oxygen

F2(g) fluorine

Cl2(g) chlorine

Br2(l) bromine

I2(s) iodine

P4(s) phosphorus

S8(s) sulphur

Molecular Compounds

CH4(g) methane

H2O(l) water

NH3(g) ammonia

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Example Problem 6.1

Sodium sulphide is a yellow-red solid that is used in making dyesand in processing wood pulp. Although sodium sulphide is notproduced commercially this way, a chemical reaction between solidsodium and solid sulphur will produce solid sodium sulphide.Identify the type of chemical reaction, and then write the balancedchemical equation, including states.

1. Write the word equation for the reaction. sodium + sulphur → sodium sulphide

2. Identify the type of chemical reaction from the nature of thereactants and products.

• Sodium is a metallic element, sulphur is a non-metallicelement, and sodium sulphide is a compound. Therefore,the chemical reaction is a synthesis reaction.

3. Use the word equation to write the skeleton equation,including states.

• Sulphur is a molecular element with the formula S8. Thisinformation must be read from a chart or memorized. Na(s) + S8(s) → Na2S(s)

4. Write the balanced chemical equation for the reaction.16Na(s) + S8(s) → 8Na2S(s)

Practice Problems

1. Lithium and chlorinecombine to produce lithiumchloride. Identify the typeof chemical reaction, andthen write the balancedchemical equation.

2. Calcium oxide is producedfrom calcium and oxygen.Identify the type ofchemical reaction, and thenwrite the balanced chemicalequation.

3. Carbon dioxide gas can be formed from two non-metals, solid carbon and oxygen gas. Identify the type of chemicalreaction, and then write the balanced chemicalequation, including states.

Decomposition Reactions During a decomposition reaction, a compound is broken apart intotwo or more elements and/or simpler compounds. A decompositionreaction is the reverse of a synthesis reaction. The elements that areproduced may be a metallic element and a non-metallic element or twonon-metallic elements.

compound → element + element

The GCE for a decomposition reaction is:

AB → A + B

Whenever the reactant of a chemical reaction is a single compoundand the products are elements or simpler compounds, you can identifythe chemical reaction as a decomposition reaction.

For example, chemists in the 18th century prepared oxygen gas byheating solid mercury(II) oxide, leaving globules of mercury metal.

Skeleton equation: HgO(s) → Hg(l) + O2(g)

Balanced chemical equation: 2HgO(s) → 2Hg(l) + O2(g)


Synthesis and decompositionreactions are more common andimportant than you might think.Prepare a script for a shortnewscast or documentary on oneor both of these types of chemicalreactions using information andimages. Begin your research atScienceSource.

Take It Further

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The breakdown of water into hydrogen and oxygen is anotherexample of a decomposition reaction. Figure 6.8 shows anapparatus that is used to decompose water in a laboratory. Thisapparatus is called the Hoffman apparatus, and it decomposeswater by passing electricity through it.

Skeleton equation: H2O(l) → H2(g) + O2(g)

Balanced chemical equation: 2H2O(l) → 2H2(g) + O2(g)

Some vehicles now use hydrogen gas as fuel for at least part oftheir energy needs. However, it is not practical to use electricity toproduce the amounts of hydrogen gas needed by hydrogen-fuelledvehicles.

Large volumes of hydrogen are produced by the decompositionof methane (CH4, natural gas). A device called a reformer or a fuelprocessor splits the hydrogen atoms from the carbon atoms in themethane. This method of producing hydrogen gas has two maindisadvantages. First, it depends on methane gas, which is a non-renewable energy source. Secondly, it also produces carbondioxide, a greenhouse gas that contributes to global warming.


Example Problem 6.2

Solid calcium chloride is used to reduce dust on roads and inmines. When calcium chloride is heated to a sufficiently hightemperature, it undergoes a chemical reaction that producessolid calcium and chlorine gas. Identify the type of chemicalreaction, and then write the balanced chemical equation,including states.

1. Write the word equation for the reaction. calcium chloride → calcium + chlorine

2. Identify the type of chemical reaction from the nature ofthe reactants and products.

• Calcium chloride is a compound, and calcium andchlorine are elements. Therefore, this is a decomposition reaction.

3. Use the word equation to write the skeleton equation.CaCl2(s) → Ca(s) + Cl2(g)

4. Write the balanced chemical equation for the reaction.CaCl2(s) → Ca(s) + Cl2(g)

Practice Problems

1. During a chemical reaction,magnesium and sulphur areproduced from magnesiumsulphide. Identify the typeof chemical reaction, andthen write the balancedchemical equation.

2. When heated, sodium iodidemay be broken down intosodium and iodine. Identifythe type of chemicalreaction, and then write thebalanced chemical equation.

3. Chlorine gas is used todisinfect water in drinkingsupplies and pools, and inmaking plastics,pharmaceuticals, andfertilizers. In the lab,chlorine gas and sodiummetal can be produced bypassing an electric currentthrough hot, molten sodiumchloride, which is a liquid.Identify the type of chemicalreaction, and then write thebalanced chemical equation,including states.

water added here

escaping gascollected here

hydrogen H2(g)

oxygen O2(g)

Figure 6.8 A Hoffman apparatus breakswater down into oxygen and hydrogen usingelectricity. This process is called electrolysis.

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QuestionWhat changes will you observe during a synthesisreaction between iron and oxygen-rich air?

Procedure

1. Light the Bunsen burner with matches or a flint striker.

2. Using long tweezers or tongs, pick up a piece ofsteel wool. Hold the steel wool in the flame until itbegins to burn.

3. Remove the steel wool from the flame, and allow itto finish burning. Observe the burnt steel wool.Record your observations.

4. Using a 25-mL graduated cylinder, measure 20 mL of 3% hydrogen peroxide solution. Pourthis hydrogen peroxide into the 125-mLErlenmeyer flask.

5. Using a clean scoopula, measure a pea-sizedamount (about 1 mL) of potassium iodide powderinto the Erlenmeyer flask.

6. Gently swirl the contents of the flask for a fewseconds. Observe the formation of bubbles. Theseare bubbles of pure O2(g).

7. Using the tweezers or tongs, pick up the secondpiece of steel wool. Hold the steel wool in theflame until it begins to burn.

8. Plunge the burning steel wool into the Erlenmeyerflask (Figure 6.9).

9. Put out the Bunsen burner, and then record yourobservations of the steel wool.



11. Describe the differences between burning steelwool (a source of iron) in air and burning it in airthat is rich in oxygen (from hydrogen peroxide).

12. Rewrite the following sentence as a balancedchemical equation (include the state symbols):“Solid iron reacts with oxygen gas to form solidiron(III) oxide.”

Skill Practice

13. In point form, outline all the safety precautionsthat you used while you conducted this lab.

Forming Conclusions

14. Describe the observations you made that providedevidence that a chemical reaction had occurred.

Synthesis of Iron(III) Oxide

SKILLS YOU WILL USE■ Using equipment, materials, and

technology accurately and safely■ Interpreting data/information to

identify patterns or relationships

CAUTION: Tie back long hair and fasten any looseclothing.

• Bunsen burner

• matches or flint striker

• long tweezers or tongs

• 2 pieces of steel wool


• scoopula

• paper towels

• potassium iodide (KI) powder

• 125-mL Erlenmeyerflask

• 3% hydrogen peroxide solution(H2O2(aq))




burningsteel woolhydrogenperoxide

Erlenmeyerflask

tweezers

Figure 6.9 The burning steel wool does not need to contact theliquid in the Erlenmeyer flask. Do not get the steel wool wet.

Key ActivityDI

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Key Concept Review1. Name the two types of chemical reactions

discussed in this section.

2. You learned about neutralization reactions inchapter 5 and reviewed them in this section.What are the products of a neutralizationreaction?

3. Write the general chemical equation for eachof the following types of chemical reactions.

(a) a synthesis chemical reaction

(b) a decomposition chemical reaction

(c) a neutralization reaction

4. Classify each of the following chemicalreactions.

(a) CaCl2(s) → Ca(s) + Cl2(g)

(b) NaN2(s) → Na(s) + N2(g)

(c) 2Rb(s) + Cl2(g) → 2RbCl(s)

(d) 4Li(s) + O2(g) → 2Li2O(s)

(e) 2NaCl(s) → 2Na(s) + Cl2(s)

(f) 2NI3(aq) → N2(g) + 3I2(s)

Connect Your Understanding5. (a) Identify the following chemical reaction

as either a synthesis or a decomposition.Explain how you know.

2Fe(s) + O2(g) → 2FeO(s)

(b) In the chemical reaction in (a), which ofthe possible ions of iron is in thecompound FeO(s)? (Hint: Use theperiodic table to check.)

(c) Explain how you answered 5(b).

6. If you heat solid potassium chlorate (KClO3),it decomposes into solid potassium chlorideand oxygen gas. For the decomposition ofpotassium chlorate, write:

(a) the word equation

(b) the skeleton equation, including states

(c) the balanced chemical equation, including states

7. Water can be decomposed by passing a large electrical current through it. Write the balanced chemical equation for thedecomposition reaction for water. Include states.

8. Zinc nitride is a solid chemical used inelectronics. Write the balanced chemicalequation for the synthesis of solid zinc nitridefrom solid zinc and nitrogen gas. Start withthe word equation. Follow the steps shownearlier in this chapter, including states.

9. Magnesium chloride powder is sprinkled onroads and sidewalks to reduce ice formation.Write the word equation, skeleton equation,and balanced chemical equation, includingstates, for the synthesis of solid magnesiumchloride from solid magnesium metal andchlorine gas.

10. Iron and oxygen can combine to produceiron(III) oxide (rust), as shown in thephotograph below. Explain why knowledge of this synthesis reaction is important in daily life.

Reflection11. Using a poster, a Web page, or another

creative method of your choosing, describe atleast two things that you found to be the mostinteresting in this section.




Question 10

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The Hottest FlameWhen we need two pieces of metal to be joined together, a common wayof doing so is to weld them. Welding involves melting the edges of thepieces to be joined, which then form a seam when they cool. Meltingmetal requires high temperatures. During welding, only specific parts ofa metal piece must be melted and not the whole piece. One way ofgetting such precise melting is to use an oxyacetylene torch (Figure 6.10).

Oxyacetylene torches work by burning acetylene gas. The balancedchemical equation for this reaction is:

2C2H2 + 5O2 → 4CO2 + 2H2O

An oxyacetylene torch contains a cylinder of acetylene and acylinder of oxygen. In this type of torch, the acetylene burns in a streamof pure oxygen gas. The flame of an oxyacetylene torch has atemperature of about 3000°C. When acetylene burns in air, the flamewill reach a maximum temperature of only about 538°C. Burning theacetylene in pure oxygen enables the flame temperature to become hotenough to melt steel.

As well as producing heat for welding, acetylene gas is used in thesynthesis of many other products. However, its usefulness wasrecognized only when an experiment failed. Thomas L. Willson was the first to make acetylene and to find ways to use it (Figure 6.11).


• In combustion chemicalreactions, an element or acompound reacts rapidly withoxygen.

• In single displacementreactions, a reactive elementreacts with a compound.

• Double displacement reactionsoccur between two ioniccompounds.

Combustion Reactions and DisplacementReactions

Figure 6.10 An oxyacetylene torch burns acetylene gas in a stream of oxygen gas, producing aflame that is hot enough to melt metal.

6.2

Figure 6.11 Thomas L. Willson wasborn in Princeton, Ontario, in 1860.He accidentally found a way toproduce acetylene gas.

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He was trying to produce aluminum metal by reacting aluminumoxide with carbon. The reaction produced only a few small globules ofaluminum. Willson next tried reacting calcium oxide with carbon toproduce calcium. This time, a solid formed.

When solid calcium reacts with water, aqueous calcium hydroxideand hydrogen gas are produced. Therefore, to see if the solid that hadformed was calcium, Willson mixed it with water. A gas was produced.Willson next tested to see if the gas was, in fact, hydrogen. To hissurprise, it was not. Instead, the solid product was calcium carbide,CaC2, and the gas product was acetylene, C2H2. The initial reaction hadbeen:

calcium oxide + carbon → calcium carbide + carbon monoxideCaO(s) + 3C(g) → CaC2(s) + CO(g)

The calcium carbide had then reacted with water as follows:

calcium carbide + water → calcium hydroxide + acetyleneCaC2(s) + 2H2O(l) → Ca(OH)2(aq) + C2H2(g)

B22 Quick Lab

Observing Reactions in Solution

PurposeTo combine solutions of ionic compounds andobserve what happens

Procedure

1. Fill three test tubes about 2 cm with sodiumhydroxide solution. Place them in the test-tuberack.

2. Fill one of the remaining test tubes to a depth ofabout 2 cm with iron(III) chloride solution.

3. Repeat step 2 with copper(II) chloride solutionand nickel(II) nitrate solution.

4. Into each of the test tubes from steps 2 and 3,pour the sodium hydroxide solution from one ofthe test tubes from step 1. Observe.

5. Without spilling or allowing the liquid to touchyour skin, shake each test tube to promotemixing. Observe.

6. Using a stirring rod, remove some of the solidthat has formed in each test tube and examine it.


Questions

8. What evidence was there that chemical reactionsoccurred with each mixing?

9. Each reaction had two reactants and twoproducts. By looking at the names of eachreactant, you may be able to predict the names of each product. (Hint: one of the products issodium chloride.)

10. Write a word equation and balanced formulaequation for each reaction.

• 6 medium test tubes

• sodium hydroxidesolution

• test-tube rack

• iron(III) chloridesolution

• copper(II) chloridesolution

• nickel(II) nitratesolution

• paper towel

• stirring rod


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Combustion Reactions of Hydrocarbons A combustion reaction is a chemical reaction in which a compound orelement rapidly combines with oxygen gas. These reactions usually giveoff a large amount of heat and light. A hydrocarbon is a compoundmade of only carbon and hydrogen. Hydrocarbons have the formulaCxHy where the letters “x” and “y” stand for the number of atoms (i.e., 2, 3, or higher). The simplest example of this kind of compound ismethane (CH4) (Figure 6.12). Some of these compounds are fossil fuels,such as methane and petroleum. Fossil fuels are hydrocarbons formedunderground over millions of years from the remains of once-livingorganisms. The general chemical equation for the combustion reactionof a hydrocarbon is:

CxHy + O2 → CO2 + H2O

(where CxHy stands for a hydrocarbon molecule).

We write CxHy in the general chemical equation because there aremany different compounds made up of only carbon and hydrogenatoms. The products of a hydrocarbon combustion reaction are alwayscarbon dioxide and water.

For example, the combustion reaction of methane gas can be writtenthis way:

Impact on the EnvironmentWhen combustion reactions of hydrocarbons release carbon dioxide gasinto the atmosphere, they play a role in global warming. Atmosphericcarbon dioxide gas prevents thermal energy from escaping into space. Asthe levels of carbon dioxide gas have increased over the last century, theaverage temperature on Earth has also increased.

Combustion reactions can be used to help the environment. Whenoil is spilled on land, the oil spill may first be set on fire. Thecontaminated soil is then removed for additional treatment. Thecombustion of an oil spill can produce toxic smoke, and so this methodis unlikely to be used on a spill near human populations. Combustionmay also be used to clean up oil spills on water (Figure 6.13).

More commonly, oil spills on water are absorbed by enclosing the oil slick with large, floating sponges. The sponges are then collected and treated elsewhere. When an oil spill has reached the shore, micro-organisms may be used in the clean-up efforts. Fertilizers, such asphosphorus and nitrogen, are spread over the affected area of theshoreline. The fertilizers promote the growth of the micro-organisms,which break down the oil into harmless or less-toxic substances.


Figure 6.12 The combustion ofmethane (natural gas) is commonlyused to produce heat for cooking andfor heating.

Skeleton equation: CH4(g) + O2(g) → CO2(g) + H2O(l)

Balanced chemical equation: CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)

Figure 6.13 Intentionally burning offspilled oil on water is still mainlyexperimental. Combustion of spilledoil is mainly used for oil spills on land.

WORDS MATTER

The word “combustion” comes fromthe Latin word comburere whichmeans to burn up.

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Single Displacement ReactionsIn a single displacement reaction, an element reacts with an ioniccompound. During the reaction, the element becomespart of the ionic compound, while one of the elements in the ioniccompound becomes an element by itself. The elements that switchplaces may be either two metals or two non-metals.

In the first type of displacement reaction, a metallic atom tradesplaces with a metallic ion in a compound. The general chemicalequation for this single displacement reaction is:

AB + C → CB + A

(where the metallic element A is replaced by another metal, C).

In this type of single displacement reaction, the reactants willalways be a compound and a metallic element, and the products alsowill always be a compound and a metallic element.

For example, a single displacement reaction can take place betweencopper(II) chloride and aluminum. This reaction is written as:


Example Problem 6.3

When solid magnesium reacts with aqueous silver nitrate, silverand aqueous magnesium nitrate are produced. Identify the type ofchemical reaction, and then write a balanced chemical equation forthe reaction, including states.

1. Write the word equation for the reaction.silver nitrate + magnesium → magnesium nitrate + silver


• Magnesium and silver are metallic elements. Silver nitrateand magnesium nitrate are compounds. Therefore, this is asingle displacement reaction.

3. Use the word equation to write the skeleton equation,including states.AgNO3(aq) + Mg(s) → Mg(NO3)2(aq) + Ag(s)

4. Write the balanced chemical equation.2AgNO3(aq) + Mg(s) → Mg(NO3)2(aq) + 2Ag(s)

Practice Problems

1. When magnesium metaland zinc nitrate react, theyform zinc and magnesiumnitrate. Identify the type ofchemical reaction, and thenwrite a balanced chemicalequation for the reaction.

2. Iron metal is placed into asolution of silver nitrateand allowed to sit. Thisproduces aqueous iron(II)nitrate and solid silvermetal. Identify the type ofchemical reaction, and thenwrite a balanced chemicalequation for the reaction,including states.

Skeleton equation: CuCl2(aq) + Al(s) → AlCl2(aq) + Cu(s)

Balanced chemical equation: 3CuCl2(aq) + 2Al(s) → 2AlCl2(aq) + 3Cu(s)

Suggested Activity •B25 Design a Lab on page 239

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In the second kind of displacement reaction, a non-metal in acompound is displaced by another non-metal. The general chemicalequation for this single displacement reaction is:

AB + C → AC + B

(where the non-metallic element B is replaced by another non-metal, C).

In this form of single displacement reaction, the reactants willalways be a compound and a non-metallic element, and the productswill also always be a compound and a non-metallic element.

For example, a single displacement reaction can take place betweenpotassium iodide and bromine. This reaction is written as:


Skeleton equation: KI(aq) + Br2(l) → KBr(aq) + I2(aq)

Balanced chemical equation: 2KI(aq) + Br2(l) → 2KBr(aq) + I2(aq)

Example Problem 6.4

When they are both in an aqueous solution, chlorine gas andcalcium bromide react to produce bromine liquid and aqueouscalcium chloride. Identify the type of chemical reaction, and thenwrite a balanced chemical equation for the reaction, includingstates.

1. Write the word equation for the reaction.chlorine + calcium bromide → bromine + calcium chloride


• Chlorine and bromine are non-metallic elements. Calciumbromide and calcium chloride are compounds. Therefore,this is a single displacement reaction. Both chlorine andbromine are diatomic in their pure element form.

3. Use the word equation to write the skeleton equation,including states. CaBr2(aq) + Cl2(aq) → CaCl2(aq) + Br2(l)

4. Write the balanced chemical equation for the reaction.CaBr2(aq) + Cl2(aq) → CaCl2(aq) + Br2(l)


Practice Problems

1. Fluorine and aluminumbromide undergo a chemicalreaction to produce bromineand aluminum fluoride.Identify the type ofchemical reaction, and thenwrite a balanced chemicalequation.

2. Bromine and silver chlorideare produced whenchlorine and silver bromideundergo a chemicalreaction. Identify the typeof chemical reaction, andthen write a balancedchemical equation.

3. Chlorine gas reacts with asolution of aqueousnickel(III) bromide andproduces aqueousnickel(III) chloride andliquid bromine. Identify thetype of chemical reaction,and then write a balancedchemical equation for thereaction, including states.

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The combustion of hydrocarbonsprovides energy for many humanactivities. Prepare a poster oranother form of display for yourclassroom using information andimages. Begin your research atScienceSource.

Take It FurtherDouble Displacement Reactions In a double displacement reaction, the positive or negative ions intwo dissolved ionic compounds switch places. The general chemicalequation for a double displacement reaction is:

AB + CD → AD + CB

In a double displacement reaction, the reactants will always becompounds. Therefore, a positive ion will only switch places with apositive ion, and a negative ion will only switch places with a negativeion. Two positive ions will never pair up to form a new compound,because their charges will repel one another. Two negative ions willnever pair up to form a new compound for the same reason. Doubledisplacement reactions may result in the formation of a precipitate.

For example, when aqueous magnesium hydroxide combines withaqueous silver nitrate, the products are aqueous magnesium nitrate andsilver hydroxide.


Skeleton equation: Mg(OH)2(aq) + AgNO3(aq) → Mg(NO3)2(aq) + AgOH(s)

Balanced chemical equation: Mg(OH)2(aq) + 2AgNO3(aq) → Mg(NO3)2(aq) + 2AgOH(s)

You are not expected to be able to predict the states of the productsin a double displacement reaction.

Example Problem 6.5

When aqueous lead(II) nitrate and aqueous sodium iodide aremixed, solid lead(II) iodide and aqueous sodium nitrate areformed. Identify the type of chemical reaction, and then write abalanced chemical equation for the reaction.

1. Write the word equation for the reaction.

lead(II) nitrate + sodium iodide → lead(II) iodide + sodium nitrate


• The reactants and products are all ionic compounds.Therefore, this is a double displacement reaction.

3. Use the word equation to write the skeleton equation,including states. Pb(NO3)2(aq) + NaI(aq) → PbI2(s) + NaNO3(aq)

4. Write the balanced chemical equation for the reaction.Pb(NO3)2(aq) + 2NaI(aq) → PbI2(s) + 2NaNO3(aq)

Practice Problems

1. When aqueous aluminumchloride and aqueoussodium hydroxide react,solid aluminum hydroxideand aqueous sodiumchloride form. Identify thetype of chemical reaction,and then write a balancedchemical equation,including states.

2. When aqueous copper(I)nitrate and aqueouspotassium bromide react,solid copper(I) bromideand aqueous potassiumnitrate are produced.Identify the type ofchemical reaction, andthen write a balancedchemical equation,including states.

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Neutralization and Double DisplacementA neutralization reaction between an acid and a base also follows thesame general pattern as a double-displacement reaction. Recall that in aneutralization reaction, an acid reacts with a base to form an ionic saltand water. The general chemical equation for this reaction is:

HB + XOH → XB + H2O

(where HB is an acid, XOH is a base, and XB is an ionic salt).

Another way of looking at this reaction is that the H+ion in theacid switches places with the positive ion (X) in the base, or the OH� ion in the base switches places with the negative ion (B) in theacid. Since neutralization reactions are so common and so important,they are classified on their own and are not usually called doubledisplacement reactions.

Summary: Types of Chemical ReactionsTable 6.3 summarizes the types of chemical reactions you explored inthis chapter and in chapter 5. The general chemical equation and anexample of a matching balanced chemical equation are shown for each.


During Writing

Type of Chemical ReactionType of Reactant(s) (R) andProduct(s) (P)

General Chemical Equation(GCE)

Balanced Chemical Equationof Example Reactions

Synthesis R: two elements P: a single compound

A + B → AB 2Mg(s) + O2(g) →2MgO(s)

Decomposition R: a single compoundP: elements and/or simplercompounds

AB → A + B CaCl2(s) → Ca(s) + Cl2(g)

Combustion of hydrocarbons R: a hydrocarbon and oxygenP: carbon dioxide and water

CxHy + O2 → CO 2 + H2O CH4(g) + 2O2(g) →CO2(g) + 2H2O(l)

Single displacement R: a compound and a metalelementP: a compound and a metalelementORR: a compound and a non-metal elementP: a compound and a non-metal element

AB + C → CB + A

DB + C → DC + B

2FeCl3(aq) + 3Mg(s) →3MgCl2(aq) + 2Fe(s)

2KI(aq) + Br2(l) →2KBr(aq) + I2(aq)

Double displacement R: two aqueous ioniccompoundsP: two ionic compounds

AB + CD → AD + CB Ca(OH)2(aq) + 2AgNO3(aq) →Ca(NO3)2(aq) + 2AgOH(s)

Neutralization R: an acid and a baseP: a salt and water

HB + XOH → XB + H2O H2SO4(aq) + 2NaOH(s) →Na2SO4(aq) + 2H2O(l)

Table 6.3 Summary Chart for Types of Chemical Reactions

Keep Your Emotions in Check

Scientists try to be objective rather

than emotional. They base their

arguments on research — their

conclusions are drawn from

observations and experiments. As

you prepare arguments for a

debate, remember to keep

emotions in check and to base your

points on scientific research.

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B23

A New Fertilizer Plant: Beneficial or Harmful?

A fertilizer manufacturing company would like to builda large factory in your community. The factory wouldbring jobs and more tax revenue to the community.However, chemicals will need to be transported inand out of the factory. The plant will also use a lot ofwater, electricity, and other energy sources, such ashydrocarbons (for combustion reactions).

1. Your teacher will place you in a group thatrepresents one of the following stakeholders:

• an investor in the fertilizer plant• an unemployed worker• a city government official• a homeowner in the area of the proposed

plant• an environmentalist

2. In your group, decide if you will support theconstruction of the proposed fertilizer factory.Consider positive and negative effects. If youneed to do additional research, you can start atScienceSource.

3. When you have come to a consensus, writedown your decision and the reasons for yourdecision.

4. Hold a town hall meeting between the variousgroups of stakeholders. Debate the pros andcons of having the fertilizer factory in yourcommunity. At the end of the debate, take avote to accept or reject the proposed factory.


B24 Skill Builder Activity

In Activity B26, you will write a procedure. Wheneveryou write a procedure, you must ensure that itincludes appropriate safety precautions. In thisactivity, you will practise writing safety precautionswhen planning a procedure for an inquiry lab.

1. Obtain a copy of the Material Safety Data Sheet(MSDS) for each of the following substances:

copper(II) sulphate (CuSO4)

hydrochloric acid (HCl)

hydrogen peroxide (H2O2)

2. For each substance, make a point-form list of themost important safety precautions.

3. Describe how you would handle each substancesafely. For example, for potassium iodide, youmight write “Use gloves when handling potassiumiodide and do not get any on your eyes, skin, orclothing.”

4. Why is it important to read the MSDS beforewriting a procedure?

5. In an investigation, copper(II) sulphate is providedin aqueous solution. Are there any safetyprecautions for solid copper(II) sulphate that donot apply to an aqueous solution of copper(II)sulphate? Explain.

Keeping Safe by Using MSDS

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B25 Design a Lab

In a single displacement reaction, one element in acompound replaces another element. Displacementreactions are used by some industries to recovermetals from solutions. For example, industries such asmining and smelting use a displacement reaction torecover copper metal from waste solutions. Copper isa valuable metal and also causes heavy-metalpollution if it is released into the environment.

In this activity, you will cover an iron nail withwater and an aqueous solution of copper(II) chloride.

QuestionWill a displacement reaction occur when an iron nail issuspended in an aqueous copper(II) chloride solution?

Design and Conduct Your Investigation

1. Consider the question, and write a prediction.

2. Write a procedure to test your prediction. Yourprocedure should have numbered steps. Whenwriting the procedure, ensure you do thefollowing:

(a) Identify the independent, dependent, andcontrolled variables.

(b) Describe how the variables will be controlled.

(c) Include all the materials and equipment youwill use. You could use a set-up similar to thatshown in Figure 6.14.

(d) Identify any safety precautions and describehow you will work safely.

(e) Describe what evidence you will look for andhow you will record your observations. You willneed to make observations over a period ofseveral days.

3. Submit your procedure to your teacher. Once yourteacher has approved your procedure, carry outyour investigation.

4. When you have completed your investigation,clean up your work area. Make sure to follow yourteacher’s directions for safe disposal of materials.Wash your hands thoroughly.

5. Analyze your results. Did you make an accurateprediction? Explain.

6. Compare your procedure with those of yourclassmates. How might you adapt or improve yourexperimental procedure?

7. Identify any new questions that arose from yourexperiment that you would like to explore.

Iron and Copper(II) Chloride

SKILLS YOU WILL USE■ Identifying variables■ Selecting instruments and

materials


Figure 6.14 This is one way that youmight set up your experiment.

• iron nail (Fe)

• 1 M copper(II) chloride(CuCl2) solution

• other materials andequipment asdetermined by thestudent


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QuestionWhat will you observe that indicates a chemicalreaction is occurring during single displacementreactions?

Procedure

1. Use a microscope or magnifying glass to makeyour observations during this procedure.

2. Put a piece of magnesium on a clean slide. Placethe slide under the microscope lens or magnifyingglass. Focus on the edge of the magnesium.

3. Using a dropper, place a drop of silver nitratesolution on the magnesium (Figure 6.15). Look forevidence that a chemical reaction is occurring. Ifyou are using a microscope, look for the growth ofmetallic crystals.

4. Record your observations.

5. Repeat steps 2 to 4 using the copper metal andthe silver nitrate solution.

6. Repeat steps 2 to 4 using the magnesium metaland the copper(II) chloride solution.



8. Did the combinations of metals and solutionsappear to react the same way? In your answer,describe and compare the speed at which anyreactions occurred and the shape of any crystalsthat formed.

9. Write a word equation, skeleton equation, andbalanced chemical equation, including states, foreach of the following:

(a) Solid magnesium metal reacts with aqueoussilver nitrate to produce solid silver metal andaqueous magnesium nitrate.

(b) Aqueous copper(II) chloride reacts with solidmagnesium metal to produce aqueousmagnesium chloride and solid copper metal.

(c) Aqueous silver nitrate reacts with solid coppermetal to produce solid silver metal andaqueous copper(II) nitrate solution.

Skill Practice

10. Why is it preferable to use a microscope to makeobservations in this investigation?

Forming Conclusions

11. For each of the metals and solutions tested, statewhether a chemical reaction occurred. Provideevidence to justify your conclusion.

Single Displacement Reactions

SKILLS YOU WILL USE■ Using equipment, materials, and

technology accurately and safely■ Processing and synthesizing data

• 1-cm2 pieces of magnesium and copper metal

• dropper

• 0.1 M silver nitrate solution

• 0.1 M copper(II)chloride solution

• microscope slides

• microscope (preferred),hand lens, ormagnifying glass



dropper

silver nitratesolution

magnesium

slide

Figure 6.15 The experimental set-up

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Key Concept Review1. Write the general chemical equation for the

combustion reactions of hydrocarbons.

2. Suppose that a friend tells you that there isonly one type of single displacement reaction.Do you agree with this statement? Explainwhy you agree or disagree.

3. Describe the similarities and differencesbetween a single displacement reaction and adouble displacement reaction.

4. What type of chemical reaction is describedby each of the following general chemicalequations?

(a) AB + CD → AD + BC

(b) HB + XOH → XB + H2O

(c) CxHy + O2 → CO2 + H2O

(d) A + BC → B + AC

(e) AB → A + B

(f) A + B → AB

5. Of the general chemical equations in theprevious question, only two include theformulas for specific compounds. Suggest areason why these are the only types ofreactions that include specific compounds inthe general chemical equation.

Connect Your Understanding6. Why are two kinds of single displacement

reactions listed in Table 6.3 on page 236?


(a) K2SO4(aq) + Al(s) →Al2(SO4)3(aq) + 2K(s)

(b) KI(aq) + Pb(NO3)2(aq) →PbI2(aq) + KNO3(aq)

(c) C4H10(aq) + O2(g) → CO2(g) + H2O(I)

(d) AgNO3(aq) + KCl(aq) →KNO3(aq) + AgCl(aq)

8. Write a balanced chemical equation for eachof the chemical reactions in the previousquestion.

9. When lithium metal and oxygen gas react,solid lithium oxide is produced. Identify thetype of chemical reaction, and then write thebalanced chemical equation.

10. When aqueous chlorine reacts with aqueouspotassium bromide, aqueous potassiumchloride and liquid bromine are produced.Identify the type of chemical reaction, andthen write the balanced chemical equation,including states.

11. When a log burns in a fireplace, as shown inthe photograph below, the hydrocarbons inthe log combine with oxygen gas in the air,producing ashes and gases.

(a) What two gases are produced?

(b) The ashes weigh much less than the logthat was burned. Does this mean that thiscombustion reaction does not follow thelaw of conservation of mass? Explain.

12. Write the balanced chemical equation for thesingle displacement reactions between each ofthe following reactants:

(a) magnesium and zinc nitrate

(b) fluorine and calcium bromide

(c) lithium and potassium chlorate

Reflection13. Did anything you learned in this section

surprise you? Why?




Question 11

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COOL IDEASfrom JAY INGRAM

Some insects bite when attacked. Some run for theirlives or fly away. Then there are others that usechemistry to protect themselves. One in particularhas been called a “champion chemist” — thebombardier beetle. This insect repels attackers witha foul chemical spray (Figure 6.16).

Here is how the beetle produces its spray. Thebeetle has two internal tanks near the tip of itsabdomen. The tanks contain the chemicalshydrogen peroxide (H2O2) and hydroquinone(C6H4(OH)2). Normally, these two chemicals just sitinside the beetle, isolated from one another.However, when the beetle feels threatened, itsqueezes the walls of the tanks. This forces thehydrogen peroxide and hydroquinone into a secondchamber where additional chemicals are stored.When all these chemicals combine, a series ofchemical reactions occur.

One reaction releases oxygen (O2) from thehydrogen peroxide. The hydroquinone reacts withthe oxygen, which produces an evil-smelling andnoxious chemical called benzoquinone (C6H4O2).The benzoquinone then explodes out the rear end ofthe beetle with a loud popping sound!

Close inspection reveals that the popping sound isnot a single explosion. The beetle produces a rapidseries of explosions — 500 to 1000 every second,similar to the firing of a machine gun. The chemicalreaction also generates heat, so the chemical sprayemerges from the beetle at about the temperature ofboiling water.

The beetle is incredibly accurate when it releasesits spray, thanks to special nozzles in the beetle’sbody. These nozzles allow the beetle to spraywhatever is attacking it. Since the spray is hot andtoxic, the beetle itself would be damaged if thechemicals combined and did not leave its body.

Most insects or frogs will drop the beetle when itsprays them. However, one species of toad, Bufomarinus, swallows the beetle in a quick gulp, beforethe beetle can fire (Figure 6.17). If you listen closely,you can hear the popping coming from inside thetoad’s stomach!

Question1. Summarize this reading. Include a main idea

and two points that support it.

The Bombardier Beetle

Figure 6.16 The bombardier beetle emits a toxic spray that isproduced by a series of chemical reactions inside its body.

Figure 6.17 This species of toad, Bufo marinus, is able to eatthe bombardier beetle before it sprays.

Jay Ingram is an experienced science journalist, author of TheDaily Planet Book of Cool Ideas,and host of the Daily Planet onDiscovery Channel Canada.


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242 UNIT B

Key Concept Review1. What is the opposite of a decomposition

chemical reaction?

2. The prefix “syn-” means “together.” Explainwhy this is a suitable prefix for describing asynthesis chemical reaction.

3. What are the two types of displacementchemical reactions?

4. What is the general formula for a hydrocarboncompound?

5. From what are fossil fuels formed?

6. Name the six different types of chemicalreactions discussed in chapter 6.

7. In which two types of chemical reactions iswater always produced?

8. Which type of chemical reaction is describedby each of the following general chemicalequations?

(a) AB + CD → AD + BC

(b) HB + XOH → XB + H2O

Connect Your Understanding9. Suggest two or more reasons why it is

important for chemists to study manyexamples of the different types of chemicalreactions you learned about in this chapter.

10. Name the product in each of the followingreactions:

(a) potassium and iodine →

(b) cesium and chlorine →

11. What two compounds are always produced bythe combustion of hydrocarbons andcarbohydrates?

12. Magnesium chloride can undergo adecomposition reaction to produce magnesiummetal and chlorine gas. Write the wordequation, skeleton equation, and balancedchemical equation for this reaction.

13. The gas rising from the beaker in thephotograph below is carbon dioxide.Combustion reactions produce carbon dioxidegas, CO2. Why are these reactions of concernto people who care about changes in Earth’satmosphere?

14. The types of chemical reactions discussed inchapter 6 can be classified by the nature of thereactants. Identify the type of chemicalreaction that would occur between thefollowing reactants:

(a) Li(s) + O2(g) →

(b) NaCl(s) →

(c) K2SO4(aq) + Al(s) →

(d) CaBr2(aq) + Ba(NO3)2(aq) →

(e) C4H10(aq) + O2(g) →

(f) AgNO3(aq) + KCl(aq) →

(g) NI3(aq) →

15. Identify the type of chemical reactiondescribed by the skeleton equation below.Then, write the balanced equation. FeCl2(aq) + K2S(aq) → FeS(s) + KCl(aq)

a

a

a

a

a

a

a

k

k

k

k

k

k

t

k




tk

6 CHAPTER REVIEW

Question 13

ist10_ch06.qxd 7/22/09 3:35 PM Page 242


The Scientist’s Approach toWriting

Make a list of what you learned about important

features of scientific writing. Write a paragraph

reflecting on how writing for science class is different

from writing that you might do in English or history

class. Share your thoughts with a partner.

After Writing

Unit Task Link

Apply your knowledge of types of reactions to classify

and predict the outcome of these reactions, all of

which are part of the Unit Task:

Mg + HCl → ?

MgSO4 + Na2CO3 → ?

Mg + CuCl2 → ?

In the Unit Task, you will have an opportunity to

carry out these reactions and observe them in the

laboratory.

16. In the previous question, the reaction takesplace in water. Which substance would you beable to see in the container? Explain how youknow.

17. Classify each of the following reactions, andbalance the equations.

(a) CaCl2(g) → Ca(s) + Cl2(g)

(b) NaN3(s) → Na(s) + N2(g)

(c) Pb(NO3)2(aq) + Cu2SO4(aq) →PbSO4(s) + CuNO3(aq)

(d) Ni2O3(s) → Ni(s) + O2(g)

(e) CH4(g) + O2(g) → CO2(g) + H2O(g)

(f) NaI(aq) + AlCl3(aq) → NaCl(aq) + AlI3(s)

18. Classify each of the following reactions, andwrite a balanced chemical equation for each.

(a) sodium sulphate + calcium chloride →sodium chloride + calcium sulphate

(b) magnesium + nitrogen →magnesium nitride

(c) strontium hydroxide + lead(II) bromide → strontium bromide + lead(II) hydroxide

(d) sodium + oxygen → sodium oxide

(e) nitrogen + hydrogen → ammonia (NH3)

(f) hydrogen chloride → hydrogen + chlorine

(g) aluminum iodide + bromine →aluminum bromide + iodine

(h) hydrochloric acid + sodium hydroxide →sodium chloride + water

19. Calcium metal reacts with iodine to producecalcium iodide. Identify the type of chemicalreaction. Then, write a balanced chemicalequation for this reaction.

20. When zinc metal is mixed with aqueouscopper(II) sulphate, copper metal and aqueouszinc sulphate are produced. Identify the type ofchemical reaction and then write the balancedchemical equation.

21. Several compounds made up of a metallicelement combined with bromine are used inwater treatment facilities, includingmagnesium bromide. Write the balancedchemical equation, including states, for theformation of solid magnesium bromide from magnesium and bromine.

22. When aqueous zinc bromide and aqueous silver nitrate react, solid silver bromide andaqueous zinc nitrate are produced. Identify the type of chemical reaction, and then write a word equation, skeleton equation, andbalanced chemical equation for the reaction.Include states.

23. Suppose that a classmate tells you “In aneutralization reaction, you always have tostart with two compounds.” Is your classmate correct? Support your answer.

Reflection24. Of the six types of chemical reactions that you

learned about in this chapter, which do youthink is most important to society? Givereasons for your answer. c

t

a

a

a

a

a

a

a

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244 UNIT B

BU N I T

Summary

• Chemical change

• Ions and molecules

• Ionic and molecular compounds

• Law of conservation of mass

• Balanced chemical equations

• During a chemical reaction, new substances are formed that have differentproperties from the reactants. (4.1)

• Metallic atoms form positive ions; non-metallic atoms form negative ions.(4.2)

• Polyatomic ions are charged groups of atoms. (4.2)

• Ionic compounds form between metals and non-metals. (4.2)

• Molecular compounds form between non-metals and non-metals. (4.2)

• The reactant(s) in a chemical reaction undergo chemical change(s). Theproduct(s) of a chemical reaction have different properties than thereactant(s). (4.3)

• The law of conservation of mass states that mass will remain constantduring any chemical reaction. (4.3)

• A word equation describes a chemical reaction using words. (4.3)

KEY CONCEPTS CHAPTER SUMMARY

• Properties of acids and bases

• pH scale

• Measuring pH

• Neutralization

• The pH of liquids can be determined using pH indicators. (5.1)

• An acid has a pH less than 7, a base has a pH greater than 7, and aneutral liquid has a pH equal to 7. (5.1)

• Neutralization is a chemical reaction between an acid and a basethat produces water and a salt. (5.2)

• Neutralization reactions can be used to help solve chemicalcontamination problems in the environment. (5.2)

• General chemical equations

• Types of chemical equations:

• Synthesis

• Decomposition

• Combustion

• Single displacement

• Double displacement

• A general chemical equation (GCE) is an equation that uses lettersof the alphabet (A, B, C, D, X), as well as some element symbols, torepresent different chemical reactions. (6.1)

• In a synthesis reaction, two or more elements combine to produceat least one new substance. (6.1)

• In a decomposition reaction, a single compound is broken down intoits elements. (6.1)

• A combustion reaction always involves oxygen as a reactant andcarbon dioxide and water as products. (6.2)

• In a single displacement reaction, a reactive metallic element canreplace a less reactive metallic element in a compound. (6.2)

• In a double displacement reaction between two ionic compounds,the positive or negative ions switch places. (6.2)

Chemical change occurs during chemical reactions.4

Acids and bases are important to our health, industries, and environment.5

Chemical reactions can be grouped according to the characteristics of their 6

ist10_ch06.qxd 7/22/09 3:35 PM Page 244

245UNIT B Summary

• alkali metal (p. 148)• alkaline earth metal (p. 148)• atom (p. 144)• atomic mass (p. 149)• atomic number (p. 149)• atomic theory (p. 144)• Bohr diagram (p. 145)• chemical change (p. 174)• chemical equation (p. 175)• chemical property (p. 142)• chemical reaction (p. 174)• compound (p. 143)• covalent bond (p. 164)• diatomic molecule (p. 164)• electron (p. 144)• element (p. 143)• family (p. 146)

VOCABULARY KEY VISUALS

• acid (p. 196)

• acid leaching (p. 211)

• acid precipitation (p. 208)

• acid-base indicator (p. 197)

• base (p. 197)

• neutral (p. 196)

• neutralization (p. 206) ph scale

• combustion (p. 232)

• decomposition reaction (p. 226)

• double displacementreaction (p. 235)

• fossil fuel (p. 232)

• general chemical equation(GCE) (p. 224)

• hydrocarbon (p. 232)

• single displacement reaction(p. 233)

• synthesis reaction (p. 225)

Single displacement

Double displacement

reactants and products.

B ABA

B AB A

Decomposition

AB + CD → AD + CB

AB + C → AC + B

AB + C → CB + A

Synthesis

• pH scale (p. 196)

• precipitate (p. 206)

• universal indicator (p. 197)

• halogen (p. 146)• heterogeneous mixture

(p. 143)• homogeneous mixture

(p. 143)• ion (p. 149)• ionic compound (p. 156)• law of conservation of mass

(p. 176)• matter (p. 142)• mechanical mixture (p. 143)• metal (p. 146)• metalloid (p. 146)• mixture (p. 143)• molecular compound (p. 165)• molecular element (p. 164)• molecule (p. 164)

• multivalent element (p. 157)

• non-metal (p. 146)• nucleus (p. 144)• period (p. 146)• physical property (p. 142)• polyatomic ion (p. 160)• product (p. 174)• proton (p. 144)• pure substance (p. 143)• reactant (p. 174)• shell (p. 144)• skeleton equation (p. 178)• state (p. 142)• suspension (p. 143)• valence electron (p. 145)• valence shell (p. 145

→

→

1 molecule of CI2: 2 chlorine atoms share 1 electron each to form 1 pair of shared electrons

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14moreacidic

2.0lemon juice

4.2 tomatoes

6.0 milk

neutral

8.2 baking soda

10 toothpaste

12ammonia

13.8 drain

cleaner

morebasic

0.5battery acid

7.0pure water

5.0acid rain

5.6 normal

rain8.0

seawater

2.2vinegar

1.0stomach acid

Cl-

1-

Na+

1+

A molecular compound

An ionic compound

ist10_ch06.qxd 7/22/09 3:35 PM Page 245

BU N I T

Task

246 UNIT B Task

Magnesium isthe eighth mostabundantelement inEarth’s crust. Itis not usuallyfound in itselemental form.

CAUTION• Follow your teacher’s safety instructions for each

chemical reaction.• Avoid touching all reactants and products.• Tie back long hair and secure any loose clothing before

working around an open flame.Criteria for Success

• You must identify whether each reactant is anelement, an ionic compound, a molecularcompound, an acid, or a base.

• You must predict the products of each reaction.

• You must provide written observations, as well asword equations and balanced chemical equationsshowing states, for each reaction.

Classifying Chemical Reactions Involving Magnesium

• 10-mL graduated cylinder

• 1 M hydrochloric acid solution, HCl(aq)

• 3 test tubes

• 3-cm strips of Mg metal ribbon

• balance

• 3 scoopulas

• magnesium sulphate, MgSO4(s)

• water, H2O(l)

• 3 test-tube stoppers

• test-tube rack

• sodium carbonate, Na2CO3(s)

• copper(II) chloride, CuCl2(s)

What You Need

Getting StartedIn this unit, you have learned how to identify substancesfrom their names and formulas, how to write wordequations and balanced chemical equations, and how toidentify six types of chemical reactions. In this Unit Task,you will apply this knowledge in carrying out a procedureto observe chemical reactions involving magnesium.

Your GoalsYou will carry out several chemical reactions involvingmagnesium and classify each type of reaction. You willthen write word equations and balanced chemicalequations for each chemical reaction.

What You Need to KnowThe six types of chemical reactions that you learnedabout in this unit are neutralization reactions, synthesisreactions, decomposition reactions, combustionreactions, single-displacement reactions, and double-displacement reactions.

Procedure

1. For each of the substances listed in the What YouNeed, identify whether each is an element, an ioniccompound, a molecular compound, an acid, or abase. If a substance is an ionic compound, statewhether it contains a polyatomic ion.

2. Read over the remaining steps of the procedure.Write a prediction of the type of reaction that willoccur for each chemical reaction you will carry out.

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247UNIT B Task

Part 1 — Reaction 1

3. Using the graduated cylinder, measure 5 mL of thehydrochloric acid and then pour it into a test tube.Drop in a piece of magnesium ribbon. Add a secondpiece so you can see the reaction again. Recordyour observations.


4. Using the balance and a clean scoopula, weigh out 1 g of magnesium sulphate and then place it in atest tube. Using the graduated cylinder, measure 10 mL of water and add it to the test tube. Stopperthe test tube, and shake it to dissolve themagnesium sulphate. Place the test tube in the test-tube rack.

5. Using the balance and a clean scoopula, weigh out 1 g of sodium carbonate and place it in a test tube.Using the graduated cylinder, measure 10 mL ofwater and add it to the test tube. Stopper the testtube, and shake it in order to dissolve the sodiumcarbonate. Place the test tube in the test-tube rack.

6. Mix the magnesium sulphate solution and sodiumcarbonate solution together by pouring the contentsof one test tube into the other. Record yourobservations.


7. Using the balance and a clean scoopula, weigh outa 1 g quantity of copper(II) chloride crystals andplace it in a test tube. Using the graduated cylinder,measure 10 mL of water and add it to the test tube.Stopper the test tube, and shake it in order todissolve the copper(II) chloride.

8. Drop in a piece of magnesium ribbon. Record yourobservations.


Assessing Your Work

10. In reaction 1, the hydrogen in the hydrochloric acidbehaves chemically like a metal. What type ofreaction is this? Write the word equation and thebalanced chemical equation for this reaction.

11. In reaction 2, a white precipitate was observed.What is the identity of this precipitate? What type ofreaction is this? Write the word equation and thebalanced chemical equation for this reaction.

12. In reaction 3, one of the products is copper metal.The other is magnesium chloride. What type ofreaction is this? Write the word equation and thebalanced chemical equation for this reaction.

13. Write a summary report. Your report should includethe type of substance for each reactant, your initialpredictions, and whether each prediction wascorrect. It should also include your observations andthe word and balanced chemical equations for eachreaction.

In step 6, mix the two solutions by pouring the contents of one testtube into the other.

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UNIT B Review

Key Terms Review1. Create a mind map that illustrates your

understanding of the following terms andhow they relate to chemical reactions.

Key Concept Review

Chemical change occurs duringchemical reactions.

2. Write the symbols for the following ions.

(a) cesium (d) nickel(III)

(b) oxide (e) titanium(IV)

(c) tin(II)

3. Write the name of the following ions.

(a) Mg2+ (d) Ag+

(b) F– (e) N3–

(c) Au+

4. (a) What kind of electric charge do metallicions possess?

(b) What kind of electric charge do non-metallic ions possess?

5. What is a molecule?

6. (a) What is a valence shell?

(b) What are valence electrons?

7. What is the difference between a moleculethat is an element and a molecule that is acompound?

8. How many occupied shells are there in a neonatom?

9. What kinds of elements combine to formionic compounds?

10. What kinds of elements combine to formmolecular compounds?


12. What information does a word equationcontain?

13. Where are the reactants and the productslocated in a chemical equation?

14. How do the properties of ionic and molecularcompounds differ? t

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U N I T

acidacid-base indicatoratombalanced chemical equationbasebinary compoundchemical formulachemical reactioncombustion reactioncompounddecomposition reactiondouble displacement reactionelementionionic compoundlaw of conservation of massmattermetalsmolecular compoundneutralizationnon-metalspHpolyatomic ionproductpure substancereactantsaltsingle displacement reactionsynthesis reactionvalence shellword equation




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B Review

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Acids and bases are important to ourhealth, industries, and environment.

15. What is the typical range of numbers on thepH scale?

16. What is the pH range of bases?

17. What is the pH range of acids?

18. What kinds of substances are the reactants ina neutralization reaction?

19. In which type of chemical reaction is an ioniccompound called a salt always produced?

20. How can you identify an acid and a base fromtheir chemical formulas? (Two answers arerequired.)

21. What is acid precipitation?

22. What would the pH of a neutral liquid be?

23. (a) What are scrubbers?

(b) Where would they be used?

Chemical reactions can be groupedaccording to the characteristics of theirreactants and products.

24. What is a general chemical equation?

25. What type of chemical reaction is theopposite of a synthesis reaction?

26. What type of chemical reaction is representedby these general chemical equations?

(a) A + B → AB

(b) CxHy + O2 → CO2 + H2O

27. Complete and balance each equation below.The products are all solid ionic compounds.

(a) Na + Br2 →

(b) Mg + F2 →

(c) Al + Cl2 →

(d) K + N2 →

(e) Ca + P4 →

28. Suppose the reactants of a chemical reactioninclude a compound and a metallic element.What type of chemical reaction will occur?

29. Suppose the products of a chemical reactionare carbon dioxide and water. What kind ofchemical reaction occurred?

Connect Your Understanding

30. Name three elements that form positivelycharged ions.

31. Name three elements that form negativelycharged ions.

32. The figure below shows a Bohr diagram of acalcium atom.

(a) How many electron shells are shown?

(b) How many valence electrons are in thevalence shell?

(c) The charge on a calcium ion is 2+.Explain how this diagram might havebeen used to predict this charge.

33. Do ionic compounds form molecules?Explain. a

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Ca atom20 protons

20 electrons

Question 32a

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UNIT B Review

34. What is the only common positively chargedpolyatomic ion? Provide its name and ionsymbol.

35. Draw and label a diagram to show electrontransfer from the metallic atom to the non-metallic atom to form the compoundlithium fluoride.

36. Draw a Bohr diagram that shows how a pairof electrons is shared in a molecule ofhydrogen fluoride (HF).

37. Some sites on the Internet have a FAQ(frequently asked questions) page thatcontains several questions along with theanswers. Design and create a FAQ page forbalancing chemical equations. Be creative: addappropriate, relevant images so that your Webpage is attractive and informative.

38. Suppose that a student placed a small piece oflithium metal into a beaker of water. Thestudent observed a chemical reaction, inwhich a hissing sound was produced alongwith bubbles. Decide if these changes couldindicate a chemical reaction. Then, explainyour thinking.

39. Suppose you are given a formula equation andare told that it has been balanced. How canyou determine whether it has been balancedcorrectly?

40. Suggest how each of the following acidsobtains its name, by providing the name ofone or more elements in each:

(a) sulphuric acid, H2SO4

(b) hydrochloric acid, HCl

(c) nitric acid, HNO3

(d) phosphoric acid, H3PO4

41. A home gardener wants to raise the pH ofsome soil. What type of chemical might beused? Give at least one specific example.

42. Predict how acid precipitation might causechanges that affect the organisms in a lake.


(a) NiCO3(aq) + Fe(s) → FeCO3(aq) + Ni(s)

(b) C5H10(l) + O2(g) → CO2(g) + H2O(l)

(c) Li4C(s) + Ca(s) → Li(s) + Ca2C(s)

(d) C6H14(g) + O2(g) → CO2(g) + H2O(l)

(e) CsF(aq) + AlBr3(aq) → CsBr(aq) + AlF3(s)

44. Write a word equation and a balancedchemical equation, including states, for thechemical reactions (a), (c), and (e) in theprevious question.

45. Calcium bromide is used in some medicinesand as a food preservative. Write the wordequation, skeleton equation, and balancedchemical equation for the synthesis reactionthat produces calcium bromide.

46. Contrast the two types of single displacementchemical reactions.

47. What does a combustion reaction have incommon with a neutralization reaction?

48. Using a T-chart with two columns, list thesimilarities and differences between asynthesis reaction and a single displacementreaction.

49. Write the names of the following ioniccompounds.

(a) BeO (f) MnCl2(b) KCl (g) K2SO4

(c) SrBr2 (h) Li3PO4

(d) Al2S3 (i) Cr(OH)2

(e) Ca3P2 (j) NH4HCO3

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U N I TB Review (continued)

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50. Write the formulas for the following ioniccompounds.

(a) sodium bromide

(b) beryllium phosphide

(c) copper(I) oxide

(d) palladium(IV) nitrate

(e) ammonium sulphate

(f) ammonium nitrate

51. Write the names of the following binarymolecular compounds:

(a) S2O3

(b) P2S5

(c) OF2

(d) N2O3

(e) CO2

52. Write the formulas of the following binarymolecular compounds:

(a) sulphur hexafluoride

(b) carbon disulphide

(c) dinitrogen monoxide

(d) carbon tetrachloride

(e) carbon monoxide

53. For each of the following word equations,identify the type of chemical reaction itrepresents.

(a) methane (CH4) + oxygen →carbon dioxide + water

(b) barium + oxygen → barium oxide

(c) aluminum bromide + fluorine →aluminum fluoride + bromine

(d) magnesium chloride →magnesium + chlorine

(e) lithium sulphate + barium chloride →lithium chloride + barium sulphate

(f) nitric acid + barium hydroxide →barium nitrate + water

54. Rewrite this balanced chemical equation. Fillin the missing salt compound (given by “?”)on the products side.

HCl + KOH → ? + H2O

55. Create an analogy by describing an event oractivity in your daily life that is similar to asingle displacement reaction.

56. The following general chemical equations usepicture symbols in place of chemical symbols.Identify the chemical reaction represented byeach.

(a) ■ + ▲�� → ■��+ ▲

(b) H��+ �OH →��+ H2O

(c) ��→ �+ �

(d) �+ ■�→��+ ■

(e) ��+�→ ��

(f) ��+ ��→��+ ��

(g) ■OH + H��→ ■��+ H2O

57. For each general chemical equation in theabove question, find one example of abalanced chemical equation in this unit.

58. When calcium metal undergoes a chemicalreaction with oxygen gas, solid calcium oxideis produced. Identify the type of chemicalreaction, and then write the balancedchemical equation.

59. Write the skeleton equation and balancedchemical equation for each of the followingchemical reactions.

(a) carbon disulphide + oxygen →carbon dioxide + sulphur dioxide

(b) lead(II) nitrate + sodium sulphate →lead(II) sulphate + sodium nitrate

(c) potassium bromide + silver nitrate →silver bromide + potassium nitrate

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UNIT B Review

60. Which of the chemical reactions in question 59 would be classified as a double-displacement reaction?

61. A chemist carefully combines sulphuric acid(H2SO4) and ammonium hydroxide. Write theword equation, skeleton equation, andbalanced chemical equation for thisneutralization reaction.

62. Benzene, C6H6, is a toxic liquid hydrocarbonthat is used to produce plastics, adhesives,nylon, detergents, dyes, lubricants, explosives,and pesticides. Write the word equation,skeleton equation, and balanced chemicalequation for the combustion of benzene.

63. For each of the following, suggest one or moresituations in which chemical reactions areimportant.

(a) in your home

(b) at tourist resorts

(c) in restaurants in your community

(d) in another situation of your choice

64. Name several categories of consumerproducts that are produced through chemicalreactions.

65. Suggest several ways that you can keepinformed about chemicals and chemicalreactions.

66. Pure substances are used to producenewspapers, paper towels, clothing, and manyconsumer products you use daily. Whathappens to these pure substances when youno longer need these products? Suggestseveral answers.

67. Every Canadian province has emergencyteams and procedures to deal with chemicalspill situations. Why do you think it isimportant to have laws that cover an entireprovince?

68. Suppose a train derailment spills sodiumhydroxide into some soil. Use your knowledgeof chemical reactions to suggest how anemergency response team could neutralize theeffects of this chemical.

69. Write an e-mail to a friend in which youdescribe two or more applications of chemicalreactions in daily life

70. Name five or more jobs or professions whereit would be important to know aboutchemical reactions.

71. The pulp and paper industry uses a numberof different chemicals. The table below listssome of these chemicals and describes howthey are used.

(a) Suggest several reasons why thesechemicals are reused as often as possible.

(b) Since the pulp and paper manufacturersreuse chemicals, if you reduce your use ofpaper products, will this affect theamount of chemicals that are used inmaking pulp and paper? Explain. a

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U N I TB Review (continued)

Substance Formula Use

barium sulphate BaSO4 provides white colourto paper

caustic lye (sodiumhydroxide)

NaOH maintains correct pH

chalk (calciumcarbonate)

CaCO3 makes paper lookbrighter

Some Chemicals Used in the Pulp and Paper Industry

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72. Suggest one or more reasons why a career inchemistry or chemical engineering can berewarding.

73. Suppose you are a member of the localgovernment in your community. A companyhas indicated that it is interested in opening achemical manufacturing facility in yourcommunity. The facility will offer year-roundemployment to many people. What additionalinformation will you need in order to decidewhether to allow the facility to be located inyour community?

Skills Practice74. Write a brief procedure to test whether an

unknown liquid is acidic, basic, or neutral.Include any safety precautions.

75. Several groups of students performed thefollowing investigation. Two beakers, eachcontaining a colourless liquid, were weighed.The total mass was recorded. The two liquidswere then combined, and a white solid wasobserved to form. The two beakers, one ofwhich contained the solid product, were thenreweighed and the total mass recorded. Eachgroup then compared the total mass beforeand after the chemical reaction had occurred.Most found that the total mass had notchanged. However, some groups found thatthe mass decreased slightly. Suggest possiblereasons for these observations.

Revisit the Big Ideas and FundamentalConcepts76. Use the new terms and concepts you have

learned in this unit to design and draw amind map for the entire unit. You may usethe titles of the chapters for the separatesections of your map. Add relevant detailsand information from activities and/orresearch you have completed. Add relevantimages. Include your name and class toidentify your map.

Science, Technology, Society,and the Environment

77. Consider the products of a combustionreaction. How could you and your family helpto reduce global warming? Be specific.

78. Why is acid rain less of a problem in Ontarioin the 21st century than in the centurybefore? Provide several answers, including atechnology.

79. Describe one or more aspects of your lifestylethat you could alter to reduce the number ofchemical reactions your daily activitiesrequire.

Reflection80. In this unit, you have learned many things

about how chemical reactions form. What isthe most important thing you learned aboutchemical reactions? Why do you think it isthe most important?

81. Think back to your ideas about the effects ofchemical reactions on the environment at thestart of this chapter. How have your ideaschanged? c

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253UNIT B Review

STSE

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Chemical Reaction

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