54 Chapter 3
What Yoursquoll LearnYou will distinguishbetween physical andchemical properties
You will classify matter bycomposition element com-pound or mixture
You will identify observablecharacteristics of chemicalreactions
You will explain the funda-mental law of conservationof mass
Why Itrsquos ImportantYou are completely sur-rounded by matter To betterunderstand this mattermdashhowit affects you how you affectit and how it can be manipu-lated for the benefit of soci-etymdashyou need to build a basicunderstanding of the typesand properties of matter
MattermdashProperties andChanges
CHAPTER 3
Visit the Chemistry Web site atchemistrymccom to find linksabout matter properties andchanges
Chemistry is the study of matterand its properties Every aspect ofthese diversrsquo environment underwater and on land is some formof matter
null
12173093
null
6316459
31 Properties of Matter 55
DISCOVERY LAB
Materials
large test tubetest-tube holder or rack10 mL HClzinc metalwood splintmatch or burner
Observing Chemical Change
Consider the metal objects that are part of the everyday world Amailbox for example stands outside day in and day out without
seeming to change Under what conditions does metal exhibit chem-ical change
Safety Precautions
Procedure
1 Place a piece of zinc metal in a large test tube
2 Add approximately 10 mL of 3M hydrochloric acid (HCl) to the testtube Record your observationsCAUTION HCI causes burns and hazardous fumes
3 When the zinc and HCl have reacted for approximately 1 minbring a lighted glowing wood splint to the mouth of the testtube CAUTION Be sure the test tube is facing away from yourface when the splint is brought near Again record yourobservations
Analysis
What may have caused the dynamic reaction you observed in step 3Did you expect this reaction Explain
Always wear eye goggles gloves and anapron when experimenting with chemicalsUse caution when handling an open flame
Objectivesbull Identify the characteristics
of a substance
bull Distinguish between physi-cal and chemical properties
bull Differentiate among thephysical states of matter
Vocabularysubstancephysical propertyextensive propertyintensive propertychemical propertystates of mattersolidliquidgasvapor
Section 31 Properties of Matter
Imagine yourself scuba diving through a complex biological ecosystem suchas a coral reef What kinds of things fill your imagination Regardless of whatyou envision there is only one answermdashyou see matter The diversity of mat-ter in the world and in the universe is astounding From pepperoni pizzas tosupernovas itrsquos all matter If we are to understand this diversity we must startwith a way of organizing and describing matter
SubstancesRecall from Chapter 1 that chemistry is the study of matter and matter isanything that has mass and takes up space Everything around you is mat-ter including things such as air and microbes which you cannot see Forexample table salt is a simple type of matter that you are probably familiarwith Table salt has a unique and unchanging chemical composition It isalways 100 sodium chloride and its composition does not change from onesample to another Matter that has a uniform and unchanging compositionis called a substance also known as a pure substance Table salt is a sub-stance Another example of a pure substance is water Water is always com-posed of hydrogen and oxygen Seawater on the other hand is not asubstance because samples taken from different locations will probably have
null
9278609
differing compositions That is they will contain differing amounts of watersalts and other dissolved substances Given this definition what other puresubstances are you familiar with Substances are important much of yourchemistry course will be focused on the processes by which substances arechanged into different substances
Physical Properties of MatterYou are used to identifying objects by their propertiesmdashtheir characteristicsand behavior For example you can easily identify a pencil in your backpackbecause you recognize its shape color weight or some other property Thesecharacteristics are all physical properties of the pencil A physical propertyis a characteristic that can be observed or measured without changing the sam-plersquos composition Physical properties describe pure substances too Becausesubstances have uniform and unchanging compositions they have consistentand unchanging physical properties as well Density color odor taste hard-ness melting point and boiling point are common physical properties thatscientists record as identifying characteristics of a substance Sodium chlo-ride forms solid white crystals at room temperature all having the sameunique salty taste Table 3-1 lists several common substances and their phys-ical properties
Extensive and intensive properties Physical properties can be furtherdescribed as being one of two types Extensive properties are dependent uponthe amount of substance present For example mass which depends on theamount of substance there is is an extensive property Length and volume arealso extensive properties Density on the other hand is an example of an inten-
sive property of matter Intensive properties are independentof the amount of substance present For example density of asubstance (at constant temperature and pressure) is the sameno matter how much substance is present
A substance can often be identified by its intensive prop-erties In some cases a single intensive property is uniqueenough for identification During the California gold rushminers relied on goldrsquos characteristic density (19 gcm3) toseparate valuable gold-containing flakes from riverbed sandThe process used by the miners is shown in Figure 3-1Another intensive property of gold is its distinctiveappearance Unfortunately miners often learned that iden-tification of gold based on appearance alone was mislead-ing Figure 3-2 shows a nugget of the relatively worthless
56 Chapter 3 MattermdashProperties and Changes
Figure 3-1
Miners relied on the physicalproperty of density to distin-guish gold (19 gcm3) from theworthless minerals in their sluicepans The density of pyrite aworthless mineral often mis-taken for gold is 5 gcm3
Physical Properties of Common Substances
State Melting Boiling DensitySubstance Color at 25degC point (degC) point (degC) (gcm3)
Oxygen Colorless Gas 218 ndash183 00014
Mercury Silver Liquid ndash39 357 135
Water Colorless Liquid 0 100 100
Sucrose White Solid 185 Decomposes 159
Sodium White Solid 801 1413 217chloride
Table 3-1
Science WriterDo you get excited about newsin science and technology Doyou like to explain informationin a way that others find inter-esting and understandableThen consider a career as a science writer
Science writers keep up-to-dateon what is happening in theworld of science and translatethat news so nonscientists canunderstand it These writerswork for newspapers maga-zines scientific publicationstelevision stations and Internetnews services Lots of curiosityas well as a degree in a scienceandor journalism is essential
null
17768661
mineral pyrite often called ldquofoolrsquos goldrdquo which looks very similar to actualgold nuggets Such errors in identification based on the intensive property ofappearance fooled many miners into falsely thinking they had struck it rich
Chemical Properties of MatterSome properties of a substance are not obvious unless the substance haschanged composition as a result of its contact with other substances or theapplication of thermal or electrical energy The ability of a substance to com-bine with or change into one or more other substances is called a chemicalproperty The ability of iron to form rust when combined with air is anexample of a chemical property of iron Similarly the inability of a substanceto change into another substance is also a chemical property For examplewhen iron is placed in nitrogen gas at room temperature no chemical changeoccurs The fact that iron does not undergo a change in the presence of nitro-gen is another chemical property of iron
Observing Properties of MatterEvery substance has its own unique set of physical and chemical propertiesTable 3-2 lists several of these properties of copper Figure 3-3 shows phys-ical and chemical properties of copper What physical and chemical proper-ties are evident in these photos
31 Properties of Matter 57
Figure 3-3
These photos illustrate some ofthe physical and chemical prop-erties of copper as it exists inthe form of hardware andthe Statue of Liberty b
a
Figure 3-2
Gold and pyrite or foolrsquosgold have similar physicalproperties but are different samples of matter
ba
Properties of Copper
Physical properties Chemical properties
Table 3-2a
b
a bGold Pyrite
bull Reddish brown shiny
bull Easily shaped into sheets (malleable) and drawn into wires(ductile)
bull Good conductor of heat and electricity
bull Density 892 gcm3
bull Melting point 1085degC
bull Boiling point 2570degC
bull Forms green copper carbonate compound when in contact withmoist air
bull Forms new substances when com-bined with nitric acid and sulfuricacid
bull Forms a deep blue solution whenin contact with ammonia
null
85837875
Observations of properties may vary depending on the conditions of theimmediate environment It is important to state the specific conditions inwhich observations are made because both chemical and physical propertiesdepend on temperature and pressure Consider the properties of water forexample You may think of water as a liquid (physical property) that is notparticularly chemically reactive (chemical property) You may also know thatwater has a density of 100 gcm3 (physical property) These properties how-ever apply only to water at standard ldquoroomrdquo temperature and pressure At tem-peratures greater than 100degC water is a gas (physical property) with a densityof about 00006 gcm3 (physical property) that reacts rapidly with many dif-ferent substances (chemical property) As you can see the properties of waterare dramatically different under different conditions
States of MatterImagine you are sitting on a bench breathing heavily and drinking water aftera tiring game of soccer In this scenario you are in contact with three differentforms of matter the bench is a solid the water is a liquid and the air you breatheis a gas In fact all matter that exists on Earth can be classified as one of thesephysical forms called states of matter Scientists recognize a fourth state ofmatter called plasma but it does not occur naturally on Earth except in the formof lightning bolts The physical state of a substance is a physical property ofthat substance Each of the three common states of matter can be distinguishedby the way it fills a container
Solids A solid is a form of matter that has its own definite shape and vol-ume Wood iron paper and sugar are examples of solids The particles ofmatter in a solid are very tightly packed when heated a solid expands butonly slightly Because its shape is definite a solid may not conform to theshape of the container in which it is placed The tight packing of particles ina solid makes it incompressible that is it cannot be pressed into a smallervolume It is important to understand that a solid is not defined by its rigid-ity or hardness the marble statue in Figure 3-4 is rigid whereas wax sculp-ture is soft yet both are solids
Liquids A liquid is a form of matter that flows has constant volume andtakes the shape of its container Common examples of liquids include waterblood and mercury The particles in a liquid are not rigidly held in placeand are less closely packed than are the particles in a solid liquid particles
58 Chapter 3 MattermdashProperties and Changes
Figure 3-4
The properties of the solidmaterials marble and waxmake these sculptures possibleParticles in a solid are tightlypacked giving definite shapeand volume to the solid
c
ba
Solid
a b
c
null
17444711
31 Properties of Matter 59
Figure 3-5
Despite having differentshapes each of these measuringcups holds the same volume ofliquid
River water flows to fitwithin the boundaries of itsbanks regardless of the curvesalong its path
Molecules in a liquid areclosely packed but can still moverelatively freely
c
b
a
Liquid
a bc
Figure 3-6
Molecules in a gas are farapart and freely moving
Neon gas completely fills the tubes of the electricartwork
b
a
are able to move past each other This allows a liquid to flow and take theshape of its container although it may not completely fill the container Aliquidrsquos volume is constant regardless of the size and shape of the containerin which the liquid is held the volume of the liquid remains the same Thisis why measuring cups used in cooking such as those pictured in Figure3-5 can be made in a variety of shapes yet still measure the same volumeBecause of the way the particles of a liquid are packed liquids are virtu-ally incompressible Like solids liquids tend to expand when heated
Gases A gas is a form of matter that flows to conform to the shape of itscontainer and fills the entire volume of its container Examples of gasesinclude neon which is used in the lighted artwork in Figure 3-6 methanewhich is used in cooking and air which is a mixture of gases Compared tosolids and liquids the particles of gases are very far apart Because of the sig-nificant amount of space between particles gases are easily compressed Theproblem-solving LAB in this section poses several important questions aboutthe practical use of compressed gas
It is likely that you are familiar with the word vapor as it relates to theword gas The words gas and vapor while similar do not mean the samething and should not be used interchangeably The word gas refers to a sub-stance that is naturally in thegaseous state at room temperatureThe word vapor refers to thegaseous state of a substance that isa solid or a liquid at room tempera-ture For example steam is a vaporbecause at room temperature waterexists as a liquid
bGasa
null
11253363
60 Chapter 3 MattermdashProperties and Changes
Section 31 Assessment
1 Describe the characteristics that identify a sampleof matter as being a substance
2 Classify each of the following as a physical orchemical property
a Iron and oxygen form rustb Iron is more dense than aluminumc Magnesium burns brightly when ignitedd Oil and water do not mixe Mercury melts at 39degC
3 Create a table that describes the three commonstates of matter in terms of their shape volumeand compressibility
4 Thinking Critically Using what you know aboutthe compressibility of gases explain why the oxy-gen in a SCUBA tank is compressed
5 Interpreting Data Bromine is a reddish-brownliquid that boils at 59degC Bromine is highly reactivewith many metals For example it reacts withsodium to form a white solid Classify each of theseproperties of bromine as either a physical or achemical property
problem-solving LAB
How is compressed gasreleasedRecognizing Cause and Effect Tanks of com-pressed gases are a common sight in a chemistrylaboratory For example nitrogen is often flowedover a reaction in progress to displace othergases that might interfere with the experimentGiven what you know about the properties ofgases explain how compressed nitrogen isreleased
AnalysisBy definition the particles of gases are far apartand gases tend to fill their container even if thecontainer is a laboratory room Tanks of com-pressed gas come from the supplier capped toprevent the gas from escaping In the lab achemist or technician attaches a regulator to thetank and secures the tank to a stable fixture
Thinking Critically1 Explain why the flow of compressed gas must
be controlled for practical use
2 Predict what would happen if the valve on afull tank of compressed gas were suddenlyopened all the way or if the full tank werepunctured
The fact that substances can change form as in the example of waterchanging to steam is another important concept in chemistry If you reviewwhat you just learned about physical properties of substances you can seethat because the particular form of a substance is a physical property chang-ing the form introduces or adds another physical property to its list of char-acteristics In fact resources that provide tables of physical and chemicalproperties of substances such as the CRC Handbook of Chemistry and Physicsgenerally include the physical properties of substances in all of the states inwhich they can exist
chemistrymccomself_check_quiz
null
38870155
32 Changes in Matter 61
Objectivesbull Define physical change and
list several common physicalchanges
bull Define chemical change andlist several indications that achemical change has takenplace
bull Apply the law of conserva-tion of mass to chemicalreactions
Vocabularyphysical changechemical changelaw of conservation of mass
Section Changes in Matter
You learned in Section 31 that scientists can describe matter in terms of phys-ical and chemical properties For example a physical property of copperallows it to be drawn into copper wire and a chemical property of copperaccounts for the fact that when a solution of copper ions is combined withammonia the copper solution changes to a deep blue color The key conceptin both of these examples is that the substance copper changed in some wayIn this section yoursquoll explore how matter changes as a result of its physicaland chemical properties
Physical ChangesA substance often undergoes changes that result in a dramatically differentappearance yet leave the composition of the substance unchanged An exam-ple is the crumpling of a sheet of aluminum foil While the foil goes from asmooth flat mirrorlike sheet to a round compact ball the actual composi-tion of the foil is unchangedmdashit is still aluminum Changes such as this whichalter a substance without changing its composition are known as physicalchanges Cutting a sheet of paper and breaking a crystal are other examplesof physical changes in matter Can you name some other physical changesYour list might include verbs such as bend grind crumple split and crushall of which indicate physical change
As with other physical properties the state of matter depends on the tem-perature and pressure of the surroundings As temperature and pressurechange most substances undergo a change from one state (or phase) toanother For example at atmospheric pressure and at temperatures below0degC water is in its solid state which is known as ice As heat is added to theice it melts and becomes liquid water This change of state is a physicalchange because even though ice and water have very different appearancestheir composition is the same If the temperature of the water increases to100degC the water begins to boil and liquid water is converted to steam Meltingand formation of a gas are both physical changes and phase changes Figure3-7 shows condensation another common phase change When you encounterterms such as boil freeze condense vaporize or melt in your study of chem-istry the meaning generally refers to a phase change in matter
32
a
Figure 3-7
Condensation on an icy bev-erage glass is the result of thephase change of water ina gaseous state to water in aliquid state
The characteristic ldquofogrdquo ofdry ice is actually fine waterdroplets formed by condensa-tion of water vapor from the airsurrounding the very cold dryice Refer to Table C-1 inAppendix C for a key to atomcolor conventions
b
a
b
a b
LAB
See page 953 in Appendix E forComparing Frozen Liquids
null
15443536
null
4174369
The temperature and pressure at which a substance undergoes a phasechange are important physical properties These properties are listed as themelting and boiling points of the substance Table 3-1 on page 56 providesthis information for several common substances Like density the meltingpoint and boiling point are intensive physical properties that may be used toidentify unknown substances For example if an unknown solid melts at801degC and boils at 1413degCmdashvery high temperaturesmdashit is most probablysodium chloride or common table salt Tables of intensive properties suchas those given in the CRC Handbook of Chemistry and Physics are indis-pensable tools in identifying unknown substances from experimental data
Chemical ChangesAs you learned earlier chemical properties relate to the ability of a substanceto combine with or change into one or more substances A process thatinvolves one or more substances changing into new substances is called achemical change which is commonly referred to as a chemical reaction Thenew substances formed in the reaction have different compositions and dif-ferent properties from the substances present before the reaction occurred Forexample the crushing of grapes that is part of the wine-making process is aphysical change but the fermentation of the juice sugars and other ingredi-ents to wine is a chemical change The Chemistry and Society feature at theend of the chapter describes some interesting consequences of physical andchemical changes in the production of concrete
Letrsquos consider again the rusting of iron When a freshly exposed iron surface is left in contact with air it slowly changes into a new substancenamely the rust shown in Figure 3-8a The iron reacts with oxygen in the airto form a new substance rust Rust is a chemical combination of iron and oxy-gen In chemical reactions the starting substances are called reactants and thenew substances that are formed are called products Thus iron and oxygen arereactants and rust is a product When you encounter terms such as exploderust oxidize corrode tarnish ferment burn or rot the meaning generallyrefers to a chemical reaction in which reactant substances produce differentproduct substances
62 Chapter 3 MattermdashProperties and Changes
a
Figure 3-8
The formation of a gas orsolid when reactants mix oftenindicates that a chemical reac-tion has taken place Rust is theresult of a chemical reaction
Color changes generallyindicate that a chemical reactionhas taken place One example isthe color change of tree leavesin the fall
b
a
b
null
14978511
Evidence of a chemical reaction As Figure 3-8a shows rust is a brown-ish-orange powdery substance that looks very different from iron and oxygenRust is not attracted to a magnet whereas iron is The observation that the prod-uct (rust) has different properties than the reactants (iron and oxygen) is evi-dence that a chemical reaction has taken place A chemical reaction alwaysproduces a change in properties Figures 3-8 and 3-9 illustrate several com-mon indicators of chemical change The CHEMLAB at the end of the chap-ter provides a practical laboratory experience with chemical reactions
Conservation of MassAlthough chemical reactions have been observed over the course of humanhistory it was only in the late eighteenth century that scientists began to usequantitative tools to monitor chemical changes The revolutionary quantita-tive tool developed at this time was the analytical balance which was capa-ble of measuring very small changes in mass
By carefully measuring mass before and after many chemical reactions itwas observed that although chemical changes occurred the total massinvolved in the reaction remained constant The constancy of mass in chem-ical reactions was observed so often that scientists assumed the phenomenonmust be true for all reactions They summarized this observation in a scien-tific law The law of conservation of mass states that mass is neither creatednor destroyed during a chemical reactionmdashit is conserved This law was oneof the great achievements of eighteenth-century science The equation formof the law of conservation of mass is
Massreactants Massproducts
The French scientist Antoine Lavoisier (1743ndash1794) was one of the firstto use an analytical balance like the one shown in Figure 3-10 to monitorchemical reactions He studied the thermal decomposition of mercury(II)oxide known then as calx of mercury Mercury(II) oxide is a powderyred solid When it is heated the red solid reacts to form silvery liquidmercury and colorless oxygen gas as shown in Figure 3-11 on the nextpage The color change and production of a gas are indicators of a
32 Changes in Matter 63
Figure 3-9
Energy changes indicatechemical reactions For examplethe burning of wood is a com-mon example of a reaction thatreleases heat
The change in the smell of asubstance or the production ofan odor may be an indication ofa chemical reaction
b
a
a b
Figure 3-10
The development of scientifictools such as this analytical bal-ance gave a degree of precisionto measurements that greatlyimproved general scientificunderstanding
null
1447691
64 Chapter 3 MattermdashProperties and Changes
chemical reaction When the reaction is performed in a closed container theoxygen gas cannot escape and the mass before and after the reaction can bemeasured The masses will be the same
Mercury(II) oxide yields mercury oxygen2 HgO rarr 2 Hg + O2
A more modern digital analytical balance can be used to prove the conser-vation of mass of this example The law of conservation of mass is one of themost fundamental concepts of chemistry Letrsquos examine more closely somesituations that illustrate the concept Example Problem 3-1 leads you througha sample calculation The practice problems also illustrate the law of con-servation of mass
200 g 16 gmass of products
216 gMass of reactant
EXAMPLE PROBLEM 3-1
Mercury occurs naturally in airwater soil and living organismsSeafood that is intended forhuman consumption is monitoredto ensure that the products donot contain levels of mercuryexceeding the established limitsfor public safety
Figure 3-11
Lavoisierrsquos experimental decom-position of mercury(II) oxide isone proof of the law of conser-vation of mass Although achemical reaction is obvious(powder to liquid mercury) mat-ter was neither created nordestroyed
Conservation of MassIn an experiment 1000 g of red mercury(II) oxide powder is placedin an open flask and heated until it is converted to liquid mercuryand oxygen gas The liquid mercury has a mass of 926 g What isthe mass of oxygen formed in the reaction
1 Analyze the ProblemYou are given the mass of a reactant and the mass of one of theproducts in a chemical reaction Applying the law of conserva-tion of mass the total mass of the products must equal the totalmass of the reactants This means that the mass of the liquidmercury plus the mass of the oxygen gas must equal the mass ofthe mercury(II) oxide powder
Known Unknown
Mass of mercury(II) oxide Mass of oxygen formed 1000 g gMass of liquid mercury 926 g
null
4346781
32 Changes in Matter 65
PRACTICE PROBLEMS6 From a laboratory process designed to separate water into hydrogen
and oxygen gas a student collected 100 g of hydrogen and 794 g ofoxygen How much water was originally involved in the process
7 A student carefully placed 156 g of sodium in a reactor supplied withan excess quantity of chlorine gas When the reaction was completethe student obtained 397 g of sodium chloride How many grams ofchlorine gas reacted How many grams of sodium reacted
8 In a flask 103 g of aluminum reacted with 1000 g of liquid bromineto form aluminum bromide After the reaction no aluminumremained and 85 grams of bromine remained unreacted How manygrams of bromine reacted How many grams of compound wereformed
9 A 100-g sample of magnesium reacts with oxygen to form 166 g ofmagnesium oxide How many grams of oxygen reacted
Section 32 Assessment
10 Describe the results of a physical change and listthree examples of physical change
11 Describe the results of a chemical change Listfour indicators of chemical change
12 Solve each of the following
a In the complete reaction of 2299 g of sodiumwith 3545 g of chlorine what mass of sodiumchloride is formed
b A 122-g sample of X reacts with a sample ofY to form 789 g of XY What is the mass of Ythat reacted
13 Thinking Critically A friend tells you ldquoBecausecomposition does not change during a physicalchange the appearance of a substance does notchangerdquo Is your friend correct Explain why
14 Classifying Classify each of the following ex-amples as a physical change or a chemical change
a crushing an aluminum canb recycling used aluminum cans to make new
aluminum cansc aluminum combining with oxygen to form alu-
minum oxide
For more practice withconservation of massgo to SupplementalPractice Problems in
Appendix A
Practice
2 Solve for the UnknownWrite an equation showing conservation of mass of reactants andproducts
Massreactants Massproducts
Massmercury(II) oxide Massmercury Massoxygen
Solve the equation for Massoxygen
Massoxygen Massmercury(II) oxide Massmercury
Substitute known values and solve
Massoxygen 1000 g 926 g
Massoxygen 074 g
3 Evaluate the AnswerThe sum of the masses of the two products equals the mass of thereactant verifying that mass has been conserved The answer is cor-rectly expressed to the hundredths place
chemistrymccomself_check_quiz
66 Chapter 3 MattermdashProperties and Changes
Section 33 Mixtures of Matter
Objectivesbull Contrast mixtures and
substances
bull Classify mixtures as homo-geneous or heterogeneous
bull List and describe severaltechniques used to separatemixtures
Vocabularymixtureheterogeneous mixturehomogeneous mixturesolutionfiltrationdistillationcrystallizationchromatography
When scientists speak of the composition of matter they are referring to thekinds and amounts of components of which the matter is made On the basisof composition alone all matter can be classified into two broad categoriessubstances or mixtures You have already learned that a pure substance is aform of matter with a uniform and unchanging composition You also knowthat the intensive properties of pure substances do not change regardless ofthe physical state or amount of the substance But what is the result when twoor more substances are combined
MixturesA mixture is a combination of two or more pure substances in which eachpure substance retains its individual chemical properties The composition ofmixtures is variable and the number of mixtures that can be created by com-bining substances is infinite Although much of the focus of chemistry is thebehavior of substances it is important to remember that most everyday mat-ter occurs as mixtures Substances tend naturally to mix it is difficult to keepthings pure
Two mixtures sand and water and table salt and water are shown inFigure 3-12a You know water to be a colorless liquid Sand is a grainy solidthat does not dissolve in water When sand and water are mixed the twosubstances are in contact yet each substance retains its properties Thesand and water have not reacted Just by looking at the sandndashwater mixturein beaker A it is easy to see each separate substance Some mixtures how-ever may not look like mixtures at all The mixture of table salt and waterin the beaker labeled B is colorless and appears the same as pure water Howcan you determine if it is a mixture If you were to boil away the wateryou would see a white residue That residue shown in Figure 13-12b isthe salt Thus the colorless mixture actually contained two separate sub-stances The salt and the water physically mixed but did not react and wereseparated by the physical method of boiling
Figure 3-12
The components of the sandand water mixture (left) areobvious whereas the compo-nents of the table salt and watermixture (right) are not
The salt component becomesobvious when the mixture isboiled
b
a
a b
null
14105936
null
3108555
Types of mixtures The combinations of pure substances shown inFigure 3-12 are indeed both mixtures despite their obvious visual differencesCan you think of some way to further define mixtures Mixtures themselvesare classified as either heterogeneous or homogeneous A heterogeneousmixture is one that does not blend smoothly throughout and in which the indi-vidual substances remain distinct The sand and water mixture is an exampleof a heterogeneous mixture Suppose you draw a drop from the top of the mix-ture using an eyedropper The drop would be almost completely water If youdraw a second drop from the bottom of the mixture that drop would containmostly sand Thus the composition of the sandndashwater mixture is not uniformmdashthe substances have not blended smoothly and the two substances of the mix-ture (sand on the bottom and water on the top) remain distinct In anotherexample fresh-squeezed orange juice is a mixture of juice and pulp The pulpcomponent floats on top of the juice component Is your favorite pizza a mix-ture The answer is yes when you consider that the pizza is a combination ofdistinct areas of dough sauce cheese and toppings We can therefore say thatthe existence of two or more distinct areas indicates a heterogeneous mixture
A homogeneous mixture has constant composition throughout it alwayshas a single phase Letrsquos examine the saltndashwater mixture using the eyedrop-per A drop of the mixture from the top of the beaker has the same composi-tion as a drop from the bottom of the beaker In fact every drop of the mixturecontains the same relative amounts of salt and water
Homogeneous mixtures are also referred to as solutions You are proba-bly most familiar with solutions in a liquid form such as cough suppressantmedicine and lemonade but solutions may contain solids liquids or gasesTable 3-3 lists the various types of solution systems and gives an example ofeach Solutions are very important in chemistry and in fact this textbookdevotes an entire chapter to the study of solutions
The solidndashsolid solution known as steel is called an alloy An alloy is ahomogeneous mixture of metals or a mixture of a metal and a nonmetal inwhich the metal substance is the major component The US Mintrsquos goldendollar coin shown in Figure 3-13 uses a metal alloy composed of 77 cop-per 12 zinc 7 manganese and 4 nickel surrounding a copper coreAlloys are also used in spacecraft and automobiles What might be the ben-efit of using alloys for these applications Manufacturers combine the prop-erties of various metals in an alloy to achieve greater strength and durabilityof their products
33 Mixtures of Matter 67
Types of Solution Systems
System Example
Gasndashgas Air is primarily a mixture of nitrogen oxygen and argongases
Gasndashliquid Carbonated beverages contain carbon dioxide gas in solution
Liquidndashgas Moist air contains water droplets in air (which is a mixture ofgases)
Liquidndashliquid Vinegar contains acetic acid in water
Solidndashliquid Sweetened powder drink contains sugar and other solidingredients in water
Solidndashsolid Steel is an alloy of iron containing carbon
Table 3-3
Figure 3-13
Coins issued by the US Mint are metal alloys The combina-tion of multiple metals gives thecoins specific properties such ascolor weight and durability
null
17554436
Separating MixturesMost matter exists naturally as mixtures For students and scientists to gain athorough understanding of matter it is very important to be able to do the reverseof mixing that is to separate mixtures into their component substances Becausethe substances in a mixture are physically combined the processes used to sep-arate a mixture are physical processes that are based on the difference in phys-ical properties of the substances Sometimes it is very easy to separate a mixtureseparating a mixture of pennies and nickels is not a difficult task More difficultwould be separating a mixture of sand and iron filings Or would it be Thedemonstration illustrated in Figure 3-14 shows how the sandndashiron mixture iseasily separated on the basis of the unique physical properties of the substancesinvolved Numerous techniques have been developed that take advantage of dif-ferent physical properties in order to separate mixtures
Heterogeneous mixtures composed of solids and liquids are easily separatedby filtration Filtration is a technique that uses a porous barrier to separate asolid from a liquid As Figure 3-15 shows the mixture is poured through apiece of filter paper that has been folded into a cone shape The liquid passesthrough leaving the solids trapped in the filter paper
68 Chapter 3 MattermdashProperties and Changes
Figure 3-14
The physical properties of theiron filings on the plate allowthem to be easily separatedfrom the sand using a magnet
Separating Ink DyesApplying Concepts Chromatography is animportant diagnostic tool for chemists Manytypes of substances can be separated and ana-lyzed using this technique In this experiment youwill use paper chromatography to separate thedyes in water-soluble black ink
Materials 9-oz wide-mouth plastic cups (2)round filter paper 1frasl4 piece of 11-cm round filterpaper scissors pointed object approximately 3ndash4mm diameter water-soluble black felt pen ormarker
Procedure 1 Fill one of the wide-mouth plastic cups with
water to about 2 cm from the top Wipe offany water drops on the lip of the cup
2 Place the round filter paper on a clean drysurface Make a concentrated ink spot in thecenter of the paper by firmly pressing the tipof the pen or marker onto the paper
3 Use a sharp object to create a small holeapproximately 3ndash4 mm or about the diameterof a pen tip in the center of the ink spot
4 Roll the 14 piece of filter paper into a tightcone This will act as a wick to draw the inkWork the pointed end of the wick into thehole in the center of the round filter paper
5 Place the paperwick apparatus on top of thecup of water with the wick in the water The
water will move up the wick and outwardthrough the round paper
6 When the water has moved to within about1 cm of the edge of the paper (about 20 min-utes) carefully remove the paper from thewater-filled cup and put it on the empty cup
Analysis1 Make a drawing of the round filter paper and
label the color bands How many distinct dyescan you identify
2 Why do you see different colors at differentlocations on the filter paper
3 How does your chromatogram compare withthose of your classmates who used other typesof black felt pens or markers Explain the differences
miniLAB
null
7988226
Most homogeneous mixtures can be separated by distillation Distillationis a separation technique that is based on differences in the boiling points ofthe substances involved In distillation a mixture is heated until the substancewith the lowest boiling point boils to a vapor that can then be condensed intoa liquid and collected When precisely controlled distillation can separate sub-stances having boiling points that differ by only a few degrees
Did you ever make rock candy as a child Making rock candy from a sugarsolution is an example of separation by crystallization Crystallization is a sep-aration technique that results in the formation of pure solid particles of a sub-stance from a solution containing the dissolved substance When the solutioncontains as much dissolved substance as it can possibly hold the addition ofa tiny amount more often causes the dissolved substance to come out of solu-tion and collect as crystals on some available surface In the rock candy exam-ple as water evaporates from the sugarndashwater solution the sugar is left behindas a solid crystal on the string Crystallization produces highly pure solids
Chromatography is a technique that separates the components of a mix-ture (called the mobile phase) on the basis of the tendency of each to travelor be drawn across the surface of another material (called the stationaryphase) The miniLAB in this section describes how you can separate a solu-tion such as ink into its components as it spreads across a stationary piece ofpaper The separation occurs because the various components of the inkspread through the paper at different rates
33 Mixtures of Matter 69
Figure 3-15
Filtration is a common techniqueused to remove impurities fromdrinking water Clean waterpasses through the porous filter
leaving behind the impuritiesthat can be easily discarded ba
Section 33 Assessment
15 How do mixtures and substances differ
16 Consider a mixture of water sand and oil Howmany phases are present How could you separatethis mixture into individual substances
17 Classify each of the following as either a hetero-geneous or homogeneous mixture
a orange juiceb tap waterc steel (a blend of iron and carbon)d aire raisin muffin
18 Thinking Critically When 50 mL of ethanol ismixed with 50 mL of water a solution forms Thevolume of the final solution is less than 100 mLPropose an explanation for this phenomenon(Hint Consider what you know about the spacebetween particles in liquids)
19 Applying Concepts Describe the separationtechnique that could be used to separate each ofthe following mixtures
a two colorless liquidsb a nondissolving solid mixed with a liquidc red and blue marbles of same size and mass
a b
chemistrymccomself_check_quiz
Topic MixturesTo learn more about mixturesand separation techniquesvisit the Chemistry Web siteat chemistrymccomActivity Use your research tomake a poster showing sev-eral real-life mixtures theiruses and techniques thatmight be used to separateeach mixture
null
10365246
70 Chapter 3 MattermdashProperties and Changes
Section 34 Elements and Compounds
Objectivesbull Distinguish between ele-
ments and compounds
bull Describe the organizationof elements on the periodictable
bull Explain how all compoundsobey the laws of definiteand multiple proportions
Vocabularyelementperiodic tablecompoundlaw of definite proportionspercent by masslaw of multiple proportions
To this point yoursquove examined many of the properties of matter Yoursquove alsolearned how scientists have organized classified and described matter byarranging it into various subcategories of components But there remainsanother fundamental level of classification of matter the classification of puresubstances as elements or compounds
ElementsRecall that earlier in this chapter you considered the diversity of your sur-roundings in terms of matter Although the diversity is astounding in realityall matter can be broken down into a relatively small number of basic build-ing blocks called elements An element is a pure substance that cannot beseparated into simpler substances by physical or chemical means On Earth91 elements occur naturally Copper oxygen and gold are examples of nat-urally occurring elements There are also several elements that do not existnaturally but have been developed by scientists
Each element has a unique chemical name and symbol The chemical sym-bol consists of one two or three letters the first letter is always capitalizedand the remaining letter(s) are always lowercase Why has so much effort beengiven to naming the elements The names and symbols of the elements areuniversally accepted by scientists in order to make the communication ofchemical information possible
The 91 naturally occurring elements are not equally abundant For exam-ple hydrogen is estimated to make up approximately 75 of the mass of theuniverse Oxygen and silicon together comprise almost 75 of the mass ofEarthrsquos crust while oxygen carbon and hydrogen account for more than 90of the human body Francium on the other hand is one of the least abundantnaturally occurring elements It is estimated that there is probably less than20 grams of francium dispersed throughout Earthrsquos crust To put that into per-spective the total mass of francium is approximately equal to the mass of yourpencil or pen
A first look at the periodic table As many new elements werebeing discovered in the early nineteenth century chemists began to seepatterns of similarities in the chemical and physical properties of par-ticular sets of elements Several schemes for organizing the elementson the basis of these similarities were proposed with varying degreesof success In 1869 the Russian chemist Dmitri Mendeleev made asignificant contribution to the effort Mendeleev devised the chartshown in Figure 3-16 which organized all of the elements that wereknown at the time into rows and columns based on their similaritiesand their masses Mendeleevrsquos organizational table was the first ver-sion of what has been further developed into the periodic table of ele-ments The periodic table organizes the elements into a grid ofhorizontal rows called periods and vertical columns called groups orfamilies Elements in the same group have similar chemical and phys-ical properties The table is called ldquoperiodicrdquo because the pattern ofsimilar properties repeats as you move from period to period
One of the brilliant aspects of Mendeleevrsquos original table was thatits structure could accommodate elements that were not known at
Figure 3-16
Although many early scientistshave contributed to the modernorganization of the elementsMendeleevrsquos system of rows andcolumns was a revolutionaryadvancement
null
20846185
null
10260762
Heterogeneousmixtures
dirt bloodmilk
lemonade gasolinesteel
oxygen goldiron
salt baking sodasugar
Homogeneousmixtures Elements Compounds
Matter
Mixtures
Physicalchanges
Chemicalchanges
Pure substances
the time Notice the blank spots in Mendeleevrsquos table By analyzing the sim-ilarities among the elements and their pattern of repetition Mendeleev wasable to predict the properties of elements that were yet to be discovered
In most cases Mendeleevrsquos predictions (and the blanks in the table)closely matched the characteristics of new elements as they were discoveredFigure 3-18 on pages 72ndash73 shows samples of the elements in their arrange-ment in the periodic table The standard modern version of the periodic tableincludes more than 100 elements Yoursquoll study the periodic table in greaterdetail later in this textbook In fact the periodic table remains a dynamic toolas scientists continue to discover new elements
CompoundsTake a moment to recall what you have learned about the organization of mat-ter using Figure 3-17 as a guide You know that matter is classified as puresubstances and mixtures As you learned in the previous section mixtures canbe homogeneous or heterogeneous You also know that elements are pure sub-stances that cannot be separated into simpler substances There is yet anotherclassification of pure substancesmdashcompounds A compound is a combina-tion of two or more different elements that are combined chemically Mostof the substances that you are familiar with and in fact much of the matterof the universe are compounds Water table salt table sugar and aspirin areexamples of common compounds
Today there are approximately 10 million known compounds and newcompounds continue to be developed and discovered at the rate of about100 000 per year Can you recall some of the medicinal compounds that havemade headlines in recent years There appears to be no limit to the numberof compounds that can be made or that will be discovered Considering thisvirtually limitless potential several organizations have assumed the task ofcollecting data and indexing the known chemical compounds These organi-zations maintain huge databases that allow researchers to access informationon existing compounds The databases and retrieval tools enable scientists tobuild the body of chemical knowledge in an efficient manner
The chemical symbols of the periodic table make it easy to write the for-mulas for chemical compounds For example table salt or sodium chlorideis composed of one part sodium (Na) and one part chlorine (Cl) and its chem-ical formula is NaCl Water is composed of two parts hydrogen (H) to one partoxygen (O) and its formula is H2O
34 Elements and Compounds 71
Figure 3-17
The concept of matter is far-reaching and can be overwhelm-ing But when broken down asshown here it becomes clearhow elements compounds sub-stances and mixtures define allmatter
null
16906535
72 Chapter 3 MattermdashProperties and Changes
IA1
IIA2
IIIB IVB VB VIB VIIB VIII3 4 5 6 7 8 9
101 H
693 Li
23011 Na 243
12 Mg
39119 K
85537 Rb
132955 Cs
22387 Fr
22789 Ac
138957 La
23290 Th
140158 Ce
23191 Pa
140959 Pr
23892 U
144260 Nd
23793 Np
14561 Pm
904 Be
40120 Ca
87638 Sr
137356 Ba
22688 Ra
45021 Sc
88939 Y
138957 La
22789 Ac
47922 Ti
91240 Zr
178572 Hf
261104 Rf
50923 V
92941 Nb
180973 Ta
262105 Db
52024 Cr
95942 Mo
183874 W
266106 Sg
54925 Mn
9843 Tc
186275 Re
264107 Bh
55826 Fe
101144 Ru
190276 Os
269108 Hs
58927 Co
102945 Rh
192277 Ir
268109 Mt
22 min 1600 a 22 a 65 s 34 s 21 s 440 ms
42middot106a
21middot106a14middot1010a 33middot104a 45middot109a22 a
18 a
93 s 70 ms
11
22
33
44
55
66
77
Periodic Table
Figure 3-18
The periodic table shown aboveillustrates samples of many ofthe elements Be sure to use theperiodic table on pages 156-157for reference throughout yourchemistry course
34 Elements and Compounds 73
VIIIA18
IB IIB10 11 12
IIIA IVA VA VIA VIIA13 14 15 16 17
24494 Pu
150462 Sm
24395 Am
152063 Eu
24796 Cm
157364 Gd
24797 Bk
158965 Tb
25198 Cf
162566 Dy
25299 Es
164967 Ho
257100 Fm
167368 Er
258101 Md
168969 Tm
259102 No
173070 Yb
262103 Lr
175071 Lu
58728 Ni
106446 Pd
195178 Pt
273110
63529 Cu
107947 Ag
197079 Au
272111
65430 Zn
112448 Cd
200680 Hg
69731 Ga
114849 In
204481 Tl
72632 Ge
118750 Sn
207282 Pb
74933 As
121851 Sb
209083 Bi
79034 Se
127652 Te
20984 Po
79935 Br
126953 I
21085 At
83836 Kr
27013 Al 281
14 Si 31015 P 321
16 S 35517 Cl 399
18 Ar
1085 B 120
6 C 1407 N 160
8 O 1909 F 202
10 Ne
402 He
131354 Xe
22286 Rn
277112
102 a 81 h
16middot107a80middot107a 7400 a 1400 a 900 a 472 d 101 d 52 d 58 min 36 h
38 d
118 ms 15 ms 024 ms
of the Elements
Unlike elements compounds can be broken down into simpler substancesby chemical means In general compounds that naturally occur are more sta-ble than the individual component elements To separate a compound into itselements often requires external energy such as heat or electricity Figure 3-19shows the apparatus used to produce the chemical change of water into its com-ponent elements of hydrogen and oxygen through a process called electrolysisHere one end of a long platinum electrode is exposed to the water in the tubeand the other end is attached to a power source An electric current splits waterinto hydrogen gas in the compartment on the right and oxygen gas in the com-partment on the left Because water is composed of two parts hydrogen and onepart oxygen there is twice as much hydrogen gas than oxygen gas
The properties of a compound are different from those of its componentelements The example of water in Figure 3-19 illustrates this fact Water isa stable compound that is liquid at room temperature When water is broken
down into its components it is obvious that hydro-gen and oxygen are dramatically different than theliquid they form when combined Oxygen andhydrogen are tasteless odorless gases that vigor-ously undergo chemical reactions with many ele-ments This difference in properties is a result of achemical reaction between the elements Figure 3-20 shows the component elements (sodium andchlorine) of the compound commonly called tablesalt (sodium chloride) When sodium and chlorinereact with each other the compound sodium chlo-ride is formed Note how different the properties ofsodium chloride are from its component elementsSodium is a highly reactive element that fizzes andburns when added to water Chlorine is a poison-ous pale green gas Sodium chloride however isa white unreactive solid that flavors many of thefoods you eat
74 Chapter 3 MattermdashProperties and Changes
Figure 3-19
This classic apparatus called aHoffman apparatus and othersimilar designs are used to sepa-rate water into its components
Figure 3-20
Compounds such as sodium chlo-ride (table salt) are oftenremarkably different from thecomponents that comprise them
Sodium
Chlorine
Sodiumchloride
null
11723543
Law of Definite ProportionsAn important characteristic of compounds is that the elements comprisingthem combine in definite proportions by mass This observation is so funda-mental that it is summarized as the law of definite proportions This lawstates that regardless of the amount a compound is always composed of thesame elements in the same proportion by mass For example consider thecompound table sugar (sucrose) which is composed of carbon hydrogen andoxygen The analysis of 2000 g of sucrose from a bag of sugar is given inTable 3-4 Note that in Column 1 the sum of the individual masses of the ele-ments equals 2000 g the amount of sucrose that was analyzed This demon-strates the law of conservation of mass as applied to compounds The massof the compound is equal to the sum of the masses of the elements that makeup the compound Column 2 shows the ratio of the mass of each element tothe total mass of the compound as a percentage called the percent by mass
percent by mass () mmas
asss
ofof
coemlem
poeunntd 100
Now letrsquos suppose you analyzed 5000 g of sucrose isolated from a sampleof sugar cane The analysis is shown in Table 3-5 Note in Column 2 thatthe percent by mass values equal those in Column 2 in Table 3-4 Accordingto the law of definite proportions samples of a compound from any sourcemust have the same mass proportions Conversely compounds with differentmass proportions must be different compounds Thus you can conclude thatsamples of sucrose always will be composed of 422 carbon 650 hydro-gen and 5130 oxygen
34 Elements and Compounds 75
Sucrose Analysis from Bag Sugar
Column 1 Column 2
Element Analysis by mass (g) Percent by mass ()
Carbon 844 g carbon 100 422 carbon
Hydrogen 130 g hydrogen 100 650 hydrogen
Oxygen 1026 g oxygen 100 5130 oxygen
Total 2000 g sucrose 1000
Table 3-4
Sucrose Analysis from Sugar Cane
Column 1 Column 2
Element Analysis by mass (g) Percent by mass ()
Carbon 2110 g carbon 100 4220 carbon
Hydrogen 325 g hydrogen 100 650 hydrogen
Oxygen 2565 g oxygen 100 5130 oxygen
Total 5000 g sucrose 10000
Table 3-5
200804
g4
sguc
Crose
200103
g0
sguc
Hrose
2010002g6sguc
Orose
5002101g0
sugcCrose
500302
g5
sguc
Hrose
5002506g5
sguc
Orose
HistoryCONNECTION
Antoine-Laurent Lavoisier(1743ndash1794) is recognized as
the father of modern chemistryWhile his fellow scientists tried toexplain matter based on the ele-ments fire earth air and waterLavoisier performed some of thefirst quantitative chemical experi-ments His data and observationsled to the statement of the lawof conservation of mass He alsostudied the nature of combustionand devised a system of namingelements
Lavoisier is credited withdetermining that water resultsfrom the combination of the ele-ments oxygen and hydrogen Healso studied respiration in ani-mals and plants and defined therole of oxygen in the process ofrespiration He determined thathumans take in oxygen and giveoff carbon dioxide during respira-tion
Lavoisier wrote several booksincluding Treatise on ChemicalElements 1789 in which he fur-ther defined the nature of ele-ments and Method of ChemicalNomenclature 1787 describinghis idea for a chemical namingsystem which eventally served asthe basis for the naming systemof modern chemistry
null
10861547
76 Chapter 3 MattermdashProperties and Changes
PRACTICE PROBLEMS20 A 780-g sample of an unknown compound contains 124 g of hydro-
gen What is the percent by mass of hydrogen in the compound
21 If 10 g of hydrogen reacts completely with 190 g of fluorine what isthe percent by mass of hydrogen in the compound that is formed
22 If 35 g of X reacts with 105 g of Y to form the compound XY what isthe percent by mass of X in the compound The percent by mass of Y
23 Two unknown compounds are tested Compound I contains 150 g ofhydrogen and 1200 g of oxygen Compound II contains 20 g ofhydrogen and 320 g of oxygen Are the compounds the same
24 All you know about two unknown compounds is that they have thesame percent by mass of carbon With only this information can yoube sure the two compounds are the same
Law of Multiple ProportionsCompounds composed of different elements are obviously different com-pounds Can compounds that are composed of the same elements differ fromeach other The answer is yes because those different compounds have dif-ferent mass compositions The law of multiple proportions states that whendifferent compounds are formed by a combination of the same elements dif-ferent masses of one element combine with the same relative mass of the otherelement in a ratio of small whole numbers Ratios compare the relativeamounts of any items or substances The comparison can be expressed usingnumbers separated by a colon or as a fraction With regard to the law of mul-tiple proportions ratios express the relationship of elements in a compound
The two distinct compounds water (H2O) and hydrogen peroxide (H2O2)illustrate the law of multiple proportions Each compound contains the sameelements (hydrogen and oxygen) Water is composed of two parts hydrogen(the element that is present in the same amount in both compounds) to onepart oxygen (the element that is present in different amounts in both com-pounds) Hydrogen peroxide is composed of two parts hydrogen and two partsoxygen Hydrogen peroxide differs from water in that it has twice as muchoxygen When we compare the mass of oxygen in hydrogen peroxide to themass of oxygen in water we get the ratio 21
In another example copper (Cu) reacts with chlorine (Cl) under differentsets of conditions to form two different compounds Table 3-6 provides ananalysis of their composition Note that the two copper compounds must bedifferent because they have different percents by mass Compound I contains6420 copper compound II contains 4727 copper Compound I contains3580 chlorine compound II contains 5273 chlorine
Figure 3-21
Bar graph compares the rela-tive masses of copper and chlo-rine in Compound I and bargraph compares the relativemasses of copper and chlorine inCompound II A comparisonbetween the relative masses ofcopper in both compoundsshows a 21 ratio
b
a
Analysis Data of Two Copper Compounds
Mass copper (g) Mass chlorine (g) Mass ratioin 1000 g of in 1000 g of
Compound Cu Cl compound compound mmaassss
CCul
I 6420 3580 6420 3580 1793 g Cu1 g Cl
II 4727 5273 4727 5273 08964 g Cu1 g Cl
Table 3-6
Compound I
Mas
s (g
)
Cu
Cl
1000
2000
Compound II
Mas
s (g
)
Cu Cl
1000
2000
Mass RatioComparison
Mas
s (g
)
1000
2000
II
I
a
b
c
For more practice withpercent by mass andlaw of definite proportions go to
Supplemental PracticeProblemsProblems in Appendix A
Practice
c
null
120996864
Compare the ratio of the mass of copper to the mass of chlorine for eachcompound (see the last column of Table 3-6 and Figure 3-21) Yoursquoll noticethat the mass ratio of copper to chlorine in compound I (1793) is two timesthe mass ratio of copper to chlorine in compound II (08964)
2000
As the law of multiple proportions states the different masses of copper thatcombine with a fixed mass of chlorine in the two different copper com-pounds shown in Figure 3-22 can be expressed as a small whole-numberratio in this case 21
Considering that there is a finite number of elements that exist today andan exponentially greater number of compounds that are composed of theseelements under various conditions it becomes clear how important the lawof multiple proportions is in chemistry
018799634
gg
CCuugg
CCll
mass ratio compound Imass ratio compound II
34 Elements and Compounds 77
Section 34 Assessment
25 How are elements and compounds similar Howare they different
26 What is the basic organizing feature of the peri-odic table of elements
27 Explain how the law of definite proportionsapplies to compounds
28 What type of compounds are compared in the lawof multiple proportions
29 Thinking Critically Name two elements thathave properties similar to those of element potas-sium (K) To those of krypton (Kr)
30 Interpreting Data Complete the following tableand then analyze the data to determine if com-pounds I and II are the same compound If thecompounds are different use the law of multipleproportions to show the relationship between them
Analysis Data of Two Iron Compounds
Compound Total mass (g) Mass Fe (g) Mass O (g) Mass Fe Mass O
I 7500 5246 2254
II 5600 4353 1247
Figure 3-22
Analyses of the mass ratios ofthe two copper chloride com-pounds shown here indicatethat they are indeed differentcompounds The calculated massratio of compound I to com-pound II is 2000 and fits thedefinition of the law of multipleproportions
chemistrymccomself_check_quiz
null
55066444
Pre-Lab
1 Read the entire CHEMLAB
2 Prepare all written materials that you will take intothe laboratory Be sure to include safety precau-tions procedure notes and a data table in which torecord your observations
3 Define the terms physical property and chemicalproperty Give an example of each
4 Form a hypothesis regarding what you mightobserve ifa a chemical change occursb a physical change occurs
5 Distinguish between a homogeneous mixture and aheterogeneous mixture
Procedure
1 Obtain 8 cm of copper wire Rub the copper wirewith the sandpaper until it is shiny
2 Measure approximately 25 mL AgNO3 (silvernitrate) solution into a 50-mL beaker CAUTIONDo not allow to contact skin or clothing
3 Make and record an observation of the physicalproperties of the copper wire and AgNO3solution
78 Chapter 3 MattermdashProperties and Changes
Safety Precautions
bull Always wear safety goggles gloves and lab apronbull Silver nitrate is toxic and will harm skin and clothingbull Use caution around a flame
ProblemIs there evidence of a chemi-cal reaction between copperand silver nitrate If so whichelements reacted and what isthe name of the compoundthey formed
Objectivesbull Observe the reactants as
they change into productbull Separate a mixture by
filtrationbull Predict the names of the
products
Materialscopper wireAgNO3 solutionsandpaperstirring rod50-mL graduated
cylinder50-mL beakerfunnel
filter paper250-mL Erlenmeyer
flaskring standsmall iron ringplastic petri dishpaper clipBunsen burnertongs
Matter and ChemicalReactionsOne of the most interesting characteristics of matter and one that
drives the study and exploration of chemistry is the fact thatmatter changes By examining a dramatic chemical reaction such asthe reaction of the element copper and the compound silver nitratein a water solution you can readily observe chemical changeDrawing on one of the fundamental laboratory techniques intro-duced in this chapter you can separate the products Then you willuse a flame test to confirm the identity of the products
CHEMLAB 3
Reaction Observations
Time(min)
Observations
CHEMLAB 79
4 Coil the piece of copper wire to a length that willfit into the beaker Make a hook on the end of thecoil to allow the coil to be suspended from thestirring rod
5 Hook the coil onto the middle of the stirring rodPlace the stirring rod across the top of the beakerimmersing some of the coil in the AgNO3 solution
6 Make and record observations of the wire and thesolution every five minutes for 20 minutes
7 Use the ring stand small iron ring funnelErlenmeyer flask and filter paper to set up a fil-tration apparatus Attach the iron ring to the ringstand Adjust the height of the ring so the end ofthe funnel is inside the neck of the Erlenmeyerflask
8 To fold the filter paper examine the diagrambelow Begin by folding the circle in half thenfold in half again Tear off the lower right cornerof the flap that is facing you This will help thefilter paper stick better to the funnel Open thefolded paper into a cone Place the filter papercone in the funnel
9 Remove the coil from the beaker and dispose ofit as directed by your teacher Some of the solidproduct may form a mixture with the liquid in thebeaker Decant the liquid by slowly pouring itdown the stirring rod into the funnel Solidproduct will be caught in the filter paper Collectthe filtratemdashthe liquid that runs through the filterpapermdashin the Erlenmeyer flask
10 Transfer the clear filtrate to a petri dish
11 Adjust a Bunsen burner flame until it is blueHold the paper clip with tongs in the flame untilno additional color is observed CAUTION Thepaper clip will be very hot
12 Using tongs dip the hot paper clip in the filtrateThen hold the paper clip in the flame Record thecolor you observe
Cleanup and Disposal
1 Dispose of materials as directed by your teacher
2 Clean and return all lab equipment to its properplace
3 Wash hands thoroughly
Analyze and Conclude
1 Classifying Which type of mixture is silvernitrate in water Which type of mixture is formedin step 6 Explain
2 Observing and Inferring Describe the changesyou observed in step 6 Is there evidence achemical change occurred Why
3 Predicting Predict the products formed in step6 You may not know the exact chemical namebut you should be able to make an intuitiveprediction
4 Using Resources Use resources such as the CRCHandbook of Chemistry and Physics the MerckIndex or the Internet to determine the colors ofsilver metal and copper nitrate in water Comparethis information with your observations of thereactants and products in step 6
5 Identifying Metals emit characteristic colors inflame tests Copper emits blue-green light Doyour observations in step 12 confirm the presenceof copper in the filtrate collected in step 9
6 Communicating Express in words the chemicalequation that represents the reaction that occurredin step 6
7 Compare your recorded obser-vations with those of several other lab teamsExplain any differences
Real-World Chemistry
1 Analytical chemists determine the chemicalcomposition of matter Two major branches ofanalytical chemistry are qualitative analysismdashdetermining what is in a substancemdashand quanti-tative analysismdashmeasuring how much substanceResearch and report on a career as an analyticalchemist in the food industry
Error Analysis
CHAPTER 3 CHEMLAB
Tear corner
Until the Industrial Revolution the amount of car-bon dioxide (CO2) in the atmosphere was fairly con-stant Since the Industrial Revolution however theburning of fossil fuels has contributed to a signifi-cant increase in the amount of carbon dioxide in theatmosphere As the level of carbon dioxide increasesEarth gradually warms up Too much CO2 in theatmosphere can change the conditions on Earth
Another major source of carbon dioxide may bein the foundation of your building or on the side-walks near your school The production of cementthe key ingredient in concrete releases tremendousamounts of carbon dioxide into the atmosphereChemistry may allow engineers to build ldquogreenbuildingsrdquo that are still practical yet have less ofan impact on the environment
Producing CementCement generally begins with a mixture of lime-stone and sand placed in a kiln which heats it toabout 1480degC As the mixture is heated its chem-ical and physical properties change After heatingthe solid that remains is ground into a fine powderThis is cement To make concrete the cement ismixed with fine particles such as sand coarse par-ticles such as crushed stone and water
During the production of cement carbon diox-ide is released in two ways First when the lime-stone is heated it changes into lime and carbondioxide Second the electrical energy used to heatthe kiln is usually supplied by a power plant thatburns fossil fuels such as coal Fossil fuels alsorelease carbon dioxide and other substances
Using FlyashOne way to reduce the amount of carbon dioxidereleased into the atmosphere is to find a replace-ment for cement in concrete One such replacementis a substance known as flyash Flyash is a wasteproduct that accumulates in the smokestacks ofpower plants when ground coal is burned It is afine gray powder that consists of tiny glass beads
Using flyash offers several advantages Flyashordinarily is dumped in landfills Replacing cementwith flyash can reduce CO2 emissions and prevent
tons of waste from piling up in landfills Flyash alsoproduces better concrete Traditional concrete hasweak zones where tiny cracks allow water to flowthrough Flyash contains fine particles that fillspaces and keep moisture out Flyash also protectsthe steel surrounding the concrete makes the con-crete easier to work with and extends the life of theconcrete structure In fact flyash is so reliable theRomans used natural materials similar to flyash tobuild the concrete dome of the Pantheon
Solutions to environmental problems require awilling commitment from scientists architectsbuilders and owners to look for ways to builddurable structures and protect the environment
1 Communicating Ideas Write a pamphlet forpeople who are building new homes tellingthem about the importance of green buildings
2 Using Resources Investigate issues thatinfluence the decision to use flyash Discussthe advantages and disadvantages of flyash
Investigating the Issue
Green Buildings
CHEMISTRY and
Society
80 Chapter 3 MattermdashProperties and Changes
Visit the Chemistry Web site atchemistrymccom to find links to moreinformation about flyash and green buildings
Study Guide 81
CHAPTER STUDY GUIDE3
Vocabulary
Key Equations and Relationships
Summary31 Properties of Matter
bull A substance is a form of matter with a uniform andunchanging composition
bull Physical properties can be observed without alteringa substancersquos composition Chemical propertiesdescribe a substancersquos ability to combine with orchange into one or more new substances
bull Both physical and chemical properties are affected byexternal conditions such as temperature and pressure
bull The three common states of matter are solid liquidand gas
32 Changes in Matterbull A physical change alters the physical properties of a
substance without changing its composition
bull A chemical change also known as a chemical reac-tion involves a change in a substancersquos composition
bull In a chemical reaction reactants form products
bull The law of conservation of mass states that mass isneither created nor destroyed during a chemicalreaction it is conserved
33 Mixtures of Matter
bull A mixture is a physical blend of two or more puresubstances in any proportion
bull Solutions are homogeneous mixtures
bull Mixtures can be separated by physical meansCommon separation techniques include filtrationdistillation crystallization and chromatography
34 Elements and Compoundsbull Elements are substances that cannot be broken down
into simpler substances by chemical or physicalmeans
bull The elements are organized in the periodic table ofelements
bull A compound is a chemical combination of two ormore elements Properties of compounds differ fromthe properties of their component elements
bull The law of definite proportions states that a com-pound is always composed of the same elements inthe same proportions
bull The law of multiple proportions states that if ele-ments form more than one compound those com-pounds will have compositions that are smallwhole-number multiples of each other
bull law of conservation of mass (p 63)Massreactants Massproducts
bull percent by mass MMaasss
c
s
o
e
m
le
p
m
o
e
u
n
n
t
d 100
(p 75)
bull chemical change (p 62)bull chemical property (p 57)bull chromatography (p 69)bull compound (p 71)bull crystallization (p 69)bull distillation (p 69)bull element (p 70)bull extensive properties (p 56)bull filtration (p 68 )bull gas (p 59)
bull heterogeneous mixture (p 67)bull homogeneous mixture (p 67)bull intensive properties (p 56)bull law of conservation of mass
(p 63)bull law of definite proportions
(p 75)bull law of multiple proportions
(p 76)bull liquid (p 58)
bull mixture (p 66)bull percent by mass (p 75)bull periodic table (p 70)bull physical changes (p 61)bull physical property (p 56)bull solid (p 58)bull solution (p 67)bull states of matter (p 58)bull substance (p 55)bull vapor (p 59)
chemistrymccomvocabulary_puzzlemaker
82 Chapter 3 MattermdashProperties and Changes
Go to the Chemistry Web site atchemistrymccom for additionalChapter 3 Assessment
Concept Mapping31 Organize the following terms into a logical concept
map state physical properties virtually incompress-ible solid gas liquid tightly packed particles com-pressible incompressible particles far apart looselypacked particles
Mastering Concepts32 List three examples of substances Explain why each
is a substance (31)
33 List at least three physical properties of tap water (31)
34 Identify each of the following as an extensive or inten-sive physical property (31)
a melting pointb massc densityd length
35 ldquoProperties are not affected by changes in temperatureand pressurerdquo Is this statement true or false Explain(31)
36 Classify each of the following as either solid liquidor gas at room temperature (31)
a milkb airc copperd heliume diamondf candle wax
37 Classify each of the following as a physical propertyor a chemical property (31)
a aluminum has a silvery colorb gold has a density of 19 gcm3
c sodium ignites when dropped in waterd water boils at 100degCe silver tarnishesf mercury is a liquid at room temperature
38 A carton of milk is pouredinto a bowl Describe thechanges that occur in themilkrsquos shape and volume(31)
39 Classify each of the follow-ing as a physical change or a chemical change (32)
a breaking a pencil in twob water freezing and forming icec frying an eggd burning woode leaves turning color in the fall
40 Is a change in phase a physical change or a chemicalchange Explain (32)
41 List four indicators that a chemical change has proba-bly taken place (32)
42 Iron and oxygen combine to form iron oxide (rust)List the reactants and products of this reaction (32)
43 Use Table 3-1 to identify a substance that undergoes aphase change as its temperature increases from 250degCto 210degC What phase change takes place (32)
44 After burning for three hours acandle has lost half of its massExplain why this example doesnot violate the law of conservationof mass (32)
45 Describe the difference between aphysical change and a chemicalchange (32)
46 Describe the characteristics of amixture (33)
47 Describe a method that could be used to separate eachof the following mixtures (33)
a iron filings and sandb sand and saltc the components of inkd helium and oxygen gases
48 ldquoA mixture is the chemical bonding of two or moresubstances in any proportionrdquo Is this statement true orfalse Explain
CHAPTER ASSESSMENTCHAPTER ASSESSMENT3
1
2
4 53
7 86
10 119
chemistrymccomchapter_test
Assessment 83
CHAPTER 3 ASSESSMENT
49 Which of the following are the same and which aredifferent (33)
a a substance and a pure substanceb a heterogeneous mixture and a solutionc a substance and a mixtured a homogeneous mixture and a solution
50 Describe how a homogeneous mixture differs from aheterogeneous mixture (33)
51 A chemistry professor has developed a laboratory taskto give her students practical experience using basicseparation techniques She prepares a liquid solutionof water and another compound Assuming you are astudent in the class name the technique you would useto separate and identify the components Give specificdetails of the method
52 State the definition of an element (34)
53 Name the elements contained in the following compounds (34)
a sodium chloride (NaCl) c ethanol (C2H6O)b ammonia (NH3) d bromine (Br2)
54 How many naturally occurring elements are found onEarth Approximately how many synthetic elementshave been identified (34)
55 What was Dmitri Mendeleevrsquos major contribution tothe field of chemistry (34)
56 Is it possible to distinguish between an element and acompound Explain (34)
57 How are the properties of a compound related to thoseof the elements that comprise it (34)
58 How are the elements contained within a group on theperiodic table related (34)
59 Which law states that a compound always contains thesame elements in the same proportion by mass (34)
Mastering ProblemsProperties of Matter (31)60 A scientist is given the task of identifying an unknown
compound on the basis of its physical properties Thesubstance is a white solid at room temperatureAttempts to determine its boiling point were unsuc-cessful Using Table 3-1 name the unknown com-pound
Conservation of Mass (32)61 A 280-g sample of nitrogen gas combines completely
with 60 g of hydrogen gas to form ammonia What isthe mass of ammonia formed
62 A substance breaks down into its component elementswhen it is heated If 680 grams of the substance ispresent before it is heated what is the combined massof the component elements after heating
63 A 130-g sample of X combines with a 340-g sampleof Y to form the compound XY2 What is the mass ofthe reactants
64 Sodium chloride can be formed by the reaction ofsodium metal and chlorine gas If 4598 g of sodiumcombines with an excess of chlorine gas to form11689 g sodium chloride what mass of chlorine gasis used in the reaction
65 Copper sulfide is formed when copper and sulfur areheated together In this reaction 127 g of copper reactswith 41 g of sulfur After the reaction is complete 9 gof sulfur remains unreacted What is the mass of cop-per sulfide formed
Law of Definite Proportions (34)66 A 253-g sample of an unknown compound contains
08 g of oxygen What is the percent by mass of oxy-gen in the compound
67 Magnesium combines with oxygen to form magne-sium oxide If 1057 g of magnesium reacts com-pletely with 696 g of oxygen what is the percent bymass of oxygen in magnesium oxide
68 When mercury oxide is heated it decomposes intomercury and oxygen If 284 g of mercury oxidedecomposes producing 20 g oxygen what is the per-cent by mass of mercury in mercury oxide
Law of Multiple Proportions (34)69 Carbon reacts with oxygen to form two different com-
pounds Compound I contains 482 g carbon for every644 g of oxygen Compound II contains 2013 g carbonfor every 537 g of oxygen What is the ratio of carbonto a fixed mass of oxygen for the two compounds
Mixed ReviewSharpen your problem-solving skills by answering the following
70 Which state of matter is the most compressible Theleast Explain why
Solid Liquid Gas
Energy Released by Carbon
Mass (g) Energy released (kJ)
100 33
200 66
300 99
400 132
84 Chapter 3 MattermdashProperties and Changes
71 Classify each of the following as a homogeneous mix-ture or a heterogeneous mixture (33)
a brass (an alloy of zinc and copper)b a saladc bloodd powder drink mix dissolved in water
72 Phosphorus combines with hydrogen to form phos-phine In this reaction 1239 g of phosphorus com-bines with excess hydrogen to produce 1299 g ofphosphine After the reaction 310 g of hydrogenremains unreacted What mass of hydrogen is used inthe reaction What was the initial mass of hydrogenbefore the reaction
73 A sample of a certain lead compound contains 646grams of lead for each gram of oxygen A second sam-ple has a mass of 6854 g and contains 2876 g of oxy-gen Are the two samples the same
Thinking Critically74 Applying Concepts Air is a mixture of many
gases primarily nitrogen oxygen and argon Coulddistillation be used to separate air into its componentgases Explain
75 Interpreting Data A compound contains elementsX and Y Four samples with different masses wereanalyzed and the masses of X and Y in each samplewere plotted on a graph The samples are labeled I IIIII and IV
a Which samples are from the same compound Howdo you know
b What is the approximate ratio of mass X to mass Yin the samples that are from the same compound
c What is the approximate ratio of mass X to mass Yin the sample(s) that are not from the samecompound
Writing in Chemistry76 Select a synthetic element and prepare a short written
report on its development Be sure to cover recent dis-coveries list major research centers that conduct thistype of research and describe the properties of thesynthesized element
77 Research the life of a scientist other than Mendeleevwho contributed to the development of the modernperiodic table of elements Write a brief biographyof this person and detail his or her scientificaccomplishments
78 The results and interpretations of chemistry experi-ments and studies are recorded and published in liter-ally hundreds of scientific journals around the worldVisit the local library and look at several of the articlesin a chemistry journal such as The Journal of theAmerican Chemical Society Write a brief summary ofyour observations regarding the format and style ofwriting in chemistry
Cumulative ReviewRefresh your understanding of previous chapters byanswering the following
79 What is chemistry (Chapter 1)
80 What is mass Weight (Chapter 1)
81 Express the following in scientific notation(Chapter 2)
a 34 500 d 789b 2665 e 75 600c 09640 f 0002 189
82 Perform the following operations (Chapter 2)
a 107 103
b (14 103) (51 105)c (2 103) (4 105)
83 Convert 65degC to Kelvins (Chapter 2)
84 Graph the following data What is the slope of theline (Chapter 2)
CHAPTER ASSESSMENT3
0 2 4 6 8
Mas
s o
f X
(g
)
40
30
20
10
Mass of Y (g)
II
III
I
IV
Standardized Test Practice 85
Use these questions and the test-taking tip to preparefor your standardized test
Interpreting Tables Use the table to answerquestions 1 and 2
1 What are the values for Cl and F respectively forSample II
a 0622 and 6165b 6165 and 3835c 3835 and 0622d 3835 and 6165
2 Which of the following statements best describes therelationship between the two samples
a The compound in Sample I is the same as in SampleII Therefore the mass ratio of Cl to F in bothsamples will obey the law of definite proportions
b The compound in Sample I is the same as in SampleII Therefore the mass ratio of Cl to F in bothsamples will obey the law of multiple proportions
c The compound in Sample I is not the same as inSample II Therefore the mass ratio of Cl to F inboth samples will obey the law of proportions
d The compound in Sample I is not the same as inSample II Therefore the mass ratio of Cl to Fin both samples will obey the law of multipleproportions
3 After elements A and B react to completion in a closedcontainer the ratio of masses of A and B in the con-tainer will be the same as before the reaction This istrue because of the law of
a definite proportionsb multiple proportionsc conservation of massd conservation of energy
4 All of the following are physical properties of tablesugar (sucrose) EXCEPT
a forms solid crystals at room temperatureb appears as crystals white in colorc breaks down into carbon and water vapor when
heatedd tastes sweet
5 A substance is said to be in the solid state if
a it is hard and rigidb it can be compressed into a smaller volumec it takes the shape of its containerd its matter particles are close together
6 Na K Li and Cs all share very similar chemicalproperties In the periodic table of elements they mostlikely belong to the same
a row c groupb period d element
7 A heterogeneous mixture
a cannot be separated by physical meansb is composed of distinct areas of compositionc is also called a solutiond has the same composition throughout
8 What is the percent by mass of sulfur in sulfuric acidH2SO4
a 3269 c 1631b 6413 d 4857
9 Magnesium reacts explosively with oxygen to formmagnesium oxide All of the following are true of thisreaction EXCEPT
a The mass of magnesium oxide produced equals themass of magnesium consumed plus the mass ofoxygen consumed
b The reaction describes the formation of a newsubstance
c The product of the reaction magnesium oxide is achemical compound
d Magnesium oxide has physical and chemicalproperties similar to both oxygen and magnesium
10 Which of the following is NOT a chemical reaction
a dissolution of sodium chloride in waterb combustion of gasolinec fading of wallpaper by sunlightd curdling of milk
STANDARDIZED TEST PRACTICECHAPTER 3
When Eliminating Cross It Out Considereach answer choice individually and cross outchoices yoursquove eliminated If you canrsquot write in thetest booklet use the scratch paper List the answerchoice letters on the scratch paper and cross themout there Yoursquoll save time and stop yourself fromchoosing an answer yoursquove mentally eliminated
Mass Analysis of Two ChlorinendashFluorineCompound Samples
Sample Mass chlorine Mass fluorine Cl F(g) (g)
I 13022 6978 6511 3489
II 5753 9248
chemistrymccomstandardized_test