Classification of Matter

C H A P T E R N I N E CLASSIFICATION OF MATTER

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9 C L A S S I F I C A T I O N O F M A T T E RC H A P T E R N I N E

Did you ever watch a construction crew pour concrete for a building? What is concrete? Actually, you can’t classify fresh concrete as only one of the states of matter. Rather, it is a mixture of solids–Portland cement, sand, rocks–and a liquid, water. Do the following activity to make some classroom concrete and observe its properties. As you study the chapter, you’ll find out more about this and other matter around you.

S e c t i o n 9 – 1

Compostion of Matter

Substances

Mixtures

S e c t i o n 9 – 2

Science and Society Technology:

The Colloid Connection

S e c t i o n 9 – 3

Describing Matter

Physical Properties

Physical Changes

Chemical Properties

Chemical Changes

The Conservation of Mass

PREVIEWING THE CHAPTER

Fresh concrete is not a simply a state of matter. Rather, it is a mixture of solids and a liquid. These solids include sand, pebbles, and calcium carbonate. wwThe liquid is water. The image to the left is forms of concrete.

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9 – 1

SCIENCE WORDS element

compound

substance

homogeneous mixture

heterogeneous mixture

solution

colloid

tyndall effect

suspension

C O M P O S I T I O N O F M A T T E R

You can easily tell whether a line is drawn in ink or pencil.

The lines look different because they are made of different

materials Look at Figure 9–1. Notice that a pencil is made

of several kinds of materials. You could easily classify the

materials of the pencil according to the four states of matter.

Another way to classify materials is by the units they are

made of.

Elements The units that make up all matter are called atoms. If all the

atoms in a sample of matter have the same identity, that

kind of matter is an element. The carbon used in a pencil

point contains only carbon atoms. Carbon is an element.

The copper in a penny is an example of another element. In

a pure copper sample, all the atoms have the same identity.

Altogether, there are 111 recognized elements. The names of

most of the elements are in a table on pages 732–733.

Compounds Materials called compounds are made from atoms of two or

more elements that are combined. The ratio of the different

atoms in a compound is always the same. For example, the

elements hydrogen and oxygen can combine to form the

compound water. The atoms of elements in water are present

in the ratio of two hydrogen atoms to one oxygen atom.

When was the last time you ate a compound whose elements

are a black solid and two invisible gases? One compound that

fits this description is sugar. You can recognize sugar by its

FIGURE9 – 1

A pencil is made up of several different materials.

AN ELEMENT IS MATTER CONSISTING OFonly one kind of atom


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Sugar is a compound of oxygen, hydrogen, and carbon.

Permenant–press fabrics are mixtures that have variable composition.

white crystals wand sweet taste. But the elements that form

sugar–carbon, hydrogen, and oxygen–are neither white nor

sweet, as shown in Figure 9–2. Like sugar, compounds usually

have a different appearance from the elements that make them

up. Oxygen, carbon, water, sugar, baking soda, and salt are

examples of materials classified as substances. A substance is

either an element or a compound. Elements and compounds

cannot be reduced to more basic components by physical

processes.

Mixtures When you have a sore throat, do you gargle with salt water?

Salt water is classified as a mixture. A mixture such as salt

water is a material made up of two or more substances that

can be separated by physical means. Unlike compounds,

mixtures do not always contain the same amounts of different

substances that make them up. You may be wearing clothing

made of permanent–press fabric. This fabric is a mixture of

fibers of two materials–polyester and cotton. The fabric may

contain varying amounts of polyester and cotton, as shown

by the labels in Figure 9–3. Fabric with more polyester is more

resistant to wrinkling than is fabric with less polyester.

FIGURE9 – 3

FIGURE9 – 2

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A mixture in which different materials can be easily

distinguished is called a heterogeneous mixture. Permanent-

press fabrics are heterogeneous mixtures, and you can detect

the different materials by sight or with a microscope. Granite,

concrete, pizza, and dry soup mixes are examples of other

heterogeneous mixtures.

Solutions The salt water you gargle with looks like water and tastes salty.

Like a polyester-cotton fabric, salt water is in some ways similar

to the substances it contains. But you can’t see the particles in

salt water even with a microscope. A material, such as salt water,

in which two or more substances are uniformly spread out, is a

homogeneous mixture.

For example, rubbing alcohol is a common disinfectant. It

appears clear, even though it made up of particles of alcohol in

water. A solution is another name for a homogeneous mixture.

Particles in solutions are so small they cannot be seen even

with a microscope. The particles have diameters of about 0.000

000 001 m (1nm). These particles will never settle to the bottom

of their container. Solutions remain constantly and uniformly

mixed. Substances and mixtures are summarized in Figure 9–4.

MATTER

SUBSTANCE

ELEMENT COMPOUND HOMOGENEOUS HETEROGENEOUS

MIXTURE

has mass and takes up space

compositiondefinite

compostion variable

one kindof atom

HOW CAN MIXTURES BE SEPERATED?

PROCEDURE

ANALYSIS

two or morekinds of atoms

evenly mixed;a solution

unevenly mixed

FIGURE9 – 4

Every sample of matter is an element, a compound, or a mixture. Which of these types of matter are substances?

MINI LAB

find out about the nature of a heterogeneous mixture.

Put equal amounts of soil, clay, sand, gravel, and pebbles in a clear plastic gallon jar. Add water until the jar is almost full.

What order did the materials settle?

Stir or shake the mixture thoroughly. Predict the order in which the materials will settle.

Explain why the materials settled in the order they did.

Observe what happens and compare your observations to your predictions.

How could the individual materials in such a material be seperated?

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PROBLEM SOLVING

THINK CRITICALLY

COOKING A COLLOID The term colloid comes from the Greek word for glue. Gelatin,

which is used to make some types of glue, was on the first

colloids studied. Gelatin consists of large strands of small units

that are twisted and held together by weak attractions. Heat from

boiling water is sufficient to break these attractions and uncoil the

strands. When the strands are cooled, the attractions re–form, but

the strands are tangled into new positions with water trapped in

the spaces between the strands. This creates a semisolid colloid.

Presweetened gelatin desserts have a sweetner, such as

sugar or aspratame, added to the dry gelatin. This sweetner helps

disperse the dry gelatin in the hot water to which it is added. But

unsweetened gelating is first added to cold water, and then the

cold water is heated. Why is unsweetened gelatin added to cold

water instead of hot water?

What role does boiling water play in the formation of the colloid?

The strands of most of the collagen in gelatin must be seperated

and dispersed in order to avoid clumps in the final product. How

does cold water assist this process?

Could presweetened gelatin desserets be added to cold water

and then heated? Explain.

Colloids and Suspensions When you drink a glass of whole or low-fat milk, you

are drinking a mixture of water, fats, proteins, and other

substances. Milk is a colloid. A colloid is a heterogeneous

mixture that, like a solution, never settles. One way to

tell a colloid from a solution is shown in Figure 9–5. Milk

appears white because its particles scatter light. The

scattering of light by particles in a mixture is called the

Tyndall effect. You can see the Tyndall effect in colloids.

FIGURE9 – 5

Unlike the particles of a soluton, the particles in a colloid are large enough to scatter light.

Gelatin is a colloid that may seem to be clear until you shine a light on it. Then you see that its particles scatter light.

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Some mixtures are neither solutions nor colloids. If you fill a glass

with pond water, you may notice that the water is slightly muddy.

If you let it stand long enough, the silt will fall to the bottom of the

glass and the water will appear clear. River deltas are examples of

what happens when muddy water slows down and suspended soil

particles settle out. Muddy water is a suspension. A suspension is a

heterogeneous mixture containing a liquid in which visible particles

settle. Another example of a suspension is glacial meltwater, which

has a milky appearance. Particles carried by the meltwater settle out,

forming glacial deposits such as alluvial fans.

Table 9–1 summarizes how the different types of mixtures

vary in characteristics. You can use the information in this table to

classify different kinds of mixtures.

DESCRIPTION SUSPENSIONSSOLUTIONS COLLOIDS

Settle upon standing

Can be seperated using filter paper

Sizes of particles

Scatter light

No

No

0.1–1 nm

No

No

No

1–100 nm

Yes

Yes

Yes

Greater than 100 nm

Yes

COMPARING SOLUTIONS, COLLOIDS, AND SUSPENSIONS

SECTION WRAP–UP

REVIEW

C O M PA R I N G A N D C O N T R A S T I N G

In terms of suspensions and colloids, compare and contrast a glass of milk and a glass of grapefruit juice. If you need help, refer to Comparing and Contrasting in the Skill Handbook.

THINK CRITICALLY: Why do the words “Shake well before using” on a bottle of fruit juice indicate that the juice is a suspension?

How is a container of hydrogen gas and oxygen gas different from a container of water vapor?

Distinguish between a substance and a mixture.

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2.

3.

skill builder

Most milk containers carry the lable Homogenized. Find out what part of the milk is homogenized and describe the process in your Science Journal.

LIFE SCIENCEconnect to


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ACTIVITY 9 – 1

E L E M E N T S , C O M P O U N D S , A N D M I X T U R E S Elements, compounds, and mixtures all contain atoms. In elements, the atoms all have the same identity. In compounds, two or more elements have been combined in a fixed ratio. In a mixture, the ratio of substances present can vary.

PROCEDURE

ANALYZE

CONCLUDE AND APPLY

DATA AND OBSERVATIONS

PROBLEM

MATERIALS

What are some differences among elements, compounds, and mixtures?

plastic freezer bag containing the following labeled items

copper foil

small package of salt

piece of solder

aluminum foil

chalk (calcium carbonate) or baking soda (sodium hydrogen carbonate)

piece of granite

sugar water in a vial

Use the data table to identify each object and classify it as either an element, a compound, a heterogeneous mixtur, or a homogeneous mixture. The names of all the elements appear in the periodic table on pages 732–733. Any of the objects that are compounds have been named as examples in Section 9–1.

Copy the data to your table into your Science Journal and use it record your observations.

Obtain a prepared bag or numbered objects.

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Were the mixtures you identified homogeneous or heterogeneous?

If you know the name of a substance, how can you find out whether it is an element?

How is a compound different from a mixture?

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Examine the contents of your refridgerator at home. Classify what you find as elements, compounds, or mixtures.

If they are described, all materials can be classified. Compare and contrast elements, compounds, and mixtures.

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OBJECT IDENTITY CLASSIFICATION

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9 – 2 T E C H N O L O G Y : T H E C O L L O I D C O N N E C T I O N

coagulation

A Water–Purifying Colloid Most of us just turn a tap for a drink of fresh water. Did you

realize that a useful colloid may help make this possible? In

most municipal water–treatment plants, water is first taken

from a river and quickly filtered. Then it is allowed to settle

some of the clays and other suspended materials. However,

many fine particles still remain in the water, and they need

to be removed. Water sanitation engineers have developed

techniques that use colloids to remove these fine particles.

Figure 9–6 shows how such a colloid is formed

and used. The newly formed colloid has a fluffy, gel–like

appearance. It is capable of trapping microorganisms and

many of the finely dispersed particles that escaped filtering

because some of the particles stick to the gel.

This image shows the genetic makeup of a colloid.

SCIENCE WORDS

FIGURE9 – 6

Don’t cry over spilt milk!


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Breaking up a ColloidColloids are not always helpful. Some colloids may cause

pollution rather than ridding the environment of pollutants.

For example, a familiar sight around some factories is

large smokestacks with columns of dense smoke billowing

skyward. In addition to materials that can’t be seen,

smoke may contain significant amounts of carbon and

uncombusted coal fragments. These particles make up

soot, which is suspended in the air. To avoid polluting the

air, this colloid must be broken up before it is released into

the atmosphere. The colloid structure is destroyed in a

process called coagulation. In coagulation, small, suspended

particles are attracted to each other. They clump together,

forming a particle that is too large to remain suspended.

Engineers have designed a way to remove most of

the soot in smokestack exhaust in industrial locations, as

shown in Figure 9–7. The particles can be collected later for

further disposal.

FIGURE9 – 7

The soot colloid is vented into a chamber where it is subjected to a high voltage. At this point, the soot particles become negatively charged. They attract uncharged soot particles, and these larger particles are then attracted to a postive part of the chamber, where they accumulate. If soot is effectively removed, the products from a smoke stack appear much cleaner.

SECTION WRAP–UP

REVIEWEven though water is settled and filtered, it is still often treated with a colloid before it is used for drinking. Explain what advantages colloid treatment has for purifying water.

Heating a colloid often causes the velocities of the particles to increase to a level at which high–impact collisions cause them to coagulate. In your Science Journal, explain why it is necessary to use some other technique when coagulating soot in smoke.

How does smoke fit the definition of a colloid?

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explore the technology

COLLOIDS ARE NOT ALWAYS HELPFUL

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9 – 3 D E S C R I B I N G M A T T E R

physical property

physical change

chemical change

chemical property

law of conservation of mass

Physical Properties You can bend an empty aluminum can, but you can’t bend a

piece of chalk. Chalk doesn’t bend–it breaks. Brittleness is a

characteristic that describes chalk. Its color and shape also

describe the chalk. Any such characteristic of a material that

you can observe without changing the substances that make

up the material is a physical property. Examples of physical

properties you have learned about are color, shape, size,

density, melting point, and boiling point. You can describe

matter using physical properties. Look at Figure 9–8. Does all

matter have physical properties?

Some physical properties describe the appearance of

an object. For example, you might describe an iron nail as

a pointy–ended cylinder made of a dull, gray–colored solid.

By describing the shape, color, and state of the nail, you

have listed several of its physical properties. Some physical

properties can be measured. For instance, you could use a

metric ruler to measure one property of the nail–its length.

What physical property of the nail is measured with a balance?

FIGURE9 – 8

Each of the items pictured has it’s own properties. What are the physical properties of the DVD cases?

SCIENCE WORDS

Is the length of a nail most likely to be 3mm, 3cm, or 3km?

USING MATH


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If you had a soft drink in a cup, you could measure its

volume and temperature and describe its odor. Each of these

characteristics is a physical property of the soft drink. Some

physical properties describe the behavior of a material or a

substance. As you may know, all objects made of iron are

attracted by a magnet. Attraction by a magnet is a property

substance of iron. Every substance has physical properties that

distinguish it from other substances.

Identification by Properties Do you pick out the grapes in a fruit salad and eat them first, last,

or maybe not at all? If you do, you are using physical properties

to identify the grapes and separate them from the other fruits in

the mixture. Figure 9–9 shows a mixture of pebbles and sand.

You can identify the pebbles and grains of sand by differences

in color, shape, and size. By sifting the mixture, you can quickly

separate the pebbles from the grains of sand because they are

different sizes.

Now look at the mixture of iron fillings and sand shown

in Figure 9–10B. It would be impossible to separate this mixture

with a sieve because the filings and grains of sand are the

same size. A more efficient way is to pass a magnet through

the mixture. When you pass a magnet through the mixture, the

magnet attracts the iron filings and pulls them from the sand. In

this way, the difference in a physical property, such as attraction

to a magnet, can be used to separate substances in a mixture. A

practical example of using the physical property of magnetism is

shown in Figure 9–10A.

FIGURE9 – 9

This mixture of pebbles and sand can be seperated by physical means, such as using different sizes of filters.

Iron can be seperated from other materials because it has the physical property of magnetism. The iron in these materials to be recycled can be seperated by a magnet.

FIGURE9 – 10

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Physical Changes If you break a piece of chalk, its original size and shape change. You

have caused a change in some of its physical properties. But you

have not changed the identity of the substance that makes up the

chalk.

The changes in state that you studied in Chapter 8 are all

examples of physical changes. When a substance freezes, boils,

evaporates, sublimes, or condenses, it undergoes physical changes

such as those shown in Figure 9–11. Energy changes occur during

these changes in state, but the kind of substance– the identity of the

element or compound– does not change.

The Identity Remains the Same As shown in the picture above, iron will change states if it absorbs

or loses enough energy. In each state, it will have physical properties

that identify it as the substance iron. A change in size, shape, or state

of matter is called a physical change. Sometimes, a color change

indicates a physical change. Physical changes do not change the

identities of the substances in a material.

Just as physical properties can be used to separate mixtures,

so can physical changes. For example, if you let a cup of salt

FIGURE9 – 11

When iron melts and then re–cools, physical changes occur. Does the identity of iron change?

Recycling conserves natural resurces. In some large recycling projects, it is difficult to seperate aluminum metal from scrap iron. Investigate the physical properties of the two metals that would help you seperate them.

EARTH SCIENCEconnect to


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water stand for a week, you’ll find that the water has

evaporated, leaving salt crystals inside the cup. The

process of evaporating water from salty seawater is

used to produce drinking water.

Chemical Changes From observations of what happens around you, you

know that changes do occur in which substances change

their identities. Fireworks explode, matches burn, eggs

rot, and bikes and car bodies rust. What do changes in

these materials have in common?

Burned toast, burned soup, and burned steak

all smell burned. The smell is different from the smell

of bread, soup, or steak. The odor is a clue that a

new substance has been produced. A change of one

substance in a material to a different substance is called

a chemical change. Many signs can tell you when a

chemical change has taken place. For example, the

foaming of an antacid tablet in a glass of water and the

smell in the air after a thunderstorm indicate that new

substances have been produced. In some changes a

rapid production of energy, such as the light and sound

of an exploding firecracker, is a clue.

USING TECHNOLOGY aerogels

Imagine a block of gelatin dessert in which all of the liqiud has been been replaced with air. It might look like a frozen cloud and would be called an aerogel. Light passing through the tiny pores and microscoping framework of an aerogel is bent, giving the aerogel a bluish color against a dark background and a yellowish color in the light. The framework is so weakly connected that the aerogel is a poor conductor of heat and an excellent insulator. This insulating property of aerogels has caught he interest of industry. Aerogels can be used to replace the current foam insulation used in refrigerators. A one–inch thick aerogel in a double–pane window insulates as well as 30 layers of glass. They block sound so well that the Navy may use them to reduce noise levels in submarines. They are ideal for cameras that focus by response to sound waves. A black, pure–carbon aerogel has also been made that is an excellent conductor of electricity. Using this aerogel, it would be possible to create a car part that would hold enough electrical charge to accelerate an electric vehicle from a standstill without draining the battery.

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A Change in Identity When iron is exposed to oxygen and water is in the air, the iron

and oxygen slowly form a new substance, rust. When hydrogen

gas is burned in a rocket engine, the elements hydrogen and

oxygen combine to form water. Burning and rusting are chemical

changes because different substances are produced.

Weathering: Chemical or Physical Change? The effects of nature’s forces on Earth’s surface provide many

opportunities to observe dramatic changes. Steep canyon walls,

shifting sand dunes, and unusual limestone formations are easily

observed at various global locations. Would you classify the

changes that caused these formations as physical changes or

chemical changes? Geologists, using the same criteria that you

have learned in this chapter would classify some weathering

changes as physical and some as chemical changes.

Large rocks can split when water seeps into small cracks,

freezes, and expands. However, the smaller pieces of newly

exposed rock still have the same properties as the original

sample. This change is a physical change. Limestone, shown in

Figure 9–12, may be washed away by rain and moving rivers,

which is another physical change. Sometimes, however, the

water is acidic. If this is the case, that changes may produce

new products. Solid calcium carbonate, a compound found in

limestone, does not easily dissolve in water. This change in

limestone would be classed as a chemical change because the

identity of the calcium carbonate changes. The mineral feldspar

is also susceptible to acid attack.

FIGURE9 – 12

Calcium carbonate is found in cave formations and on earth’s surface in formations such as the White Cliffs of Dover, England.

A CHANGE OF ONE SUBSTANCEINTO ANOTHER SUBSTANCE IS Achemical change


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Chemical Properties Look at Figure 9–13. You have probably seen these warnings on

cans of paint thinners and lighter fluids for charcoal grills. The

warnings indicate that these liquids burn quickly. The tendency

of a substance to burn is an example of a chemical property.

A chemical property is a characteristic of a substance that

indicates whether it can undergo a certain chemical change.

Many substances are flammable or combustible. Knowing which

materials contain substances that have this chemical property

allows you to use them safely.

If you look around the drugstore, you might notice that

many medicines are stored in dark bottles. These medicines

contain compounds with a similar chemical property. Chemical

changes will take place in the compounds if they are exposed

to light. What physical property do these bottles have in

common?

Even though there are thousands of substances and billions

of mixtures, they do share a few common physical and chemical

properties. You can use these properties to study matter further.

FIGURE9 – 13

Flammability or combustibility is a chemical property of some materials used in the home. How do flammability and combustibility differ?

Over the past couple of days, you have observed or been part of many chemical and physical changes. In your Science Journal, describe five chemical changes and five physical changes that you have noticed in the past two days.

SCIENCE JOURNAL

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The Conservation of Mass Wood is combustible, or burnable, which is a chemical property.

Suppose you burn a large log on a campfire until nothing is left

but a small plate of ashes. During the burning, smoke, heat, and

light are given off. It’s easy to see that a chemical change occurs.

At first, you might also think that matter was lost during this

change because the pile of ashes looks much smaller than the

log. In fact, if you could measure booth the mass of the log and

the mass of the ashes, the mass of the ashes would be less than

that of the log. But suppose that during the burning, you could

collect all the oxygen in the air that was combined with the log

during the burning. And suppose you could collect all the smoke

and gases that escape from the burning log and measure their

masses, too. Then you would find that there is no loss of mass

during the burning, as shown in Figure 9–14.

Not only is there no loss of mass during burning, there

is no loss or gain of mass during any chemical change. In other

words, matter is neither created nor destroyed during a chemical

change. This statement is known as the law of conservation of

mass. According to this law, the mass of all substances present

before a chemical change equals the mass of all the substances

remaining after the change. How does Figure 9–15 illustrate the

law of conservation of mass?

WHAT ARE SOME INDICATIONS OF CHANGE?

PROCEDURE

ANALYSIS

MINI LAB

Discover some clues that indicate that a physical or chemical change has occured.

Add water to a 250–mL beaker until it is half–full.

Is dissolving a chemical or physical change?

Add a crystal of potassium permanganate to the water and observe what happens.

What evidence of chemical change did you see?

Add 1 g of sodium hydrogen sulfite to the solution and stir until the solution becomes colorless.

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FIGURE9 – 14

Although you can’t see the gasses used or formed when the log burns, there is no loss or gain of mass. What gass is necessary for burning to take place?


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Why do substances have physical and chemical properties

and undergo physical and chemical changes? These properties

and changes are the result of what atoms are present and

how they are arranged. The composition and arrangement are

different for each substance.

SECTION WRAP–UP

REVIEWIn terms of substances, explain why evaporation of water is a physical change and not a chemical change.

Give an exampe of a chemical change that occurs when you prepare a meal.

Why is being flammable a chemical property rather than a physical property.

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4. THINK CRITICALLY: The law of conservation of mass applies to physical changes as well as chemical changes. How might you demonstrate this law for melting ice?

O B S E R V I N G A N D I N F E R R I N G

Observe a burning candle. What evidence do you have that there are chemical and physical changes in the candle as it burns? If you need help, reder to Observing and Inferring in the Skill Handbook.

skill builder

Two chemicals with a combined mass of 28.48 g react in a flask that has a mass of 142.05 g. A gas is produced that totally escapes into a flask that has an empty mass of 141.65 g. After the reaction, the first flask and its contents have a mass of 167.16 g. Calculate the total mass of the second flask and gas.

FIGURE9 – 15

A chemical change between two eggs demonstrates the law of conservation of mass.

USING MATH

Classification of Matter

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