Unit 6 Science (Glencoe Red 2002)

U N I T

524

How AreTrain Schedules

& Oil PumpsConnected?

How AreTrain Schedules

& Oil PumpsConnected?

6 Matter, Forces,and Energy6

SCIENCE CONNECTIONSCIENCE CONNECTION

FRICTION AND LUBRICANTS A lubricant is a substance that reduces frictionbetween surfaces that touch one another. Some of the world’s first lubricantswere animal and plant products such as lard and vegetable oils. Conduct researchto identify a variety of modern-day lubricants. Select one lubricant you learnedabout and create a poster that shows its source, how it is made or processed, itsspecial properties, and how it is used to reduce friction.

In the 1800s, trains had to make frequent stops so that their moving parts could be lubricated.Without lubrication, the parts would have worn out due to friction. When the train stopped, a

worker had to get out and oil the parts by hand. The process was very time-consuming and madeit hard for trains to stay on schedule. Around 1870, an engineer named Elijah McCoy developedthe first automatic lubricating device, which oiled the engine while the train was running. (Alater version of his automatic lubricator is seen at lower right.) Since then, many kinds of auto-matic lubricating devices have been developed. Today, automobiles have oil pumps that auto-matically circulate oil to the moving parts of the engine. When you go for a ride in a car, you canthank Elijah McCoy that you don’t have to stop every few miles to oil the engine by hand!

Wendy Craig Duncan car-ried the Olympic flameunderwater on the way to

the 2000 Summer Olympics in Syd-ney, Australia. How many differentstates of matter can you find in thispicture? What chemical and physicalchanges are taking place? In thischapter, you will learn about the fourstates of matter, the physical andchemical properties of matter, andhow those properties can change.

What do you think?Science Journal What is the coloredband on this fish tank? Why would itchange colors? Here’s a hint: Wouldyou want your fish to be chilly? Writeyour thoughts and ideas in your Science Journal.

Properties andChanges of Matter

526

1818

527

Your teacher has given you a collection of pennies.It is your task to separate these pennies into

groups while using words to describe each set. In thischapter, you will learn how to identify things basedon their physical and chemical properties. With an

understanding of these principles of matter, you will discover how things areclassified or put into groups.

Classify coins1. Observe the collection of pennies.

2. Choose a characteristic that willallow you to separate the penniesinto groups.

3. Classify and sort each penny based on the chosen feature.Tally your data in a frequency table.

4. Explain how you classified the pennies. Compare your system of classification with those of others in the classroom.

ObserveThink about how your group classified its pennies. Describe the system yourgroup used in your Science Journal.

EXPLOREACTIVITY

527

Making an Organizational Study Fold Make the following Foldable to help you organize your thoughts into clear categoriesabout properties of matter.

1. Place a sheet of paper in front of you so the long side is at the top.Fold the paper in half from the left side to the right side. Unfold.

2. Fold each side in to the center fold line to divide the paper intofourths. Fold the paper in half from top to bottom. Unfold.

3. Through the top thickness of paper, cut along both of the middle foldlines to form four tabs. Label the tabs Physical Properties, PhysicalChanges, Chemical Properties, and Chemical Changes.

4. Before you read the chapter, define each term on the front of the tabs.As you read the chapter, correct your definitions and write about each under the tabs.

FOLDABLESReading & StudySkills

Physical

Properties

Physical

Changes

ChemicalProperties

ChemicalChanges

Physical Properties and Changes

S E C T I O N

Using Your SensesAs you look in your empty wallet and realize that your

allowance isn’t coming anytime soon, you decide to get an after-school job. You’ve been hired at the new grocery store that willopen next month. They are getting everything ready for thegrand opening, and you will be helping make decisions aboutwhere things will go and how they will be arranged.

When you come into a new situation or have to make anykind of decision, what do you usually do first? Most peoplewould make some observations. Observing involves seeing,hearing, tasting, touching, and smelling.

Whether in a new job or in the laboratory, you use yoursenses to observe materials. Any characteristic of a material thatcan be observed or measured without changing the identity ofthe material is a physical property. However, it is important tonever taste, touch, or smell any of the materials being used inthe lab without guidance, as noted inFigure 1. For safety reasons you willrely mostly on other observations.

■ Identify physical properties of matter.

■ Describe the states of matter.■ Classify matter using physical

properties.

Vocabularyphysical property state of mattermatter melting pointphysical change boiling pointdensity

Observing physical properties will help you interpret the worldaround you.

Figure 1For safety reasons, inthe laboratory youusually use only twoof your senses—sightand hearing. Manychemicals can be dan-gerous to touch,taste, and smell.

528

Watch

Listen

Do NOTtouch

Do NOTsmell

Do NOTtaste

Physical PropertiesOn the first day of your new job, the boss gives you an

inventory list and a drawing of the store layout. She explainsthat every employee is going to give his or her input as to howthe merchandise should be arranged. Where will you begin?

You decide that the first thing you’ll do is make some obser-vations about the items on the list. One of the key senses used inobserving physical properties is sight, so you go shopping tolook at what you will be arranging.

Color and Shape Everything that you can see, touch, smell,or taste is matter. Matter is anything that has mass and takes upspace. What things do you observe about the matter on yourinventory list? The list already is organized by similarity of prod-ucts, so you go to an aisle and look.

Color is the first thing you notice. The laundry detergentbottles you are looking at come in every color. Maybe you willorganize them in the colors of the rainbow. You make a note andlook more closely. Each bottle or box has a different shape.Some are square, some rectangular, and some are a free-formshape. You could arrange the packages by their shape.

When the plastic used to make the packaging is molded, itchanges shape. However, the material is still plastic. This type ofchange is called a physical change. It is important to realize thatin a physical change, the physical properties of a substancechange, but the identity of the substance does not change.Notice Figure 2. The detergent bottles are made of high-densitypolyethylene regardless of the differences in the physical proper-ties of color or shape.

What is matter?

SECTION 1 Physical Properties and Changes 529

Research Visit the Glencoe Science Web site at science.glencoe.com for more information aboutclassifying matter by its phys-ical properties. Communicateto your class what you learn.

Figure 2 The identity of the material does not necessarily depend onits color. Each of these bottles is made of high-density polyethylene (HDPE).

http://science.glencoe.com

Length and Mass Some properties of matter can be identi-fied by using your senses, and other properties can be measured.How much is there? How much space does it take up?

One useful and measurable physical property is length.Length is measured using a ruler, meterstick, or tape measure,as shown in Figure 3. Objects can be classified by their length.For example, you could choose to organize the French breadin the bakery section of your store by the length of the loaf.But, even though the dough has been shaped in differentlengths, it is still French bread.

Back in the laundry aisle, you notice a child struggling to liftone of the boxes of detergent. That raises a question. How muchdetergent is in each box? Mass is a physical property thatdescribes the amount of material in an object. Some of theboxes are heavy, but, the formula of the detergent hasn’tchanged from the small box to the large box. Organizing theboxes by mass is another option.

Volume and Density Mass isn’t the only physical propertythat describes how much of something you have. Anothermeasurement is volume. Volume measures the amount ofspace an object takes up. Liquids usually are measured byvolume. The juice bottles on your list could be organized by volume.

Another measurable physical property related to mass andvolume is density—the amount of mass a material has for agiven volume. You notice this property when you try to lift twothings of equal volume that have different masses. Density isfound by dividing the mass of an object by its volume.

density � mass�volume, or D � m�V

530 CHAPTER 18 Properties and Changes of Matter

Collect Data Visit the Glencoe Science Web site atscience.glencoe.com forinformation about density.Communicate to your classwhat you learn.

Figure 3 The length of any object can be measured with the appropriate tool.


Same Volume, Different Mass Figure 4 shows two ballsthat are the same size but not the same mass. The bowling ball ismore dense than the kickball. The customers of your grocerystore will notice the density of their bags of groceries if the bag-gers load all of the canned goods in one bag and put all of thecereal and napkins in the other.

The density of a material stays the same as long as pressureand temperature stay the same. Water at room temperature has adensity of 1.00 g/cm3. However, when you do change the temper-ature or pressure, the density of a material can change. Water keptin the freezer at 0°C is in the form of ice. The density of that ice is0.9168 g/cm3. Has the identity of water changed? No, but some-thing has changed.

What two measurements are related in themeasurement of density?

States of Matter What changes when water goes from 20°C to 0°C? It

changes from a liquid to a solid. The four states of matter aresolid, liquid, gas, and plasma (PLAZ muh). The state of mat-ter of a substance depends on its temperature and pressure.Three of these states of matter are things you talk about orexperience every day, but the term plasma might be unfamil-iar. The plasma state occurs at very high temperatures and isfound in fluorescent (floo RE sunt) lightbulbs, the atmo-sphere, and in lightning strikes.

As you look at the products to shelve in your grocery store,you might make choices of classification based on the state ofmatter. The state of matter of a material is another physicalproperty. The liquid juices all will be in one place, and the solid,frozen juice concentrates will be in another.


Figure 4 These balls take up about thesame space, but the bowlingball on the left has more massthan the kickball on the right.Therefore, the bowling ball ismore dense.

Changing DensityProcedure1. Stir three tablespoons of

baking soda in 3/4 cup ofwarm water. Set aside.

2. Pour vinegar into a clearglass until it is half full.

3. Slowly pour the baking sodaand warm water mixtureinto the glass of vinegar.

4. After most of the fizzing hasstopped, place three halvesof raisins in the glass.

5. Record your observations inyour Science Journal or on acomputer.

Analysis1. How did the bubbles affect

the raisins?2. Infer what changed the

density of the raisins.

Bowling ball Kickball

Moving Particles Matter is made up of moving particles.The state of matter is determined by how much energy the par-ticles have. The particles of a solid vibrate in a fixed position.They remain close together and give the solid a definite shapeand volume. The particles of a liquid are moving much fasterand have enough energy to slide past one another. This allows aliquid to take the shape of its container. The particles of a gas aremoving so quickly that they have enough energy to move freelyaway from other particles. The particles of a gas take up as muchspace as possible and will spread out to fill any container.Figure 5 illustrates the differences in the states of water.

Which state of matter doesn’t conform to theshape of the container?

Changes of State You witness a change of state when youput ice cubes in water and they melt. You still have water but inanother form. The opposite physical change happens when youput liquid water in ice-cube trays and pop them in your freezer.The water doesn’t change identity—only the state it is in.

For your job, you will need to make some decisions based onthe ability of materials to change state. You don’t want all thosefrozen items thawing out and becoming slushy liquid. You alsodon’t want some of the liquids to get so cold that they freeze.


Solid water Liquid water Gaseous water

Figure 5 Water can be in three differentstates: solid, liquid, and gas. Themolecules in a solid are tightlypacked and vibrate in place, butin a liquid they can slip past eachother because they have moreenergy to move. In a gas, theymove freely all around the con-tainer with even more energy.

Melting and Boiling Points Atwhat temperature will water in theform of ice change into a liquid? Thetemperature at which a solid becomesa liquid is its melting point. Themelting point of a pure substancedoes not change with the amount ofthe substance. This means that asmall sliver of ice and a block of icethe size of a house both will melt at0°C. Lead always melts at 327.5°C.When a substance melts, it changesfrom a solid to a liquid. This is aphysical change and the melting pointis a physical property.

At what temperature will liquidwater change to a gas? The boilingpoint is the temperature at which a substance in the liquid statebecomes a gas. Each pure substance has a unique boiling point atatmospheric pressure. The boiling point of water is 100°C atatmospheric pressure. The boiling point of nitrogen is �195.8°C,so it changes to a gas when it warms after being spilled into theopen air, as shown in Figure 6. The boiling point, like the meltingpoint, does not depend on the amount of the substance.

What physical change takes place at the boiling point?

However, the boiling point and melting point can help toidentify a substance. If you observe a clear liquid that boils at56.1°C at atmospheric pressure, it is not water. Water boils at100°C. If you know the boiling points and melting points of sub-stances, you can classify substances based on those points.

Metallic PropertiesOther physical properties allow you to classify substances as

metals. You already have seen how you can classify things assolids, liquids, or gases or according to color, shape, length,mass, volume, or density. What properties do metals have?

How do metals look and act? Often the first thing younotice about something that is a metal is its shiny appearance.This is due to the way light is reflected from the surface of themetal. This shine is called luster. New handlebars on a bike havea metallic luster. Words that describe the appearance of non-metallic objects are pearly, milky, or dull.


Figure 6 When liquid nitrogen is pouredfrom a flask, you see an instantchange to gas because nitrogen’sboiling point is –195.8°C, whichis much lower than room temperature.

When geologists describerocks, they use specificterms that have meaning toall other scientists whoread their descriptions. Todescribe the appearance ofa rock or mineral, they usethe following terms: metal-lic, adamantine, vitreous,resinous, pearly, silky, andgreasy. Research theseterms and write a defini-tion and example of each inyour Science Journal.

Liquid nitrogen (below –195.8°C)

Nitrogen gas (above –195.8°C)

Uses of Metals Metals can be used in unique ways becauseof some of the physical properties they have. For example, manymetals can be hammered, pressed, or rolled into thin sheets.This property of metals is called malleability (mal lee uh BIHluh tee). The malleability of copper makes it an ideal choice forartwork such as the Statue of Liberty. Many metals can be drawninto wires as shown in Figure 7. This property is called ductility(duk TIH luh tee). The wires in buildings and most electricalequipment and household appliances are made from copper. Sil-ver and platinum are also ductile.

You probably observe another physical property of somemetals every day when you go to the refrigerator to get milk orjuice for breakfast. Your refrigerator door is made of metal.Some metals respond to magnets. Most people make use of thatproperty and put reminder notes, artwork, and photos on theirrefrigerators. Some metals have groups of atoms that can beaffected by the force of a magnet, and they are attracted to themagnet because of that force. The magnet in Figure 8 is being

used to select metallic objects.At the grocery store, your em-

ployer might think about these prop-erties of metals as she looks at grocerycarts and thinks about shelving. Mal-leable carts can be dented. How couldthe shelf ’s attraction of magnets beused to post advertisements or weeklyspecials? Perhaps the prices could befixed to the shelves with magneticnumbers. After you observe the physi-cal properties of an object, you canmake use of those properties.


Figure 7This artist has taken advantageof the ductility of metal bychoosing wire as the medium for her sculpture.

Figure 8This junkyard magnet pulls scrapmetal that can be salvaged fromthe rest of the debris. It is sortingby a physical property.

Using PhysicalProperties

In the previous pages,many physical propertieswere discussed. These physi-cal properties—such asappearance, state, shape,length, mass, volume, abilityto attract a magnet, density,melting point, boiling point,malleability, and ductility—can be used to help you iden-tify, separate, and classifysubstances.

For example, salt can bedescribed as a white solid.Each salt crystal, if you lookat it under a microscope,could be described as having a three-dimensional cubic struc-ture. You can measure the mass, volume, and density of asample of salt or find out if it would attract a magnet. Theseare examples of how physical properties can be used to iden-tify a substance.

Sorting and Separating When you do laundry, you sortaccording to physical properties. Perhaps you sort by color.When you select a heat setting on an iron, you classify theclothes by the type of fabric. When miners during the GoldRush panned for gold, they separated the dirt and rocks by den-sity of particles. Figure 9 shows a coin sorter that separates thecoins based on their size. Iron filings can be separated from sandby using a magnet.

Scientists who work with animals usephysical properties or characteristicsto determine the identity of a speci-

men. They do this by using a tool called a dichotomous (di KAHtuh mus) key. The term dichotomous refers to two parts or divi-sions. Part of a dichotomous key for identifying hard-shelledcrabs is shown in Figure 10. To begin the identification of yourunknown animal, you are given two choices. Your animal willmatch only one of the choices. In the key in Figure 10, you areto determine whether or not your crab lives in a borrowed shell.Based on your answer, you are either directed to another set ofchoices or given the name of the crab you are identifying.


Figure 9 Coins can be sorted by their phys-ical properties. Sorting by size isused here.

Figure 10

VISUALIZING DICHOTOMOUS KEYS

Whether in the laboratory or in the field, scientists oftenencounter substances

or organisms that they cannot imme-diately identify. One approach totracking down the identity of such“unknowns” is to use a dichotomouskey, such as the one shown. The key isdesigned so a user can compare physi-cal properties or characteristics of theunknown substance or organism—inthis case, a crab—with characteristicsof known organisms in a stepwisemanner. With each step, a choicemust be made. Each choice leads tosubsequent steps that guide the userthrough the key until a positive identi-fication is made.

536 CHAPTER 18

A. Lives in a “borrowed” shell (usually some type of snail shell)

B. Does not live in a “borrowed” shell

A. Shell completely overlaps the walking legs

B. Walking legs are exposed

Hermit Crab

go to #2

Box Crab

Kelp Crab

1.

2.

Dichotomous Key

Can you identify thethree crabs shown hereby following thisdichotomous key?

Everyday Examples Identification by physical properties isa subject in science that is easy to observe in the real world. Sup-pose you volunteer to help your friend choose a family pet.While visiting the local animal shelter, you spot a cute dog. Thedog looks like the one in Figure 11. You look at the sign on thecage. It says that the dog is male, one to two years old, and itsbreed is unknown. You and your friend wonder what breed ofdog he is. What kind of information do you and your friendneed to figure out the dog’s breed? First, you need a thoroughdescription of the physical properties of the dog. What does thedog look like? Second, you need to know the descriptions of var-ious breeds of dogs. Then you can match up the description ofthe dog with the correct breed. The dog you found is a white,medium-sized dog with large black spots on his back. He alsohas black ears and a black mask around his eyes. The manager ofthe shelter tells you that the dog is close to full-grown. Whatbreed is the dog?

Narrowing the Options To find out, you may need to researchthe various breeds of dogs and their descriptions. Often, determin-ing the identity of something that isunknown is easiest by using theprocess of elimination.You figure out all of the breeds the dog can’tbe. Then your list of possible breeds is smaller. Upon looking atthe descriptions of various breeds,you eliminate small dog and largedog breeds. You also eliminate breeds that do not contain whitedogs. With the remaining breeds, you might look at photos to seewhich ones most resemble your dog. Scientists use similar meth-ods to determine the identities of living and nonliving things.

SubstancesMatter—everything that has mass and takes up space—can

be classified by its physical properties. One way to classify mat-ter is based on its chemical composition. Matter that has thesame composition and properties throughout is called a sub-stance. There are two types of substances—elements and com-pounds.

Elements Substances that are made up of only one type ofatom are called elements. Figure 12 shows examples of ele-ments. Oxygen is a substance made up of only oxygen atoms. Abar of gold is a substance made up of only gold atoms. Alu-minum foil is made up of only aluminum atoms. Elements can-not be broken down into simpler substances by physical orchemical means. However, different elements can combine toform new substances—called compounds.


Figure 11Physical descriptions are used to determine the identities ofunknown things. What physicalproperties are used to describe this dog?

Figure 12Elements such as oxygen, gold,and aluminum are made up ofonly one type of atom.

Oxygen

Gold

Aluminum

Compounds What do you call the colorless liquid that flowsfrom the kitchen faucet? You probably call it water, but maybeyou’ve seen it written as H2O. The elements hydrogen and oxy-gen exist separately as colorless gases. However, these two ele-ments can combine to form the compound water, shown inFigure 13, with properties that are different from the individualgases that make it up. A compound is a substance that is madeup of atoms of more than one element chemically bondedtogether. The smallest unit of water is made up of two hydrogenatoms and one oxygen atom bonded together.

Compounds have a fixed ratio—or proportion of atomsthroughout. For example, every drop of water contains a ratio oftwo hydrogen atoms to one oxygen atom. Every sample of car-bon dioxide contains a ratio of one carbon atom to two oxygenatoms.

Compounds can be broken down only by chemical meansinto the elements that combined to make them. For example,boiling, freezing, stirring or filtering will not separate the hydro-gen atoms from the oxygen atom. However, if electricity isadded to water, it can be broken down into hydrogen gas andoxygen gas.

MixturesWhen two or more substances come together but don’t

chemically combine or bond to make a new substance, a mix-ture results. Unlike compounds, the proportions of the sub-stances in a mixture can be changed without changing theidentity of the mixture. For example, if you put some sand intoa bucket of water, the sand doesn’t chemically combine with thewater. If you add more sand or more water, it’s still a mixture ofsand and water. Physical properties can be used to separate mix-tures into simpler substances. For example, solid sand can be fil-tered from liquid water using a sieve.


Figure 13Compounds contain more thanone type of atom bondedtogether.Water contains a ratioof two hydrogen atoms bondedto one oxygen atom.

H2O

Oxygen atom

Hydrogen atoms

O

H

H

Homogeneous Mixtures Mixtures can be classified ashomogeneous or heterogeneous based on their physicalproperties. Homogeneous means “the same throughout.”Homogeneous mixtures contain more than one substanceevenly mixed but not chemically bonded together. You can’tsee the different parts in a homogeneous mixture nomatter how closely you look. In fact, it is difficult tosee the difference between a homogeneous mixtureand a substance because they both look uniform, oreven, throughout.

Homogeneous mixtures can be solid, liquid or gas.The brass in a trumpet is a solid mixture of zinc andcopper—two elements. Sugar water is a homogeneousliquid mixture of sugar and water—both compounds.Air is a homogeneous mixture of elements—nitrogen,oxygen, argon, neon and helium—and two com-pounds—carbon dioxide and water. Another name fora homogeneous mixture is a solution.

Heterogeneous Mixtures A heterogeneous mixture is oneof two or more substances that are not mixed evenly. You cansee the different parts of a heterogeneous mixture, such as amixture of sand and water. A pizza is a tasty kind of heteroge-neous mixture. Other examples of this kind of mixture includesalad, a bookshelf full of books, or a toolbox full of nuts andbolts. Figure 14 shows examples of heterogeneous and homoge-neous mixtures.


Section Assessment

1. What property of matter is used to mea-sure the amount of space an object takes?

2. What are the four states of matter?Describe each and give an example.

3. How might a substance such as water havetwo different densities?

4. Compare and contrast heterogeneous andhomogeneous mixtures.

5. Think Critically Explain why the boilingpoint is the same for 1 L and 3 L of water.Will it take the same amount of time foreach volume of water to begin to boil?

6. Concept Mapping Using a computer, draw acycle concept map with the steps for changingan ice cube into steam. Use the terms meltingpoint and boiling point in your answer. For morehelp, refer to the Science Skill Handbook.

7. Solving One-Step Equations Calculate thevolume of an object that has a length of 10 cm,a width of 10 cm, and a height of 10 cm. Usethe formula for volume: V � lwh. Express youranswer using cubic centimeters (cm3). For morehelp, refer to the Math Skill Handbook.

Figure 14The salad and the pizza are het-erogeneous mixtures.The fruitdrink is a homogeneous mixture.

Chemical Properties and Changes

S E C T I O N

Ability to ChangeIt is time to celebrate. You and your coworkers have cooper-

ated in classifying all of the products and setting up the shelvesin the new grocery store. The store manager agrees to a celebra-tion party and campfire at the nearby park. Several large piecesof firewood and some small pieces of kindling are needed tostart the campfire. After the campfire, all that remains of thewood is a small pile of ash. Where did the wood go? What prop-erty of the wood is responsible for this change?

All of the properties that you observed and used for classifi-cation in the first section were physical properties that youcould observe easily. In addition, even when those propertieschanged, the identity of the object remained the same. Some-thing different seems to have happened in the bonfire example.

Some properties do indicate a change of identity for the sub-stances involved. A chemical property is any characteristic thatgives a substance the ability to undergo a change that results in anew substance. Figure 12 shows some properties of substancesthat can be observed only as they undergo a chemical change.

What does a chemical property give a substancethe ability to do?

■ Recognize chemical properties.■ Identify chemical changes.■ Classify matter according to

chemical properties.■ Describe the law of conservation

of mass.

Vocabularychemical propertychemical changeconservation of mass

Knowing the chemical properties willallow you to distinguish differencesin matter.


Flammability Reacts with oxygen Reacts with light Reacts with water

Figure 12These are four examples of chemical properties.

Common Chemical PropertiesYou don’t have to be in a laboratory to see changes that take

place because of chemical properties. These are called chemicalchanges. A chemical change is a change in the identity of a sub-stance due to the chemical properties of that substance. A newsubstance or substances are formed in such a change.

The campfire you enjoyed to celebrate the opening of the gro-cery store resulted in chemical changes. The oxygen in the airreacted with the wood to form a new substance called ash. Woodcan burn. This chemical property is called flammability. Someproducts have warnings on their labels about keeping them awayfrom heat and flame because of the flammability of the materials.Sometimes after a campfire you see stones that didn’t burnaround the edge of the ashes. These stones have the chemicalproperty of inflammability.

Common Reactions An unpainted iron gate, such as theone shown in Figure 13A, will rust in time. The rust is a result ofoxygen in the air reacting with the iron and causing corrosion.The corrosion produces a new substance called iron oxide.Other chemical reactions occur when metals interact with other elements. Figure 13B shows tarnish, the grayish-brownfilm that develops on silver when it reacts with sulfur in the air.The ability to react with oxygen or sulfur is a chemical property.Figure 13C shows another example of this chemical property.

Have you ever sliced an apple or banana and left it sittingon the table? The brownish coloring that you notice is a chem-ical change that occurs between the fruit and the oxygen in theair. Those who work in the produce department at the grocerystore must be careful with any fruit they slice to use as sam-ples. Although nothing is wrong with brown apples, they don’tlook appetizing.

SECTION 2 Chemical Properties and Changes 541

Figure 13Many kinds of interactions with oxygen can occur.

An untreated iron gate willrust. Silver dishes developtarnish. Copper sculpturesdevelop a green patina, which isa mixture of copper compounds.

Researchers have discov-ered an enzyme in fruitthat is involved in thebrowning process. Theyare doing experiments totry to grow grapevines inwhich the level of thisenzyme, polyphenol oxi-dase (PPO), is reduced.This could result ingrapes that do not brownas quickly. Write a para-graph in your ScienceJournal about why thiswould be helpful to fruitgrowers, store owners,and customers.

Heat and Light Vitamins often are dispensed in dark-brownbottles. Do you know why? Many vitamins have the ability tochange when exposed to light. This is a chemical property. Theyare protected in those colored bottles from undergoing a chemi-cal change with light.

Some substances are sensitive to heat and will undergo a chemical change only when heated or cooled. One example is limestone. Limestone is generally thought of as un-reactive. Some limestone formations have been around for centuries without changing. However, if limestone is heated, itgoes through a chemical change and produces carbon dioxideand lime, a chemical used in many industrial processes. Thechemical property in this case is the ability to change whenheated.

Another chemical property is the ability to change with elec-trical contact. Electricity can cause a change in some substancesand decompose some compounds. Water is one of those com-pounds that can be broken down with electricity.

Something NewThe important difference in a chemical change is that a

new substance is formed. Because of chemical changes, youcan enjoy many things in life that you would not have experi-enced without them. What about that perfect, browned marsh-mallow you roasted at the bonfire? A chemical changeoccurred as a result of the fire to make the taste and the

appearance different.Sugar is normally a white,

crystalline substance, but afteryou heat it over a flame, itturns to a dark-brown caramel.A new substance has beenformed. Sugar also can under-go a chemical change whensulfuric acid is added to it. Thenew substance is obviously dif-ferent from the original, asshown in Figure 14.

You could not enjoy abirthday cake if the eggs, sugar,flour, baking powder, andother ingredients didn’t changechemically. You would havewhat you see when you pourthe gooey batter into the pan.


Figure 14When sugar and sulfuric acidcombine, a chemical changeoccurs and a new substanceforms. During this reaction, themixture foams and a toxic gas isreleased, leaving only water andair-filled carbon behind. (Becausea toxic gas is released, studentsshould never perform this as anactivity.)

Signs of Change How do you know that you have anew substance? Is it just because it looks different? Youcould put a salad in a blender and it would look differ-ent, but a chemical change would not have occurred.You still would have lettuce, carrots, and any other veg-etables that were there to begin with.

You can look for signs when evaluating whether youhave a new substance as a result of a chemical change.Look at the piece of birthday cake in Figure 15. When acake bakes, gas bubbles form and grow within theingredients. Bubbles are a sign that a chemical changehas taken place. When you look closely at a piece ofcake, you can see the airholes left from the bubbles.

Other signs of change include the production of heat, light,smoke, change in color, and sound. Which of these signs ofchange would you have seen or heard during the campfire?

Is it reversible? One other way to determine whether a phys-ical change or a chemical change has occurred is to decidewhether or not you can reverse the change by simple physicalmeans. Physical changes usually can be reversed easily. Forexample, melted butter can become solid again if it is placed inthe refrigerator. A figure made of modeling clay, like the one inFigure 16, can be smashed to fit back into a container. However,chemical changes can’t be reversed using physical means. Forexample, the ashes in a fireplace cannot be put back together tomake the logs that you had to start with. Can you find the egg ina cake? Where is the white flour?

What kind of change can be reversed easily?


Figure 15The evidence of a chemicalchange in the cake is the holesleft by the air bubbles that wereproduced during baking.

Figure 16A change such as molding clay or changing shape can be undone easily.

Classifying According to Chemical Properties Classify-ing according to physical properties is often easier than classifyingaccording to chemical properties. Table 1 summarizes the twokinds of properties. The physical properties of a substance areeasily observed, but the chemical properties can’t be observedwithout changing the substance. However, once you know thechemical properties, you can classify and identify matter based onthose properties. For example, if you try to burn what looks like apiece of wood but find that it won’t burn, you can rule out thepossibility that it is untreated wood.

In a grocery store, the products sometimes are separatedaccording to their flammability or sensitivity to light or heat.You don’t often see the produce section in front of big windowswhere heat and light come in. The fruit and vegetables wouldundergo a chemical change and ripen too quickly. You alsowon’t find the lighter fluid and rubbing alcohol near the bakeryor other places where heat and flame could be present.

Architects and product designers have to take into accountthe chemical properties of materials when they design buildingsand merchandise. For example, children’s sleepwear and bed-ding can’t be made of a flammable fabric. Also, some of thearchitects designing the most modern buildings are choosingmaterials like titanium because it does not react with oxygen likemany other metals do.

Conservation of MassIt was so convenient to turn the firewood into the small pile

of ash left after the campfire. You began with many kilograms offlammable substances but ended up with just a few kilograms ofash. Could this be a solution to the problems with landfills andgarbage dumps? Why not burn all the trash? If you could makesuch a reduction without creating undesirable materials, thiswould be a great solution.


Observing YeastProcedure1. Observe a tablespoon of

dry yeast with a hand lens.Draw and describe whatyou observe.

2. Put the yeast in 50 mL ofwarm, not hot, water.

3. Compare your observationsof the dry yeast with thoseof the wet yeast.

4. Put a pinch of sugar in the water and observe for15 minutes.

5. Record your observations.

Analysis1. Are new substances formed

when sugar is added to thewater and yeast? Explain.

2. Do you think this is a chemical change or a physical change? Explain.

Table 1 Comparing Properties

Physical Properties color, shape, length, mass, volume, density, state, ability to attracta magnet, melting point, boiling point, malleability, ductility

Chemical Properties flammability; ability to react with: oxygen, electricity, light, water, heat, vinegar, bleach, etc.

Mass Is Not Destroyed Before you celebrate your discov-ery, think this through. Did mass really disappear during the fire?It appears that way when you compare the mass of the pile ofashes to the mass of the firewood you started with. The law ofconservation of mass states that the mass of what you end withis always the same as the mass of what you start with.

This law was first investigated about 200 years ago, and manyinvestigations since then have proven it to be true. One experi-ment done by French scientist Antoine Lavoisier was a small ver-sion of a campfire. He determined that a fire does not make massdisappear or truly get rid of anything. The question, however,remains. Where did the mass go? The ashes aren’t heavy enoughto account for the mass of all of the pieces of firewood.

Where did the mass go? If you look at the campfire exam-ple more closely, you see that the law of conservation of mass istrue. When flammable materials burn, they combine with oxygen.Ash, smoke, and gases are produced. The smoke and gases escapeinto the air. If you could measure the mass of the oxygen and all ofthe original flammable materials that were burned and compare itto the remaining mass of the ash, smoke, and gas, they would beequal.

Identifying the ProblemIn all reactions that occur in the world,

mass is never lost or gained. This is the lawof conservation of mass. An example of thisphenomenon is the light stick. How can youprove this?

Light sticks often are used on Halloweento light the way for trick-or-treaters.

They make children visible to drivers.They also are used as toys, for camping,marking trails, emergency traffic problems,by the military, and they work well under-water. A light stick contains two chemicalsin separate tubes. When you break theinner tube, the two chemicals react pro-ducing a greenish light. The chemicals arenot toxic, and they will not catch fire.

Do light sticks conserve mass?

Solving the ProblemDescribe how you could show that a

light stick does not gain or lose mass whenyou allow the reaction to take place. Is thisreaction a chemical or physical change?What is your evidence?

Problem-Solving Activity


Before and After Mass is not destroyed or created duringany chemical change. The conservation of mass is demonstratedin Figure 17. In the first photo, you see one substance in the flaskand a different substance contained in a test tube inside the flask.The total mass is 16.150 g. In the second photo, the flask is turnedupside down. This allows the two substances to mix and react.Because the flask is sealed, nothing is allowed to escape. In thethird photo, the flask is placed on the balance again and the totalmass is determined to be 16.150 g. If no mass is lost or gained,what happens in a reaction? Instead of disappearing or appearing,the particles in the substances rearrange into different combina-tions with different properties.


Section Assessment

1. What is a chemical property?

2. List four chemical properties.

3. What are some of the signs that a chemicalchange has occurred?

4. Describe the law of conservation of mass.Give an example.

5. Think Critically You see a bright flashand then flames as your teacher performs ademonstration for the class. Is this anexample of a physical change or a chemicalchange? Explain.

6. Comparing and Contrasting Compare and contrast physical change and chemicalchange. For more help, refer to the ScienceSkill Handbook.

7. Solving One-Step Equations A student heats 4.00 g of a blue compound to produce2.56 g of a white compound and an unknownamount of colorless gas. What is the mass of this gas? For more help, refer to the Math Skill Handbook.

Figure 17This reaction demonstrates the conservation of mass.Although a chemical change hasoccurred and new substanceswere made, the mass remainedconstant.

Draw a labeled poster of the substances you placed in your beaker. Research the den-sities of each substance and include thesedensities on your poster. For more help,refer to the Science Skill Handbook.

ACTIVITY 547

Liquid Layers

Allow the glycerin to trickle down the sides ofthe container and observe.

3. Slowly pour 40 mL of water into the beakerand observe.

4. Slowly pour 40 mL of corn oil into the beakerand observe.

5. Slowly pour 40 mL of rubbing alcohol into thebeaker and observe.

6. Carefully drop the penny, hollow plasticsphere, and rubber ball into the beaker andobserve where these items come to a stop.

Conclude and Apply1. In your Science Journal, draw a picture of

the liquids and solids in your flask. Label your diagram.

2. Describe what happened to the five liquidswhen you poured them into the beaker.

3. Infer why the liquids behaved this way.

4. Describe what happened to the three solidsyou placed into the beaker.

5. List the substances you used in your activityin order from those with the highest densityto those with the lowest density.

6. If water has a density of 1 g/cm3, what canyou infer about the densities of the solids andother liquids?

Why must you shake up a bottle of Italiansalad dressing before using it? Have you

observed how the liquids in some dressings sepa-rate into two distinct layers? In this activity, youwill experiment with creating layers of liquids.

What You’ll InvestigateWhat would several liquids and solids of different densities look like when put into thesame container?

Goals■ Create layers of liquids using liquids of

different densities.■ Observe where solids of different densities

will rest in the liquid layers.■ Infer the densities of the different materials.

Materials250-mL beaker corn oilgraduated cylinder rubbing alcoholcorn syrup pennyglycerin hollow plastic spherewater rubber ball

Safety Precautions

Procedure1. Pour 40 mL of corn syrup into your beaker.

2. Slowly pour 40 mL of glycerin into the beaker.

Goals■ Design an experiment that identi-

fies physical changes and chemicalchanges in fruit.

■ Observe whether chemical changescan be controlled.

Possible Materialsbananasapplespearsplastic or glass mixing bowls (2)lemon/water solution (500 mL)paring knife

Safety Precautions

WARNING: Be careful when workingwith sharp objects. Always keep handsaway from sharp blades. Never eat any-thing in the laboratory.

When you are looking forward to enjoying a tasty, sweet fruit salad at a picnic, thelast thing you want to see is brown fruit in the bowl. What can you do about this

problem? Your teacher has given you a few different kinds of fruit. It is your task to per-form a test in which you will observe a physical change and a chemical change.

Recognize the ProblemCan a chemical change be controlled?

Form a HypothesisBased on your reading and observations, state a hypothesis about whether you cancontrol a chemical change.

Fruit Salad Favorites

548 CHAPTER 18

Write a page for an illustrated cookbookexplaining the benefits you found in thisexperiment. Include drawings and a step-by-step procedure. For more help, refer to theScience Skill Handbook.

Test Your Hypothesis

Analyze Your Data

Draw Conclusions

Do1. Ask your teacher to approve your

plan and choice of constants, vari-ables and controls before you start.

2. Perform the investigation as planned.

3. While doing the investigation,record your observations and com-plete the data table you prepared inyour Science Journal.

Plan1. As a group, agree upon the hypoth-

esis and decide how you will test it.Identify what results will confirm thehypothesis.

2. List each of the steps you will needin order to test your hypothesis.Be specific. Describe exactly whatyou will do in each step. List all ofyour materials.

3. Prepare a data table in your ScienceJournal or on a computer for yourobservations.

4. Read the entire investigation to makesure all steps are in logical order.

5. Identify all constants, variables,and controls of the investigation.

4. What are your variables?

5. Did you encounter any problems carrying out the investigation?

6. Do you have any suggestions for changes in a future investigation?

1. Compare and contrast thechanges you observe in the controland the test fruit.

2. Compare your results with those ofother groups.

3. What was your control in this investigation?

1. Did the results support your hypothesis? Explain.

2. Describe what effect refrigerating thetwo salads would have on the fruit.

3. What will you do with the fruit from thisexperiment? Could it be eaten?

ACTIVITY 549

Section 1 Physical Properties and Changes

1. Any characteristic of a material that can beobserved or measured is a physical prop-erty. What can you observe or measure aboutthe baby in the photo?

2. The four states of matter are solid, liquid,gas, and plasma. The state of matter is aphysical property that is dependent on tem-perature and pressure.

3. State, color, shape, length, mass, volume,attraction by a magnet, density, meltingpoint, boiling point, luster, malleability, andductility are common physical properties.

4. In a physical change the properties of a sub-stance change but the identity of the sub-stance always stays the same.

5. You can classify materials according to theirphysical properties. What different physicalproperties could you use to classify the objectsin the photo?

550 CHAPTER STUDY GUIDE

Section 2 Chemical Properties and Changes

1. Chemical properties give asubstance the ability toundergo a chemical change.What chemical property isbeing displayed in the photo?

2. Common chemical propertiesinclude: ability to burn, reactswith oxygen, reacts with heat or light, andbreaks down with electricity.

3. In a chemical change substances combine toform a new material. Is the balloon about toundergo a chemical or physical change?

4. The mass of the products of a chemicalchange is always the same as the mass ofwhat you started with.

5. A chemical change results in a substancewith a new identity, but matter is not created or destroyed.

Use the information inyour Foldable to compareand contrast physical and

chemical properties of matter. Write abouteach on the back of the tabs.

After You ReadFOLDABLESReading & StudySkills

FOLDABLESReading & Study Skills

Study GuideChapter 1818

Vocabulary Wordsa. boiling point f. matterb. chemical change g. melting pointc. chemical property h. physical changed. conservation i. physical property

of mass j. states of mattere. density

Using VocabularyThe sentences below include terms that have

been used incorrectly. Change the incorrect termsso the sentence reads correctly.

1. The boiling point is the temperature at whichmatter in a solid state changes to a liquid.

2. Matter is a measure of the mass of an objectin a given volume.

3. A chemical change is easily observed ormeasured without changing the object.

4. Physical changes result in a new substanceand cannot be reversed by physical means.

5. The four states of matter are solid, volume,liquid, and melting point.

Make a study schedule for yourself. If you have aplanner, write down exactly which hours you planto spend studying and stick to it.

Study Tip

Complete the following table comparing properties of different objects.

CHAPTER STUDY GUIDE 551

Type of Matter Physical Properties Chemical Properties

log

pillow

bowl of cookie dough

book

glass of orange juice

Properties of Matter

flammability

flammability

reacts with heat

flammability

reacts with bleach

brown, round, might have length, solid

soft, might describe color, size, solid

color, gooey, chunks in it, solid

might describe size, rectangle, color, solid

might describe volume, liquid, color

Study GuideChapter 1818

Choose the word or phrase that best answersthe question.

1. What statement describes the physicalproperty of density?A) the distance between two points B) how light is reflected from an object’s

surfaceC) the amount of mass for a given volumeD) the amount of space an object takes up

2. Which of the following is an example of aphysical change?A) tarnishing C) burningB) rusting D) melting

3. Which of the choices below describes a boiling point?A) a chemical propertyB) a chemical changeC) a physical propertyD) a color change

4. Which of the following is a sign that achemical change has occurred?A) smoke C) change in shapeB) broken pieces D) change in state

5. Which describes what volume is?A) the area of a squareB) the amount of space an object takes upC) the distance between two pointsD) the temperature at which boiling begins

6. What property is described by the ability ofmetals to be hammered into sheets?A) mass C) volumeB) density D) malleability

7. Which of these is a chemical property?A) sizeB) densityC) flammabilityD) volume

8. When iron reacts with oxygen, what substance is produced?A) tarnishB) rustC) patinaD) ashes

9. What kind of change results in a newsubstance being produced?A) chemical C) physicalB) mass D) change of state

10. What is conserved during any change?A) color C) identityB) volume D) mass

11. Use the law of conservation of matter toexplain what happens to atoms when theycombine to form a new substance.

12. Describe the four states of matter. How arethey different?

13. A globe is placed onyour desk and you areasked to identify itsphysical properties.How would youdescribe the globe?

14. What information doyou need to knowabout a material tofind its density?

15. Classifying Classify the following as achemical or physical change: an egg breaks,a newspaper burns in the fireplace, a dish ofice cream is left out and melts, and a loaf ofbread is baked.

552 CHAPTER ASSESSMENT

AssessmentChapter 1818

CHAPTER ASSESSMENT 553

16. Measuring in SI Find the density of thepiece of lead that has a mass of 49.01 g anda volume of 4.5 mL.

17. Concept Mapping Use the spider-mappingskill to organize and define physical proper-ties of matter. Include the concepts of color,shape, length, density, mass, states of mat-ter, volume, density, melting point, andboiling point.

18. Making and Using Tables Complete thetable by supplying the missing information.

19. Drawing Conclusions List the physical andchemical properties and changes thatdescribe the process of scrambling eggs.

20. Comic Strip Create a comic strip demon-strating a chemical change in a substance.Include captions and drawings that demon-strate your understanding of conservationof matter.

Unknown matter can be identified bytaking a sample of it and comparing itsphysical properties to those of already iden-tified substances.

Study the table and answer the follow-ing questions.

1. A scientist has a sample of a substancewith a density greater than 1 g/mL.According to the table, which of thesesubstances has a density greater than 1 g/mL?A) gasolineB) waterC) aluminumD) methane

2. A physical change occurs when theform or appearance of a substance is changed. All of the following are examples of physical changesEXCEPT _____.F) the vaporization of gasoline G) corrosion of aluminumH) methane diluted by airJ) water freezing into ice

Test Practice

Type Definition Examples

solid books, desk, chair, ice cubes

liquid Particles do not stay in one position.They move past each other.

gas oxygen, helium, vapor

States of Matter

Substance

Physical Properties

Gasoline

Aluminum

Methane

Water

0.703

2.700

0.466

1.000

Clear

Silver

Colorless

Clear

Density(g/ml)

Color

Go to the Glencoe Science Web site at science.glencoe.com or use theGlencoe Science CD-ROM for additionalchapter assessment.

TECHNOLOGY

Particles vibrate in afixed position.

Particles move freelywith energy. Theymove all around.

water, juice, tea,soft drink, etc.

AssessmentChapter 1818


Unit 6 Science (Glencoe Red 2002)

Education

Transcript of Unit 6 Science (Glencoe Red 2002)