Unit 6 Science (Glencoe Red 2002)


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Unit 6 Science (Glencoe Red 2002)

  1. 1. 6 Matter, Forces,UNIT and Energy How Are Train Schedules & Oil Pumps Connected?524
  2. 2. I n 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, aworker 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! SCIENCE CONNECTION FRICTION AND LUBRICANTS A lubricant is a substance that reduces friction between surfaces that touch one another. Some of the world’s first lubricants were animal and plant products such as lard and vegetable oils. Conduct research to identify a variety of modern-day lubricants. Select one lubricant you learned about and create a poster that shows its source, how it is made or processed, its special properties, and how it is used to reduce friction.
  3. 3. 18 Properties and Changes of MatterW endy Craig Duncan car- ried the Olympic flame underwater on the way tothe 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 yourScience Journal.526
  4. 4. EXPLORE Y our teacher has given you a collection of pennies. It is your task to separate these pennies into ACTIVITY groups while using words to describe each set. In this chapter, you will learn how to identify things based on their physical and chemical properties. With an understanding of these principles of matter, you will discover how things are classified or put into groups. Classify coins 1. Observe the collection of pennies. 2. Choose a characteristic that will allow you to separate the pennies into 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. Observe Think about how your group classified its pennies. Describe the system your group used in your Science Journal.FOLDABLESReading & Study Making an Organizational Study Fold Make the followingSkills Foldable to help you organize your thoughts into clear categories about properties of matter. Physical Chemical Properties Properties1. 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 into al Chemic fourths. Fold the paper in half from top to bottom. Unfold. Physics a Chang l e Chang es3. Through the top thickness of paper, cut along both of the middle fold lines to form four tabs. Label the tabs Physical Properties, Physical Changes, 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. 527
  5. 5. SECTION Physical Properties and Changes Using Your Senses As you look in your empty wallet and realize that yours Identify physical properties allowance isn’t coming anytime soon, you decide to get an after- of matter. school job. You’ve been hired at the new grocery store that wills Describe the states of matter. open next month. They are getting everything ready for thes Classify matter using physical grand opening, and you will be helping make decisions about properties. where things will go and how they will be arranged.Vocabulary When you come into a new situation or have to make anyphysical property state of matter kind of decision, what do you usually do first? Most peoplematter melting pointphysical change boiling point would make some observations. Observing involves seeing,density hearing, tasting, touching, and smelling. Whether in a new job or in the laboratory, you use your senses to observe materials. Any characteristic of a material thatObserving physical properties can be observed or measured without changing the identity ofwill help you interpret the world the material is a physical property. However, it is important toaround you. never taste, touch, or smell any of the materials being used in the lab without guidance, as noted in Figure 1. For safety reasons you will rely mostly on other observations. Watch ListenFigure 1For safety reasons, in Do NOTthe laboratory you touchusually use only twoof your senses—sightand hearing. Many Do NOT smellchemicals can be dan-gerous to touch,taste, and smell. Do NOT taste528
  6. 6. Figure 2 The identity of the material does not necessarily depend on its color. Each of these bottles is made of high-density polyethylene (HDPE).Physical Properties On the first day of your new job, the boss gives you aninventory 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, it Research Visit thechanges shape. However, the material is still plastic. This type of Glencoe Science Web site atchange is called a physical change. It is important to realize that science.glencoe.comin a physical change, the physical properties of a substance for more information aboutchange, but the identity of the substance does not change. classifying matter by its phys-Notice Figure 2. The detergent bottles are made of high-density ical properties. Communicatepolyethylene regardless of the differences in the physical proper- to your class what you learn.ties of color or shape. What is matter? SECTION 1 Physical Properties and Changes 529
  7. 7. 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 bread in the bakery section of your store by the length of the loaf. But, even though the dough has been shaped in different lengths, it is still French bread. Back in the laundry aisle, you notice a child struggling to lift one of the boxes of detergent. That raises a question. How much Collect Data Visit the detergent is in each box? Mass is a physical property that Glencoe Science Web site at describes the amount of material in an object. Some of the science.glencoe.com for boxes are heavy, but, the formula of the detergent hasn’t information about density. changed from the small box to the large box. Organizing the Communicate to your class boxes by mass is another option. what you learn. Volume and Density Mass isn’t the only physical property that describes how much of something you have. Another measurement is volume. Volume measures the amount of space an object takes up. Liquids usually are measured by volume. The juice bottles on your list could be organized by volume. Another measurable physical property related to mass and volume is density—the amount of mass a material has for a given volume. You notice this property when you try to lift twoFigure 3 things of equal volume that have different masses. Density isThe length of any object found by dividing the mass of an object by its volume.can be measured with the density ϭ massրvolume, or D ϭ mրVappropriate tool.530 CHAPTER 18 Properties and Changes of Matter
  8. 8. Figure 4 These balls take up about the same space, but the bowling ball on the left has more mass than the kickball on the right. Therefore, the bowling ball is more dense. Bowling ball KickballSame 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 kept Changing Densityin the freezer at 0°C is in the form of ice. The density of that ice is Procedure0.9168 g/cm3. Has the identity of water changed? No, but some- 1. Stir three tablespoons ofthing has changed. baking soda in 3/4 cup of warm water. Set aside. What two measurements are related in the 2. Pour vinegar into a clear measurement of density? glass until it is half full. 3. Slowly pour the baking soda and warm water mixtureStates of Matter into the glass of vinegar. What changes when water goes from 20°C to 0°C? It 4. After most of the fizzing has stopped, place three halveschanges from a liquid to a solid. The four states of matter are of raisins in the glass.solid, liquid, gas, and plasma (PLAZ muh). The state of mat- 5. Record your observations inter of a substance depends on its temperature and pressure. your Science Journal or on aThree of these states of matter are things you talk about or computer.experience every day, but the term plasma might be unfamil- Analysisiar. The plasma state occurs at very high temperatures and is 1. How did the bubbles affectfound in fluorescent (floo RE sunt) lightbulbs, the atmo- the raisins?sphere, and in lightning strikes. 2. Infer what changed the As you look at the products to shelve in your grocery store, density of the raisins.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. SECTION 1 Physical Properties and Changes 531
  9. 9. 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 shape and volume. The particles of a liquid are moving much faster and have enough energy to slide past one another. This allows a liquid to take the shape of its container. The particles of a gas are moving so quickly that they have enough energy to move freely away from other particles. The particles of a gas take up as much space 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 the shape of the container?Figure 5Water can be in three different Changes of State You witness a change of state when youstates: solid, liquid, and gas. The put ice cubes in water and they melt. You still have water but inmolecules in a solid are tightlypacked and vibrate in place, but another form. The opposite physical change happens when youin a liquid they can slip past each put liquid water in ice-cube trays and pop them in your freezer.other because they have more The water doesn’t change identity—only the state it is in.energy to move. In a gas, they For your job, you will need to make some decisions based onmove freely all around the con- the ability of materials to change state. You don’t want all thosetainer with even more energy. frozen items thawing out and becoming slushy liquid. You also don’t want some of the liquids to get so cold that they freeze. Solid water Liquid water Gaseous water532 CHAPTER 18 Properties and Changes of Matter
  10. 10. Melting and Boiling Points Atwhat temperature will water in the Liquid nitrogenform of ice change into a liquid? The (below –195.8°C)temperature at which a solid becomesa liquid is its melting point. The Nitrogen gasmelting point of a pure substance (above –195.8°C)does 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 state Figure 6becomes a gas. Each pure substance has a unique boiling point at When liquid nitrogen is pouredatmospheric pressure. The boiling point of water is 100°C at from a flask, you see an instantatmospheric pressure. The boiling point of nitrogen is Ϫ195.8°C, change to gas because nitrogen’sso it changes to a gas when it warms after being spilled into the boiling point is –195.8°C, whichopen air, as shown in Figure 6. The boiling point, like the melting is much lower than roompoint, does not depend on the amount of the substance. temperature. 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 at When geologists describe100°C. If you know the boiling points and melting points of sub- rocks, they use specificstances, you can classify substances based on those points. terms that have meaning to all other scientists whoMetallic Properties read their descriptions. To describe the appearance of Other physical properties allow you to classify substances as a rock or mineral, they usemetals. You already have seen how you can classify things as the following terms: metal-solids, liquids, or gases or according to color, shape, length, lic, adamantine, vitreous,mass, volume, or density. What properties do metals have? resinous, pearly, silky, and greasy. Research these terms and write a defini-How do metals look and act? Often the first thing you tion and example of each innotice about something that is a metal is its shiny appearance. your Science Journal.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. SECTION 1 Physical Properties and Changes 533
  11. 11. Figure 7This artist has taken advantageof the ductility of metal bychoosing wire as the mediumfor her sculpture. Uses of Metals Metals can be used in unique ways because of some of the physical properties they have. For example, many metals can be hammered, pressed, or rolled into thin sheets. This property of metals is called malleability (mal lee uh BIH luh tee). The malleability of copper makes it an ideal choice for artwork such as the Statue of Liberty. Many metals can be drawn into wires as shown in Figure 7. This property is called ductility (duk TIH luh tee). The wires in buildings and most electrical equipment and household appliances are made from copper. Sil- ver and platinum are also ductile. You probably observe another physical property of some metals every day when you go to the refrigerator to get milk or juice for breakfast. Your refrigerator door is made of metal.Figure 8 Some metals respond to magnets. Most people make use of thatThis junkyard magnet pulls scrap property and put reminder notes, artwork, and photos on theirmetal that can be salvaged from refrigerators. Some metals have groups of atoms that can bethe rest of the debris. It is sorting affected by the force of a magnet, and they are attracted to theby a physical property. magnet 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 grocery carts and thinks about shelving. Mal- leable carts can be dented. How could the shelf ’s attraction of magnets be used to post advertisements or weekly specials? Perhaps the prices could be fixed to the shelves with magnetic numbers. After you observe the physi- cal properties of an object, you can make use of those properties.534 CHAPTER 18 Properties and Changes of Matter
  12. 12. 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- Figure 9ture. You can measure the mass, volume, and density of a Coins can be sorted by their phys-sample of salt or find out if it would attract a magnet. These ical properties. Sorting by size isare examples of how physical properties can be used to iden- used here.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 use physical properties or characteristics to 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. SECTION 1 Physical Properties and Changes 535
  13. 13. VISUALIZING DICHOTOMOUS KEYSFigure 10 hether in the laboratory orW in the field, scientists often encounter substancesor organisms that they cannot imme- Dichotomous Key 1. A. Lives in a “borrowed” shelldiately identify. One approach to (usually some type of snail shell) Hermit Crabtracking down the identity of such B. Does not live in a “borrowed” shell go to #2“unknowns” is to use a dichotomouskey, such as the one shown. The key is 2. A. Shell completely overlapsdesigned so a user can compare physi- the walking legs Box Crabcal properties or characteristics of the B. Walking legs are exposed Kelp Crabunknown substance or organism—inthis case, a crab—with characteristicsof known organisms in a stepwisemanner. With each step, a choice Can you identify themust be made. Each choice leads to three crabs shown heresubsequent steps that guide the user by following thisthrough the key until a positive identi- dichotomous key?fication is made.536 CHAPTER 18
  14. 14. 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, Figure 11medium-sized dog with large black spots on his back. He also Physical descriptions are usedhas black ears and a black mask around his eyes. The manager of to determine the identities ofthe shelter tells you that the dog is close to full-grown. What unknown things. What physicalbreed is the dog? properties are used to describe this 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 is unknown 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.Substances Oxygen Matter—everything that has mass and takes up space—canbe 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- Goldpounds.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- Aluminumminum foil is made up of only aluminum atoms. Elements can- Figure 12not be broken down into simpler substances by physical or Elements such as oxygen, gold,chemical means. However, different elements can combine to and aluminum are made up ofform new substances—called compounds. only one type of atom. SECTION 1 Physical Properties and Changes 537
  15. 15. Oxygen atom H O H Hydrogen atoms H2O Compounds What do you call the colorless liquid that flows from the kitchen faucet? You probably call it water, but maybeFigure 13 you’ve seen it written as H2O. The elements hydrogen and oxy-Compounds contain more than gen exist separately as colorless gases. However, these two ele-one type of atom bonded ments can combine to form the compound water, shown intogether.Water contains a ratio Figure 13, with properties that are different from the individualof two hydrogen atoms bonded gases that make it up. A compound is a substance that is madeto one oxygen atom. up of atoms of more than one element chemically bonded together. The smallest unit of water is made up of two hydrogen atoms and one oxygen atom bonded together. Compounds have a fixed ratio—or proportion of atoms throughout. For example, every drop of water contains a ratio of two hydrogen atoms to one oxygen atom. Every sample of car- bon dioxide contains a ratio of one carbon atom to two oxygen atoms. Compounds can be broken down only by chemical means into 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 is added to water, it can be broken down into hydrogen gas and oxygen gas. Mixtures When 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 the identity of the mixture. For example, if you put some sand into a bucket of water, the sand doesn’t chemically combine with the water. If you add more sand or more water, it’s still a mixture of sand 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.538 CHAPTER 18 Properties and Changes of Matter
  16. 16. 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 include Figure 14salad, a bookshelf full of books, or a toolbox full of nuts and The salad and the pizza are het-bolts. Figure 14 shows examples of heterogeneous and homoge- erogeneous mixtures.The fruitneous mixtures. drink is a homogeneous mixture. Section Assessment 1. What property of matter is used to mea- sure the amount of space an object takes? 6. Concept Mapping Using a computer, draw a 2. What are the four states of matter? cycle concept map with the steps for changing Describe each and give an example. an ice cube into steam. Use the terms melting 3. How might a substance such as water have point and boiling point in your answer. For more two different densities? help, refer to the Science Skill Handbook. 4. Compare and contrast heterogeneous and 7. Solving One-Step Equations Calculate the homogeneous mixtures. volume of an object that has a length of 10 cm, 5. Think Critically Explain why the boiling a width of 10 cm, and a height of 10 cm. Use point is the same for 1 L and 3 L of water. the formula for volume: V ϭ lwh. Express your Will it take the same amount of time for answer using cubic centimeters (cm3). For more each volume of water to begin to boil? help, refer to the Math Skill Handbook. SECTION 1 Physical Properties and Changes 539
  17. 17. SECTION Chemical Properties and Changes Ability to Change It is time to celebrate. You and your coworkers have cooper-s Recognize chemical properties. ated in classifying all of the products and setting up the shelvess Identify chemical changes. in the new grocery store. The store manager agrees to a celebra-s Classify matter according to tion party and campfire at the nearby park. Several large pieces chemical properties. of firewood and some small pieces of kindling are needed tos Describe the law of conservation of mass. start the campfire. After the campfire, all that remains of the wood is a small pile of ash. Where did the wood go? What prop-Vocabulary erty of the wood is responsible for this change?chemical propertychemical change All of the properties that you observed and used for classifi-conservation of mass cation in the first section were physical properties that you could observe easily. In addition, even when those properties changed, the identity of the object remained the same. Some-Knowing the chemical properties will thing different seems to have happened in the bonfire example.allow you to distinguish differences Some properties do indicate a change of identity for the sub-in matter. stances involved. A chemical property is any characteristic that gives a substance the ability to undergo a change that results in a new substance. Figure 12 shows some properties of substances that can be observed only as they undergo a chemical change.Figure 12These are four examples of What does a chemical property give a substancechemical properties. the ability to do?Flammability Reacts with oxygen Reacts with light Reacts with water540 CHAPTER 18 Properties and Changes of Matter
  18. 18. Common Chemical Properties Figure 13 Many kinds of interactions You don’t have to be in a laboratory to see changes that take with oxygen can occur.place because of chemical properties. These are called chemical An untreated iron gate willchanges. A chemical change is a change in the identity of a sub- rust. Silver dishes developstance due to the chemical properties of that substance. A new tarnish. Copper sculpturessubstance or substances are formed in such a change. develop a green patina, which is The campfire you enjoyed to celebrate the opening of the gro- a mixture of copper compounds.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 chemical Researchers have discov-property of inflammability. ered an enzyme in fruit that is involved in theCommon Reactions An unpainted iron gate, such as the browning process. Theyone shown in Figure 13A, will rust in time. The rust is a result of are doing experiments tooxygen in the air reacting with the iron and causing corrosion. try to grow grapevines in which the level of thisThe corrosion produces a new substance called iron oxide. enzyme, polyphenol oxi-Other chemical reactions occur when metals interact with dase (PPO), is reduced.other elements. Figure 13B shows tarnish, the grayish-brown This could result infilm that develops on silver when it reacts with sulfur in the air. grapes that do not brownThe ability to react with oxygen or sulfur is a chemical property. as quickly. Write a para-Figure 13C shows another example of this chemical property. graph in your Science Have you ever sliced an apple or banana and left it sitting Journal about why this would be helpful to fruiton the table? The brownish coloring that you notice is a chem- growers, store owners,ical change that occurs between the fruit and the oxygen in the and customers.air. 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
  19. 19. Heat and Light Vitamins often are dispensed in dark-brown bottles. Do you know why? Many vitamins have the ability to change when exposed to light. This is a chemical property. They are 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, it goes through a chemical change and produces carbon dioxide and lime, a chemical used in many industrial processes. The chemical property in this case is the ability to change when heated. Another chemical property is the ability to change with elec- trical contact. Electricity can cause a change in some substancesFigure 14 and decompose some compounds. Water is one of those com-When sugar and sulfuric acid pounds that can be broken down with electricity.combine, a chemical changeoccurs and a new substanceforms. During this reaction, the Something Newmixture foams and a toxic gas is The important difference in a chemical change is that areleased, leaving only water and new substance is formed. Because of chemical changes, youair-filled carbon behind. (Because can enjoy many things in life that you would not have experi-a toxic gas is released, students enced without them. What about that perfect, browned marsh-should never perform this as an mallow you roasted at the bonfire? A chemical changeactivity.) occurred as a result of the fire to make the taste and the appearance different. Sugar is normally a white, crystalline substance, but after you heat it over a flame, it turns to a dark-brown caramel. A new substance has been formed. Sugar also can under- go a chemical change when sulfuric acid is added to it. The new substance is obviously dif- ferent from the original, as shown in Figure 14. You could not enjoy a birthday cake if the eggs, sugar, flour, baking powder, and other ingredients didn’t change chemically. You would have what you see when you pour the gooey batter into the pan.542 CHAPTER 18 Properties and Changes of Matter
  20. 20. 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. Figure 15 Other signs of change include the production of heat, light, The evidence of a chemicalsmoke, change in color, and sound. Which of these signs of change in the cake is the holeschange would you have seen or heard during the campfire? left by the air bubbles that were produced during baking.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 to Figure 16make the logs that you had to start with. Can you find the egg in A change such as molding claya cake? Where is the white flour? or changing shape can be undone easily. What kind of change can be reversed easily? SECTION 2 Chemical Properties and Changes 543
  21. 21. Table 1 Comparing Properties Physical Properties color, shape, length, mass, volume, density, state, ability to attract a magnet, melting point, boiling point, malleability, ductility Chemical Properties flammability; ability to react with: oxygen, electricity, light, water, heat, vinegar, bleach, etc. Classifying According to Chemical Properties Classify- ing according to physical properties is often easier than classifying according to chemical properties. Table 1 summarizes the two kinds of properties. The physical properties of a substance are easily observed, but the chemical properties can’t be observed without changing the substance. However, once you know the chemical properties, you can classify and identify matter based on those properties. For example, if you try to burn what looks like aObserving Yeast piece of wood but find that it won’t burn, you can rule out theProcedure possibility that it is untreated wood.1. Observe a tablespoon of In a grocery store, the products sometimes are separated dry yeast with a hand lens. according to their flammability or sensitivity to light or heat. Draw and describe what You don’t often see the produce section in front of big windows you observe. where heat and light come in. The fruit and vegetables would2. Put the yeast in 50 mL of warm, not hot, water. undergo a chemical change and ripen too quickly. You also3. Compare your observations won’t find the lighter fluid and rubbing alcohol near the bakery of the dry yeast with those or other places where heat and flame could be present. of the wet yeast. Architects and product designers have to take into account4. Put a pinch of sugar in the chemical properties of materials when they design buildings the water and observe for and merchandise. For example, children’s sleepwear and bed- 15 minutes.5. Record your observations. ding can’t be made of a flammable fabric. Also, some of the architects designing the most modern buildings are choosingAnalysis materials like titanium because it does not react with oxygen like1. Are new substances formed when sugar is added to the many other metals do. water and yeast? Explain.2. Do you think this is a chemical change or a Conservation of Mass physical change? Explain. It was so convenient to turn the firewood into the small pile of ash left after the campfire. You began with many kilograms of flammable substances but ended up with just a few kilograms of ash. Could this be a solution to the problems with landfills and garbage dumps? Why not burn all the trash? If you could make such a reduction without creating undesirable materials, this would be a great solution.544 CHAPTER 18 Properties and Changes of Matter
  22. 22. 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. Problem-Solving Activity Do light sticks conserve mass? ight sticks often are used on Halloween L to 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 chemicals in separate tubes. When you break the inner tube, the two chemicals react pro- ducing a greenish light. The chemicals are not toxic, and they will not catch fire. Identifying the Problem Solving the Problem In all reactions that occur in the world, Describe how you could show that a mass is never lost or gained. This is the law light stick does not gain or lose mass when of conservation of mass. An example of this you allow the reaction to take place. Is this phenomenon is the light stick. How can you reaction a chemical or physical change? prove this? What is your evidence? SECTION 2 Chemical Properties and Changes 545
  23. 23. Figure 17 Before and After Mass is not destroyed or created duringThis reaction demonstrates any chemical change. The conservation of mass is demonstratedthe conservation of mass. in Figure 17. In the first photo, you see one substance in the flaskAlthough a chemical change has and a different substance contained in a test tube inside the flask.occurred and new substances The total mass is 16.150 g. In the second photo, the flask is turnedwere made, the mass remained upside down. This allows the two substances to mix and react.constant. Because the flask is sealed, nothing is allowed to escape. In the third photo, the flask is placed on the balance again and the total mass 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. 6. Comparing and Contrasting Compare 3. What are some of the signs that a chemical and contrast physical change and chemical change has occurred? change. For more help, refer to the Science 4. Describe the law of conservation of mass. Skill Handbook. Give an example. 7. Solving One-Step Equations A student 5. Think Critically You see a bright flash heats 4.00 g of a blue compound to produce and then flames as your teacher performs a 2.56 g of a white compound and an unknown demonstration for the class. Is this an amount of colorless gas. What is the mass of example of a physical change or a chemical this gas? For more help, refer to the Math change? Explain. Skill Handbook.546 CHAPTER 18 Properties and Changes of Matter
  24. 24. Liquid Layers Allow the glycerin to trickle down the sides ofW hy must you shake up a bottle of Italian salad dressing before using it? Have youobserved how the liquids in some dressings sepa- the container and observe. 3. Slowly pour 40 mL of water into the beakerrate into two distinct layers? In this activity, you and observe.will experiment with creating layers of liquids. 4. Slowly pour 40 mL of corn oil into the beakerWhat You’ll Investigate and observe.What would several liquids and solids of 5. Slowly pour 40 mL of rubbing alcohol into thedifferent densities look like when put into the beaker and observe.same container? 6. Carefully drop the penny, hollow plastic sphere, and rubber ball into the beaker andGoals observe where these items come to a stop.s Create layers of liquids using liquids of different densities.s Observe where solids of different densities Conclude and Apply will rest in the liquid layers. 1. In your Science Journal, draw a picture ofs Infer the densities of the different materials. the liquids and solids in your flask. Label your diagram.Materials250-mL beaker corn oil 2. Describe what happened to the five liquidsgraduated cylinder rubbing alcohol when you poured them into the beaker.corn syrup penny 3. Infer why the liquids behaved this way.glycerin hollow plastic sphere 4. Describe what happened to the three solidswater rubber ball you placed into the beaker. 5. List the substances you used in your activity in order from those with the highest density to those with the lowest density. 6. If water has a density of 1 g/cm3, what can you infer about the densities of the solids and other liquids?Safety Precautions Draw a labeled poster of the substances you placed in your beaker. Research the den- Procedure sities of each substance and include these densities on your poster. For more help, 1. Pour 40 mL of corn syrup into your beaker. refer to the Science Skill Handbook. 2. Slowly pour 40 mL of glycerin into the beaker. ACTIVITY 547
  25. 25. Fruit Salad Favorites W hen you are looking forward to enjoying a tasty, sweet fruit salad at a picnic, the last 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 Problem Can a chemical change be controlled? Form a Hypothesis Based on your reading and observations, state a hypothesis about whether you can control a chemical change. Goals Possible Materials s Design an experiment that identi- bananas fies physical changes and chemical apples changes in fruit. pears s Observe whether chemical changes plastic or glass mixing bowls (2) can be controlled. lemon/water solution (500 mL) paring knife Safety Precautions WARNING: Be careful when working with sharp objects. Always keep hands away from sharp blades. Never eat any- thing in the laboratory.548 CHAPTER 18
  26. 26. Test Your HypothesisPlan Do1. As a group, agree upon the hypoth- 1. Ask your teacher to approve your esis and decide how you will test it. plan and choice of constants, vari- Identify what results will confirm the ables and controls before you start. hypothesis. 2. Perform the investigation as planned.2. List each of the steps you will need 3. While doing the investigation, in order to test your hypothesis. record your observations and com- Be specific. Describe exactly what plete the data table you prepared in you will do in each step. List all of your Science Journal. your materials.3. Prepare a data table in your Science Journal or on a computer for your observations.4. Read the entire investigation to make sure all steps are in logical order.5. Identify all constants, variables, and controls of the investigation. Analyze Your Data1. Compare and contrast the 4. What are your variables? changes you observe in the control 5. Did you encounter any and the test fruit. problems carrying out the2. Compare your results with those of investigation? other groups. 6. Do you have any suggestions3. What was your control in this for changes in a future investigation? investigation? Draw Conclusions1. Did the results support your hypothesis? Explain. Write a page for an illustrated cookbook2. Describe what effect refrigerating the explaining the benefits you found in this two salads would have on the fruit. experiment. Include drawings and a step-by-3. What will you do with the fruit from this step procedure. For more help, refer to the experiment? Could it be eaten? Science Skill Handbook. ACTIVITY 549
  27. 27. Chapter 18 Study GuideSection 1 Physical Properties Section 2 Chemical Propertiesand Changes and Changes1. Any characteristic of a material that can be 1. Chemical properties give a observed or measured is a physical prop- substance the ability to erty. What can you observe or measure about undergo a chemical change. the baby in the photo? What chemical property is being displayed in the photo? 2. Common chemical properties include: ability to burn, reacts with oxygen, reacts with heat or light, and breaks down with electricity. 3. In a chemical change substances combine to form a new material. Is the balloon about to undergo a chemical or physical change?2. The four states of matter are solid, liquid, gas, and plasma. The state of matter is a physical property that is dependent on tem- perature and pressure.3. State, color, shape, length, mass, volume, attraction by a magnet, density, melting point, boiling point, luster, malleability, and ductility are common physical properties.4. In a physical change the properties of a sub- 4. The mass of the products of a chemical stance change but the identity of the sub- change is always the same as the mass of stance always stays the same. what you started with.5. You can classify materials according to their 5. A chemical change results in a substance physical properties. What different physical with a new identity, but matter is not properties could you use to classify the objects created or destroyed. in the photo? After You Read FOLDABLES Reading &Study & Study Use the information in Skills your Foldable to compare and contrast physical and chemical properties of matter. Write about each on the back of the tabs.550 CHAPTER STUDY GUIDE
  28. 28. Chapter 18 Study GuideComplete the following table comparing properties of different objects. Properties of Matter Type of Matter Physical Properties Chemical Properties log brown, round, might have length, solid flammability pillow soft, might describe color, size, solid flammability bowl of cookie dough color, gooey, chunks in it, solid reacts with heat book might describe size, rectangle, color, solid flammability glass of orange juice might describe volume, liquid, color reacts with bleachVocabulary Words Using Vocabularya. boiling point f. matter The sentences below include terms that haveb. chemical change g. melting point been used incorrectly. Change the incorrect termsc. chemical property h. physical change so the sentence reads correctly.d. conservation i. physical property 1. The boiling point is the temperature at which of mass j. states of matter matter in a solid state changes to a liquid.e. density 2. Matter is a measure of the mass of an object in a given volume. 3. A chemical change is easily observed or Study Tip measured without changing the object. 4. Physical changes result in a new substance Make a study schedule for yourself. If you have a and cannot be reversed by physical means. planner, write down exactly which hours you plan to spend studying and stick to it. 5. The four states of matter are solid, volume, liquid, and melting point. CHAPTER STUDY GUIDE 551
  29. 29. Chapter 18 Assessment 8. When iron reacts with oxygen, what substance is produced? Choose the word or phrase that best answers A) tarnishthe question. B) rust 1. What statement describes the physical C) patina property of density? D) ashes A) the distance between two points 9. What kind of change results in a new B) how light is reflected from an object’s substance being produced? surface A) chemical C) physical C) the amount of mass for a given volume B) mass D) change of state D) the amount of space an object takes up 10. What is conserved during any change? 2. Which of the following is an example of a A) color C) identity physical change? B) volume D) mass A) tarnishing C) burning B) rusting D) melting 3. Which of the choices below describes a boiling point? 11. Use the law of conservation of matter to A) a chemical property explain what happens to atoms when they B) a chemical change combine to form a new substance. C) a physical property 12. Describe the four states of matter. How are D) a color change they different? 4. Which of the following is a sign that a 13. A globe is placed on chemical change has occurred? your desk and you are A) smoke C) change in shape asked to identify its B) broken pieces D) change in state physical properties. 5. Which describes what volume is? How would you A) the area of a square describe the globe? B) the amount of space an object takes up 14. What information do C) the distance between two points you need to know D) the temperature at which boiling begins about a material to 6. What property is described by the ability of find its density? metals to be hammered into sheets? A) mass C) volume B) density D) malleability 7. Which of these is a chemical property? 15. Classifying Classify the following as a A) size chemical or physical change: an egg breaks, B) density a newspaper burns in the fireplace, a dish of C) flammability ice cream is left out and melts, and a loaf of D) volume bread is baked.552 CHAPTER ASSESSMENT
  30. 30. Chapter 18 Assessment16. Measuring in SI Find the density of the piece of lead that has a mass of 49.01 g and Test Practice a volume of 4.5 mL. Unknown matter can be identified by17. Concept Mapping Use the spider-mapping taking a sample of it and comparing its skill to organize and define physical proper- physical properties to those of already iden- ties of matter. Include the concepts of color, tified substances. shape, length, density, mass, states of mat- ter, volume, density, melting point, and Physical Properties boiling point. Density18. Making and Using Tables Complete the Substance Color (g/ml) table by supplying the missing information. Gasoline 0.703 Clear States of Matter Type Definition Examples Aluminum 2.700 Silver solid Particles vibrate in a books, desk, fixed position. chair, ice cubes Methane 0.466 Colorless liquid Particles do not water, juice, tea, stay in one position. soft drink, etc. They move past Water 1.000 Clear each other. gas Particles move freely oxygen, helium, Study the table and answer the follow- with energy. They vapor move all around. ing questions. 1. A scientist has a sample of a substance19. Drawing Conclusions List the physical and with a density greater than 1 g/mL. chemical properties and changes that According to the table, which of these describe the process of scrambling eggs. substances has a density greater than 1 g/mL? A) gasoline20. Comic Strip Create a comic strip demon- B) water strating a chemical change in a substance. C) aluminum Include captions and drawings that demon- D) methane strate your understanding of conservation 2. A physical change occurs when the of matter. form or appearance of a substance is changed. All of the following are examples of physical changes TECHNOLOGY EXCEPT _____. Go to the Glencoe Science Web site at F) the vaporization of gasoline science.glencoe.com or use the G) corrosion of aluminum Glencoe Science CD-ROM for additional H) methane diluted by air chapter assessment. J) water freezing into ice CHAPTER ASSESSMENT 553