Matter and Change

Kevin Pyatt, Ph.D.Donald Calbreath, Ph.D.

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Printed: November 4, 2014

AUTHORSKevin Pyatt, Ph.D.Donald Calbreath, Ph.D.

EDITORSDonald Calbreath, Ph.D.Max Helix

www.ck12.org Chapter 1. Matter and Change

CHAPTER 1 Matter and ChangeCHAPTER OUTLINE

1.1 Properties of Matter

1.2 Classification of Matter

1.3 Changes in Matter

1.4 References

Matter is anything that has mass and takes up space. Matter is everywhere. The air we breathe, the water we drink,the food we eat, and the ground we walk on are all comprised of matter. Matter can take on a variety of differentforms which all have a variety of different properties. In this chapter, we will introduce the characteristics of matterand study how these characteristics vary in different types of matter.Image copyright A f rica Studio, 2014. www.shutterstock.com. Used under license f rom Shutterstock.com.

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1.1 Properties of Matter

Lesson Objectives

• Classify properties of materials as extensive, intensive, chemical, or physical. Give examples of each.• Describe the concepts of intensive and extensive properties and be able to describe these properties in a given

material.• Describe the concepts of physical properties and chemical properties and be able to describe these properties

for a given material.• Explain the concept of density as it relates to other physical properties of matter.

Lesson Vocabulary

• chemical properties: Properties that describe matter’s reactions with other substances.• physical properties: Properties of matter that can be observed without changing the matter’s composition.• intensive properties: Physical properties that are independent on the amount of a substance present.• extensive properties: Physical properties that depend on the amount of a substance present.

Check Your Understanding

• What are some ways that you can distinguish different substances from each other?

– For example, what is different between sand and sugar?

Introduction

All substances have special properties by which they can be identified. For instance, substances have unique colors,densities, and boiling points. They also behave in unique ways with other substances. For example, they may reactwith air, water, or acids. In chemistry, we study these properties and use them to identify and categorize matter.

Chemical Properties

All types of matter exhibit chemical properties. Chemical properties are the properties that describe matter’sreactions with other substances. We can determine these chemical properties by seeing what happens to a substancewhen it is placed in the presence of the following:

• air

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• water• an acid• a base• other chemicals

Chemical properties indicate how the composition of a substance will change when exposed to various other sub-stances. You can observe many chemical properties in the objects around you. For example, the metal frame ofa bicycle will become rusty over time. The process of the frame becoming rusty can be described by a chemicalproperty of iron, one of the metals in the frame. The iron will react with the oxygen in the air to form iron oxide, orrust.

FIGURE 1.1(A) Elemental iron. (B) Oxidized ironplate. (C) Iron “burning.”

In the Figure 1.1 we can observe the difference in color between pure iron, which is a lustrous dark gray color, andrusted iron, which is a cinnamon colored. We can also observe the reaction that takes place when iron is heated by aflame, in which the hot air to reacts more rapidly with the pure iron. The changes that iron undergoes when exposedto air show us some of iron’s chemical properties and help us to classify iron as specific type of matter.

Example 2.1

Which of the following would be examples of a chemical property?

A. Most metals will react with acids.B. Water can be a solid, liquid, or a gas.C. Water mixes well with ethanol.

Answer: A is an example of chemical properties. Statement B does not reflect chemical properties; these are physicalcharacteristics of water. The process described in answer C would not be a chemical property because no reactiontakes place. There are no changes in the composition of either the water or the ethanol as a result of the mixing, andboth components can be separated from one another using physical processes.

Physical Properties

Matter also exhibits physical properties. Physical properties are used to observe and describe matter. Physicalproperties can be observed or measured without changing the composition of matter. These are properties such asmass, weight, volume, and density. Density calculations will be discussed later on in chapter three, but for now justremember that density is a physical property.

Intensive Properties

Physical properties that do not depend on the amount of substance present are called intensive properties. Intensiveproperties do not change with changes of size, shape, or scale. Examples of intensive properties are as follows in theTable 1.1.

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TABLE 1.1:

Intensive Properties Examplecolor Aluminum metal is gray colored.taste Lemon juice (citric acid) is sour.melting point Aluminum has melting point of 660◦C.boiling point Water has a boiling point of 100◦C.density Water has a density of 1 g/mL.luster Metals are lustrous (shiny).hardness Diamond is the hardest substance known.

Extensive Properties

Physical properties that do depend on the amount of substance present are called extensive properties. Examplesof extensive properties include:

• Mass• Volume• Length

Example 2.2

Which of the following is an intensive property of a box of crackers?

A. Calories per serving.B. Total grams.C. Total number of crackers.D. Total calories.

Answer: A. Calories per serving. Total grams, total crackers, and total number of calories are extensive properties.A larger amount of crackers would have more grams, crackers, and total calories but the same number of caloriesper serving.

Example 2.3

Which of the following is an extensive property?

A. The color of charcoal is black.B. Gold is shiny.C. The volume of orange juice is 25 mL.

Answer: C. The volume of orange juice is 25 mL. Charcoal’s black color and gold’s luster are intensive properties,and are not dependent on how much charcoal or gold is present. However if you had more or less orange juice, itsvolume would not stay the same. So, this is an extensive property.

Lesson Summary

• Matter is anything that has mass and takes up space.• The properties of matter can be classified as either chemical or physical.• Chemical properties describe the reactions that can occur when matter is treated with other substances, such

as how a substance reacts with air or with an acid.

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• Physical properties, such as mass, volume, density, and color, can be observed without changing the identityof the matter.

• We can further categorize the physical properties of matter as either intensive or extensive.• Intensive properties do not depend on the amount of the substance present. Some examples of intensive

properties are color, taste, and melting point.• Extensive properties vary according to the amount of matter present. Examples of extensive properties include

mass, volume, and length.

Lesson Review Questions

1. Compare and contrast physical properties and chemical properties.2. Which of these is a chemical property?

(a) Oxygen is a gas at 25◦C.(b) Helium is very nonreactive.(c) Ice melts at 0◦C.(d) Sodium is a soft, shiny metal.

3. Indicate whether each of the following is a chemical property or a physical property. If it is a physical property,indicate whether it is an intensive or extensive property.

(a) Water boils at 100◦C.(b) Diamonds are the hardest known substance.(c) Salt is capable of dissolving in water.(d) Vinegar reacts with baking soda.(e) Most metals are lustrous.(f) Most metals react with acids.(g) A given sample of lead weighs 4.5 g.(h) The length of a piece of aluminum foil is 12.2 cm.(i) Gold conducts electricity.

Further Reading / Supplemental Links

• Examples of laboratory techniques used for separating mixtures: http://sciencepark.etacude.com/projects/

Points to Consider

• How could you categorize types of matter based on differing chemical and physical properties?

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1.2 Classification of Matter

Lesson Objectives

• Distinguish between gases, liquids, and solids. Explain how these states differ at the molecular level.• Classify samples of matter as pure substances, homogeneous mixtures, heterogeneous mixtures, compounds,

and elements.• Use sketches to show how elements, compounds, and mixtures differ at the molecular level.• Describe six different techniques for separating mixtures.• Relate the names of elements to their international element symbols.• Name the major groups and regions on the periodic table and identify elements belonging to these groups.• Distinguish between metals, nonmetals, and metalloids using the periodic table.

Lesson Vocabulary

• pure substances: Have a constant composition and can only be changed by chemical reactions.• elements: Substances that cannot be decomposed into simpler substances by chemical or physical means.• compounds: Substances that can be broken down into their individual elements, but only through chemical

processes.• mixtures: A combination of two or more pure substances.• homogeneous mixtures: A mixture with uniform composition throughout.• heterogeneous mixtures: A mixture with visibly distinguishable components, exist primarily in the solid and

liquid states.

Check Your Understanding

• Give some examples of chemical properties and physical properties of matter.• What would be some chemical and physical properties of the following substances:

– a glass of water– aluminum foil– argon

Introduction

As we studied in our last lesson, matter can be described by its physical and chemical properties. We have seenexamples of how matter exhibits specific physical and chemical properties, which can be used to distinguish onetype of matter from another. In this lesson, we are going to use these properties to categorize the various forms ofmatter.

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States of Matter

Matter typically exists in one of three states: solid, liquid, or gas. The state of a given substance is a physicalproperty. Some substances exist as gases at room temperature (such as oxygen and carbon dioxide), while others(like water and mercury metal) exist as liquids. Most metals exist as solids at room temperature. All substances canexist in any of these three states.

Water is a very common substance that we frequently encounter in all three states of matter, as seen in Figure 1.2.When water is in the solid state, we call it ice, while water in the gaseous state is referred to as steam or water vapor.The physical state of matter is a physical property because the identity of a pure substance does not change when itis melted, frozen, or boiled.

FIGURE 1.2Water is the same substance in any ofits three states. (A) A frozen waterfall inHungary. (B) The Nile River in Egypt. (C)A steam powered train in Wales.

Solid

A solid is a form of matter that has a definite shape and volume. The shape of a solid does not change if it istransferred from one container to another. The particles of a solid are packed tightly together in fixed positions,usually in an orderly arrangement. Solids are almost completely incompressible, meaning that solids cannot besqueezed into a smaller volume. When a solid is heated or cooled, it expands or contracts only slightly.

Liquid

A liquid is a form of matter that has a definite volume, but an indefinite shape. As water is poured from one containerinto another, it adopts the shape of its new container. However, the volume of the water does not change, becausethe water molecules are still relatively close to one another in the liquid state. Unlike a solid, the arrangement ofparticles in a liquid is not rigid and orderly. Liquids are also incompressible.

Gas

A gas is a form of matter that has neither a definite shape nor a definite volume. A gas takes up the shape and volumeof its container. This is because the particles of a gas are very far apart from one another compared to the particlesthat make up solids and liquids. Gases are easily compressed because of the large spaces in between gas particles.Gas particles are often invisible, but they can be detected in various ways, such as the light emitted when an electriccurrent is passed through a sample of a gas ( Figure 1.3).

Molecular View of Solids, Liquids, and Gases

We are quite familiar with the properties of solids, liquids, and gases from our everyday experience. These propertiesare fundamentally based on differences in the arrangement of atoms or molecules at the microscopic level. Figure

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FIGURE 1.3Sodium vapor lamps glow with a distinc-tive yellow color.

1.4 shows the differences between the ways in which particles appear in each of these three states. Remember, anysubstance can be present as a gas, liquid, or solid when placed under specific conditions.

FIGURE 1.4The particles of a gas are very far apartcompared to the particles of a liquid or asolid.

As Figure 1.4 shows, the distance between particles is much smaller for the solid and liquid states than for the gasstate. In the solid state, particles are fixed in place, while particles are more free to move in the liquid and gas states.The particles in the solid and liquid states “stick together,” but in the gas state, they move freely about the container.In general, it requires energy to separate individual particles. If we want to make a solid adopt a liquid form, wecan add energy in the form of heat, increasing the temperature of the substance. Conversely, if we want to converta substance from a gas to a liquid or from a liquid to a solid, we remove energy from the system and decrease thetemperature. Pressure also plays an important role in changes of state, which will be discussed later on. We willstudy these difference in greater detail in the chapter States of Matter.

Pure Substances

When studying the different states that matter exhibits, we have been looking at pure substances. Pure substanceshave a constant composition and can only be changed through chemical reactions. Constant composition indicatesthat a sample of a pure substance always contains the same elements in the same proportions. There are two maintypes of pure substances:

• elements: Substances that cannot be decomposed into simpler substances by chemical or physical means.• compounds: Substances that can be broken down into elements through chemical means.

Figure 1.5 shows pure substances in the form of elements and compounds.

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FIGURE 1.5Pure substances: (left) the element sulfurand (right) the compound water.

The image on the left shows elemental sulfur in the solid state. The image on the right shows water in its liquid form.Sulfur is a pure element, and water is a compound comprised of the elements hydrogen and oxygen. Both of thesesubstances have a constant composition, but water can be broken down into its elements, whereas sulfur cannot bedecomposed into a simpler substance. Water can be broken down into its elements by passing electricity through asalt solution.

Periodic Table of Elements

Chemists have classified and organized all of the known elements into what is called the periodic table. All knownsubstances are made of some combination of these elements. The periodic table is a tool that we use to help identifyand describe the composition of a given substance. All pure substances which cannot be broken down further, whichwe have called elements, are displayed in the periodic table. Figure 1.6 shows our modern periodic table. We willstudy the periodic table in more detail in the chapter The Periodic Table.

Mixtures

When two or more pure substances are combined together, a mixture is formed. Unlike pure substances, mixtureshave a variable composition. Variable composition indicates that the relative proportions of the mixtures componentsmay vary, and they can be separated by physical methods. There are two main types of mixtures.

Homogeneous Mixtures

A homogeneous mixture is one in which the composition is uniform throughout the mixture. A glass of salt wateris a homogeneous mixture because the dissolved salt is evenly distributed throughout the entire sample. It is ofteneasy to confuse a homogeneous mixture with a pure substance because they are both uniform, and it can be difficultto tell which type you have by the naked eye. The difference is that the composition of the pure substance is alwaysthe same, while the composition of a homogeneous mixture can vary. For example, you may dissolve a small amountor a large amount of salt into a given sample of water. Although the ratio of salt to water will differ, the mixtureswill both be homogeneous. However, pure water will always have the same ratio of elements that make it a puresubstance (two hydrogen atoms per oxygen atom).

Wine, air, and gunpowder are other examples of common homogeneous mixtures ( Figure 1.7). Their exactcompositions can vary, making them mixtures rather than pure substances. Wine is a liquid mixture of water,

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FIGURE 1.6The modern periodic table.

ethanol, and a variety of other dissolved substances. Air is a mixture of nitrogen gas (78%), oxygen gas (21%), andsmall amounts of various other gases. Gunpowder is a solid mixture comprised of potassium nitrate (75%), charcoal(15%) and sulfur (10%).

FIGURE 1.7Examples of homogenous mixtures: wineand gunpowder.

In the Figure 1.7, we see that the components of these mixtures cannot be distinguished from one another. However,the substances comprising these mixtures can be separated through physical means.

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Heterogeneous Mixtures

Heterogeneous mixtures have visibly distinguishable parts. These mixtures will typically exist in the solid or liquidstates, but not the gas state. Gas state heterogeneous mixtures are not possible because gas particles freely mix anddisperse. Heterogeneous mixtures are quite common. For example, oil-and-vinegar salad dressing is a heterogeneousmixture that is in the liquid state. Its composition varies and typically includes olive oil mixed with red vinegar. Anexample of a solid heterogeneous mixture is soil. Soil is primarily comprised of organic and inorganic material,including substances like decaying plants and animals, minerals, water, and air. The composition of soil variesgreatly from one location to another. Figure 1.8 shows these mixtures.

FIGURE 1.8Examples of heterogeneous mixtures:(left) oil and vinegar and (right) soil.

The substances that comprise heterogeneous mixtures can also be separated by physical means. We will discussseparation techniques in the following lesson.

Lesson Summary

• Matter exhibits specific physical and chemical properties.• Matter can exist in one of three states: solid, liquid, or gas.• In the solid state, particles are fixed in place relative to one another. In the liquid and gas states, individual

particles are free to move.• Under the right pressure conditions, lowering the temperature of a substance in the gas state causes the

substance to liquefy. The opposite effect occurs if temperature is increased.• Under the right pressure conditions, lowering the temperature of a substance in the liquid state causes the

substance to solidify. The opposite effect occurs if the temperature is increased.• Pure substances have a constant composition and can only be changed by chemical reactions. They can be

classified as either elements or compounds.• Elements are substances that cannot be decomposed into simpler substances by chemical or physical means.

Compounds, however, can be broken down further through chemical, but not physical, means.• The periodic table is a tool that we use to help identify and describe the composition of a given substance. The

table is an arrangement of elements based on their physical and chemical properties.• Homogeneous or heterogeneous mixtures are formed when two or more pure substances are combined. A

homogeneous mixture has a uniform distribution throughout the sample, whereas a heterogeneous mixturehas visibly distinguishable components.

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Lesson Review Questions

1. Compare and contrast the three states of matter. Try to describe similarities and differences apparent at amicroscopic level as well as at the observable level between these states of matter.

2. Which of the following would be an example of a pure substance?

a. plasticb. milkc. 100% ethanold. cake flour

3. Which of the following would be an example of an element?

a. waterb. orange juicec. steeld. iron

4. Which of the following would be an example of a compound?

a. waterb. sulfurc. aluminumd. brass

5. Compare and contrast a pure substance with a mixture and give an example.6. Which of the following statements is true?

a. The periodic table is a list of various compounds found throughout the world.b. The periodic table is randomly organized.c. The periodic table has been the same for 50 years.d. The periodic table is an organized assembly of the various elements that have been discovered.

7. Classify the following as a homogeneous mixture, a heterogeneous mixture, or neither.

a. powdered sugarb. mayonnaisec. scrambled eggd. aire. soda popf. concreteg. apple juiceh. glassi. steelj. copper

Further Reading / Supplemental Links

• Examples of laboratory techniques used for separating mixtures can be found at Science Park: http://sciencepark.etacude.com/projects/

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Points to Consider

• As we saw, compounds can be broken down into their elemental components. How might you go aboutbreaking down a compound into its elements?

• The components that comprise homogeneous and heterogeneous mixtures can be separated out by physicalmeans. How might you go about separating out components of a soil mixture?

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1.3 Changes in Matter

Lesson Objectives

• Describe methods for separating mixtures, such as chromatography, distillation, fractional distillation, evapo-ration, and filtration.

• Given a specific mixture, propose methods by which the mixture’s components could be isolated.• Identify the chemical properties of a substance.• Describe chemical changes and differentiate them from physical changes.• Use various visual clues to identify whether a chemical reaction is taking place.

Lesson Vocabulary

• chemical change: A change during which the chemical identity of a substance is altered. Chemical changesare often accompanied by a change in color, temperature, or odor, or the production of a gas or precipitate.

• physical change: A change in which the physical form and properties of a substance change.• chromatography: The separation of a mixture by passing it through a medium in which the components move

at different rates.• distillation: A purification process in which the components of a liquid mixture are vaporized and then

condensed and isolated.• evaporation: A technique used to separate out homogeneous mixtures in which one or more solids are

dissolved in a liquid.• filtration: A method used to separate mixtures in which some of the particles are large enough in size to be

captured with a porous material while others are not.• chemical property: The ability of a substance to undergo a specific chemical change.

Check Your Understanding

• Compare and contrast chemical properties and physical properties.• Give examples of physical properties and chemical properties.• Compare and contrast the following pairs of terms: element and compound; pure substance and mixture.

Introduction

In the previous lesson, we discussed pure substances and mixtures. We indicated that the components of a mixturecould be separated by physical means, but the components of a pure substance could not. Pure substances can onlybe broken down further through chemical means. In this lesson, we list several methods for separating mixtures. Wewill also be looking at chemical changes which alter the chemical identity of a substance, and how to recognizewhen a chemical change is taking place.

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Physical Change

Any time the physical properties of a substance are changed, we can say the substance has undergone a physicalchange. All substances undergo physical changes where there is a change in the form of the substance but not inits chemical composition. For instance, the grinding of granular sugar into powdered sugar is a physical change.Similarly, dissolving sugar in water is a physical change. We can also use physical changes to separate mixtures intotheir components. There are a variety of methods used, and the best procedure depends largely on the nature of themixture. Depending on the states of matter involved, the relative sizes of the mixtures components, and whether themixture is homogeneous or heterogeneous will determine the necessary separation technique.

Methods for Separating Mixtures

Chromatography

Chromatography is the separation of a mixture by passing it through a medium in which the components moveat different rates. Mixtures that are solutions (such as salt water), suspensions (such as sand mixed with water),or even vapors can be separated in this way. Paper chromatography is a type of chromatography that can be usedfor separating and identifying mixtures in which one or more components are colored, especially pigments. Thefollowing video shows paper chromatography being used to separate out the dyes present in a variety of water-soluble inks: http://www.youtube.com/watch?v=ac9vALSoxbY (0:43).

MEDIAClick image to the left for use the URL below.URL: http://www.ck12.org/flx/render/embeddedobject/65294

In this video, we see several different dyes that have been placed on paper through which water was absorbed.Dyes, such as the ink in colored markers, are usually a mixture of several different colored compounds. The dyes inwater-soluble inks dissolve easily in water, while permanent inks dissolve more readily in organic solvents such asethanol.

Distillation

Distillation is an effective method to separate mixtures comprised of two or more pure liquids. Distillation is apurification process in which the components of a liquid mixture are vaporized (transformed from liquid to gas) andthen condensed (transformed from gas back to liquid) and isolated. In a simple distillation, a mixture is graduallyheated. The solution with the lowest boiling point will change into a gas first. This gas, or vapor, then passes througha cooled tube (a condenser) where it condenses back into its liquid state. This condensed liquid is called the distillate.Figure 1.9 illustrates this.

When a mixture contains several components with similar boiling points, the one-step distillation may not givea pure substance in the receiving vessel. Therefore, more elaborate methods are used to completely separate amixtures components. Distillation is an especially effective physical technique in separating out a homogeneousmixture comprised of two or more pure liquids, such as alcohol and water.

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FIGURE 1.9In this figure, we see several importantpieces of equipment. There is a heatsource and a flask containing the liquid tobe distilled. At the center of the set-up isthe condenser. The distillate is collectedin a flask. There are other more compli-cated assemblies for distillation that canalso be used, especially to separate mix-tures which are comprised of pure liquidswith boiling points that are close to oneanother.

Evaporation

Evaporation is a technique used to separate out homogeneous mixtures in which one or more solids are dissolvedin a liquid. Typically, the mixture is heated until all of the liquid has vaporized, leaving behind the dissolved solids( Figure 1.10). The vapor can also be captured and recondensed into a liquid if desired.

FIGURE 1.10Evaporation

This method can only be used to separate volatile liquid components (those which will evaporate at low temperatures)from nonvolatile solid components (those which will not evaporate at low temperatures). If there is more than oneliquid or solid component, that portion of the mixture cannot be isolated purely.

Filtration

Filtration can be used to separate mixtures in which the some of the particles are large enough in size to be capturedwith a porous material while others are not. Particle sizes can vary considerably. For instance, stream water is a

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mixture that contains naturally occurring biological organisms like bacteria, viruses, and protozoans. Some waterfilters can filter out bacteria, the length of which is on the order of 1 micrometer. Other mixtures, like wet soil,contain relatively large particles that can be filtered out using something like a coffee filter.

Chemical Change

Much of the field of chemistry is devoted to the study of chemical changes. A chemical change, also referred to asa chemical reaction, is one in which the chemical identity of a substance is altered. We witness chemical changesevery day. For example, the burning of wood or the rusting of iron are chemical changes. The burning of wood is aprocess in which cellulose molecules break down into water and carbon dioxide. The rusting of iron is a process inwhich elemental iron combines with oxygen (from air or water) to produce iron oxide ( Figure 1.11).

FIGURE 1.11Rust (iron oxide) forms on an unprotectediron surface.

As the rust forms on the surface of the iron, it flakes off to expose more iron, which will continue to rust. Rustis clearly a substance that is different from iron. Rusting is an example of a chemical change. Some chemicalchanges are not as obvious but are still hugely important. For example, photosynthesis and cellular respiration arechemical changes that we could not live without. Chemical changes involve the combination, decomposition, orrearrangement of elements and compounds to form new substances.

A chemical property describes the ability of a substance to undergo a specific chemical change. A chemicalproperty of iron is that it is capable of combining with oxygen to form iron oxide, the chemical name of rust. A moregeneral term for rusting and other similar processes is corrosion. Other terms that are commonly used in descriptionsof chemical changes are burn, rot, explode, decompose, and ferment. Chemical properties are very useful as a wayof identifying substances. However, unlike physical properties, chemical properties can only be observed as thesubstance is in the process of being changed into a different substance.

Recognizing Chemical Changes

How can you tell if a chemical change is taking place? Certain visual clues indicate that a chemical change is likely(but not necessarily) occurring, including the following examples:

1. A change of color occurs.

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2. A gas is produced.3. A solid product called a precipitate is produced.4. A change of energy is apparent, due to a change in temperature or the appearance of light such as a flame.

Mercury(II) oxide is a red solid. When it is heated to a temperature above 500°C, it easily decomposes into mercuryand oxygen gas. The red color of the reactant, mercury oxide, is gradually replaced by the silver color of the product,mercury. The color change is one sign that this reaction is occurring. Watch this decomposition take place at http://www.youtube.com/watch?v=_Y1alDuXm6A (1:12).

MEDIAClick image to the left for use the URL below.URL: http://www.ck12.org/flx/render/embeddedobject/59229

When zinc reacts with hydrochloric acid, the reaction bubbles vigorously as hydrogen gas is produced ( Figure1.12). The production of a gas is also an indication that a chemical reaction may be occurring.

FIGURE 1.12Zinc reacts with hydrochloric acid to pro-duce bubbles of hydrogen gas.

When a colorless solution of lead(II) nitrate is added to a colorless solution of potassium iodide, a yellow solidcalled a precipitate is instantly produced ( Figure 1.13). A precipitate is a solid product that forms from a reactionand settles out of a liquid mixture. The formation of a precipitate may also indicate the occurrence of a chemicalreaction.

All chemical changes involve a transfer of energy. When zinc reacts with hydrochloric acid, the test tube becomesvery warm as energy is released during the reaction. Some other reactions absorb energy. While energy changes area potential sign of a chemical reaction, care must be taken to ensure that a chemical reaction is indeed taking place.Physical changes may also involve a transfer of energy. A solid absorbs energy when it melts, and the condensation

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FIGURE 1.13A yellow precipitate of solid lead(II) io-dide forms immediately when solutions oflead(II) nitrate and potassium iodide aremixed.

of a gas releases energy. The only way to be certain that a chemical reaction has occurred is to test the compositionof the substances after the change has taken place to see if they are different from the starting substances.

Lesson Summary

• Matter can undergo chemical and physical changes.• Mixtures can be separated through physical changes, including techniques such as chromatography, distilla-

tion, evaporation, and filtration. Physical changes do not alter the nature of the substance, they simply alterthe form.

• Pure substances, such as compounds, can be separated through chemical changes. Chemical changes changethe chemical composition of a substance and can only occur through a chemical reaction.

• Four clues to a possible chemical reaction include a color change, the production of a gas, the formation of aprecipitate, and an observable transfer of energy.

Lesson Review Questions

1. Can elements be broken down further into other pure substances?2. For each of the following mixtures, describe how you might separate out the components using one of the

techniques discussed in this chapter.

a. separating dyes in inksb. separating sand from waterc. separating ethanol from waterd. separating water from inke. separating salt from water

3. A candle is a mixture of substances that, when burned, breaks down primarily into carbon dioxide and water.How might you test for the presence of water that is produced when a candle is burned?

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4. Carbonated beverages contain carbon dioxide gas that is dissolved in solution. Do you think a carbonatedbeverage is a mixture or a pure substance? Explain.

5. Classify each of the following as a chemical change or a physical change.

a. Sugar dissolves in water.b. A peach rots.c. Icicles melt in the warm sunlight.d. A baking cake rises in the oven.e. A leaf changes its color in the fall.f. Food coloring is added to a glass of water.

6. The Figure 1.14 shows two different mixtures. The mixture on the left is comprised of muddy water, whilethe mixture on the right is a mixture of sugar and water. Describe how you might go about separating out thecomponents of each of these mixtures.

FIGURE 1.14(left) Muddy water. (right) Sugar water.

Further Reading / Supplemental Links

• School Science Lessons: http://www.uq.edu.au/_School_Science_Lessons/topic10.html• Examples of laboratory techniques used for separating mixtures at Science Park: http://sciencepark.etacude.c

om/projects/• Ophardt, Charles E. 2011. Virtual Chembook. Elmhurst College 20032011. Available from: http://www.e

lmhurst.edu/~chm/vchembook/index.html

Points to Consider

• We have thus far assumed that elements cannot be broken down further into constituent parts. Is this com-pletely true?

• What do you suppose elements are comprised of and how might you be able to distinguish or measure thecomponents of an element?

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www.ck12.org Chapter 1. Matter and Change

1.4 References

1. (A) Hi-Res Images of Chemical Elements; (B) Jordan McCullough; (C) Jo Naylor. (A) http://images-of-elements.com/iron.php; (B) http://www.flickr.com/photos/ambientideas/3297063530/; (C) http://www.flickr.com/photos/pandora_6666/3454172058/ . (A) CC BY 3.0; (B) CC BY 2.0; (C) CC BY 2.0

2. (A) Rodrigo; (B) Christine und David Schmitt (Flickr:cheesy42); (C) Steven Whateley. (A) http://commons.wikimedia.org/wiki/File:Lillafured_icedwaterfall_wman.jpg; (B) http://commons.wikimedia.org/wiki/File:Nile_river_at_Luxor_2007.jpg; (C) http://commons.wikimedia.org/wiki/File:Steam_Train.JPG . (A) CC BY2.5; (B) CC BY 2.0; (C) Public Domain

3. User:Proton02/Wikimedia Commons. http://commons.wikimedia.org/wiki/File:LPS_Lamp_35W_running.jpg. Public Domain

4. Christopher Auyeung. CK-12 Foundation . CC BY-NC 3.05. Sulfur: Hi-Res Images of Chemical Elements; Water: Claire Cessford. Sulfur: http://commons.wikimedia

.org/wiki/File:Sulfur_%2816_S%29.jpg; Water: http://www.flickr.com/photos/35137234@N06/4230612281/. Sulfur: CC BY 3.0; Water: CC BY 2.0

6. User:Cepheus/Wikimedia Commons. http://commons.wikimedia.org/wiki/File:Periodic_table.svg . PublicDomain

7. Wine: George Hodan; Gunpowder: Oliver H.. Wine: http://www.publicdomainpictures.net/view-image.php?image=35183&picture=glass-of-red-wine; Gunpowder: http://commons.wikimedia.org/wiki/File:Spk-RZ.jpg. Public Domain

8. Oil/vinegar: Kat (Flickr:tyger_lyllie); Soil: Petr Kratochvil. Oil/vinegar: http://www.flickr.com/photos/tyger_lyllie/3350276971/; Soil: http://www.publicdomainpictures.net/view-image.php?image=13200&picture=soil-texture . Oil/vinegar: CC BY 2.0; Soil: Public Domain

9. Pearson Scott Foresman. http://commons.wikimedia.org/wiki/File:Distillation_%28PSF%29.png . PublicDomain

10. Laura Guerin. CK-12 Foundation . CC BY-NC 3.011. Duff Axsom (Flickr:duff_sf). http://www.flickr.com/photos/sfbear/472100458/ . CC BY 2.012. User:Chemicalinterest/Wikimedia Commons. http://commons.wikimedia.org/wiki/File:Zn_reaction_with_-

HCl.JPG . Public Domain13. Paige Powers (Flickr:paigggeyy). http://www.flickr.com/photos/paigggeyy/5533819494/ . CC BY 2.014. Muddy water: Image copyright Alena Brozova, 2014; Sugar water: Image copyright m.bonotto, 2014. http

://www.shutterstock.com . Used under licenses from Shutterstock.com

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