A Groovy Kind of MixtureWhen you look at these lamps, you can easily see two dif-ferent liquids inside them. This mixture is composed ofmineral oil, wax, water, and alcohol. The water and alcohol mix, but they remain separated from the globs ofwax and oil. In this chapter, you will learn not only aboutmixtures but also about the elements and compounds that can form mixtures.
◆ Describe pure substances.◆ Describe the characteristics of
elements, and give examples.◆ Explain how elements can be
identified.◆ Classify elements according to
their properties.
Chapter 482
ElementsImagine you are working as a lab technician for the Break-It-Down Corporation. Your job is to break down materialsinto the simplest substances you can obtain. One day a ma-terial seems particularly difficult to break down. You crushand grind it. You notice that the resulting pieces are smaller,but they are still the same material. You try other physicalchanges, including melting, boiling, and filtering it, but thematerial does not change into anything simpler.
Next you try some chemical changes. You pass an elec-tric current through the material but it still does not becomeany simpler. After recording your observations, you analyzethe results of your tests. You then draw a conclusion: thesubstance must be an element. An element is a pure sub-stance that cannot be separated into simpler substances byphysical or chemical means, as shown in Figure 1.
An Element Has Only One Type of ParticleA pure substance is a substance in which there is only onetype of particle. Because elements are pure substances, eachelement contains only one type of particle. For example, everyparticle (atom) in a 5 g nugget of the element gold is likeevery other particle of gold. The particles of a pure substanceare alike no matter where that substance is found, as shownin Figure 2. Although a meteorite might travel more than 400 million kilometers (about 248 million miles) to reach Earth,the particles of iron in a meteorite are identical to the parti-cles of iron in objects around your home!
Figure 1 No matterwhat kind of physical orchemical change youattempt, an elementcannot be changed intoa simpler substance!
Figure 2 The atoms of theelement iron are alike whetherthey are in a meteorite or in acommon iron skillet.
Every Element Has a Unique Set of PropertiesEach element has a unique set of properties that allows youto identify it. For example, each element has its own charac-teristic properties. These properties do not depend on the amountof material present in a sample of the element. Characteristicproperties include some physical properties, such as boilingpoint, melting point, and density, as well as chemical prop-erties, such as reactivity with acid. The elements helium andkrypton are unreactive gases. However, the density (mass perunit volume) of helium is less than the density of air. Therefore,a helium-filled balloon will float up if it is released. Kryptonis more dense than air, so a krypton-filled balloon will sink tothe ground if it is released.
Identifying Elements by TheirProperties Look at the elementscobalt, iron, and nickel, shown inFigure 3. Even though these threeelements have some similar prop-erties, each can be identified byits unique set of properties.
Notice that the physical prop-erties for the elements in Figure 3include melting point and den-sity. Other physical properties,such as color, hardness, and tex-ture, could be added to the list.Also, depending on the elementsbeing identified, other chemicalproperties might be useful. Forexample, some elements, such ashydrogen and carbon, are flam-mable. Other elements, such assodium, react immediately withoxygen. Still other elements, suchas zinc, are reactive with acid.
Elements, Compounds, and Mixtures 83
Figure 3 Like all other elements,cobalt, iron, and nickel can be identified by their unique combinationof properties.
Melting point is 1,495°C.Density is 8.9 g/cm3.Conducts electric current andthermal energy.Unreactive with oxygen in the air.
Cobalt
Melting point is 1,535°C.Density is 7.9 g/cm3.Conducts electric current andthermal energy.Combines slowly with oxygenin the air to form rust.
Iron
Melting point is 1,455°C.Density is 8.9 g/cm3.Conducts electric current andthermal energy.Unreactive with oxygen in the air.
Elements Are Classified by Their PropertiesConsider how many different breeds of dogs thereare. Consider also how you tell one breed fromanother. Most often you can tell just by their appear-
ance, or what might be called physical proper-ties. Figure 4 shows several breeds of dogs,
which all happen to be terriers. Many ter-riers are fairly small in size and have shorthair. Although not all terriers are exactlyalike, they share enough common prop-erties to be classified in the same group.
Elements Are Grouped into CategoriesElements are classified into groups accord-ing to their shared properties. Recall theelements iron, nickel, and cobalt. All threeare shiny, and all three conduct thermalenergy and electric current. Using theseshared properties, scientists have groupedthese three elements, along with othersimilar elements, into one large groupcalled metals. Metals are not all exactlyalike, but they do have some propertiesin common.
If You Know the Category, You Know the Properties Ifyou have ever browsed at a music store, you know that the CDsare categorized by type of music. If you like rock-and-roll, youwould go to the rock-and-roll section. You might not recognizea particular CD, but you know that it must have the character-istics of rock-and-roll for it to be in this section.
Likewise, you can predict some of theproperties of an unfamiliar element byknowing the category to which it belongs.As shown in the concept map in Figure 5,elements are classified into three cat-egories—metals, nonmetals, and metal-loids. Cobalt, iron, and nickel are classifiedas metals. If you know that a particularelement is a metal, you know that it sharescertain properties with iron, nickel, andcobalt. The chart on the next page showsexamples of each category and describesthe properties that identify elements ineach category.
Chapter 484
Figure 4 Even though these dogs are differentbreeds, they have enough in common to be classifiedas terriers.
Metals Nonmetals Metalloids
are divided into
Elements
Figure 5 Elements are divided into three categories:metals, nonmetals, and metalloids.
2. List three properties that can be used to classify elements.
3. Applying Concepts Which category of element would be the least appropriate choice for making a containerthat can be dropped without shattering? Explain yourreasoning.
REVIEW
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TOPIC: ElementsGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP085
MetalloidsMetalloids, also called semiconductors, are elementsthat have properties of both metals and nonmetals.Some metalloids are shiny, while others are dull.Metalloids are somewhat malleable and ductile. Somemetalloids conduct thermal energy and electric currentwell. Silicon is used to make computer chips. However,other elements must be added to silicon to make aworking chip.
MetalsMetals are elements that are shiny and aregood conductors of thermal energy and elec-tric current. They are malleable (they can behammered into thin sheets) and ductile (theycan be drawn into thin wires). Iron has manyuses in building and automobile construction.Copper is used in wires and coins.
The Three Major Categories of Elements
Sulfur
NonmetalsNonmetals are elements that are dull (not shiny) andthat are poor conductors of thermal energy and elec-tric current. Solid nonmetals tend to be brittle andunmalleable. Few familiar objects are made of onlynonmetals. The neon used in lights is a nonmetal, asis the graphite (carbon) used in pencils.
◆ Identify the differences betweenan element and a compound.
◆ Give examples of common compounds.
Chapter 486
CompoundsMost elements take part in chemical changes fairly easily, sofew elements are found alone in nature. Instead, most elementsare found combined with other elements as compounds.
A compound is a pure substance composed of two or moreelements that are chemically combined. In a compound, a par-ticle is formed when atoms of two or more elements jointogether. In order for elements to combine, they must react, orundergo a chemical change, with one another. In Figure 6, yousee magnesium reacting with oxygen to form a compound calledmagnesium oxide. The compound is a new pure substance thatis different from the elements that reacted to form it. Mostsubstances you encounter every day are compounds. The tableat left lists some familiar examples.
Elements Combine in a Definite Ratio to Form a CompoundCompounds are not random combinations of elements. Whena compound forms, the elements join in a specific ratio accord-ing to their masses. For example, the ratio of the mass of hydro-gen to the mass of oxygen in water is always the same—1 gof hydrogen to 8 g of oxygen. This mass ratio can be writtenas 1:8 or as the fraction 1/8. Every sample of water has this1:8 mass ratio of hydrogen to oxygen. If a sample of a com-pound has a different mass ratio of hydrogen to oxygen, thecompound cannot be water.
� table salt—sodium and chlorine
� water—hydrogen and oxygen
� sugar—carbon, hydrogen, and oxygen
� carbon dioxide—carbon and oxygen
� baking soda—sodium, hydrogen, carbon, and oxygen
Familiar Compounds Figure 6 As magnesium burns, it reacts with oxygenand forms the compound magnesium oxide.
Every Compound Has a Unique Set of PropertiesEach compound has a unique set of properties that allows youto distinguish it from other compounds. Like elements, eachcompound has its own physical properties, such as boilingpoint, melting point, density, and color. Compounds can alsobe identified by their different chemical properties. Some com-pounds, such as the calcium carbonate found in chalk, reactwith acid. Others, such as hydrogen peroxide, react whenexposed to light. You can see how chemical properties can beused to identify compounds in the QuickLab at right.
A compound has different properties from the elementsthat form it. Did you know that ordinary table salt is a com-pound made from two very dangerous elements? Table salt—sodium chloride—consists of sodium (which reacts violentlywith water) and chlorine (which is poisonous). Together, how-ever, these elements form a harmless compound with uniqueproperties. Take a look at Figure 7. Because a compound hasdifferent properties from the elements that react to form it,sodium chloride is safe to eat and dissolves (without explod-ing!) in water.
Elements, Compounds, and Mixtures 87
Self-CheckDo the properties of pure water from a glacier andfrom a desert oasis differ? (See page 724 to checkyour answer.)
Figure 7 Table salt is formed when theelements sodium and chlorine join. Theproperties of salt are different from theproperties of sodium and chlorine.
Chlorine is a poisonous,greenish yellow gas.
Sodium is a soft, silverywhite metal that reactsviolently with water.
Sodium chloride, or table salt, isa white solid that dissolves easilyin water and is safe to eat.
Compound Confusion
1. Measure 4 g (1 tsp)of compound A,and place it in aclear plastic cup.
2. Measure 4 g (1 tsp)of compound B,and place it in asecond clear plastic cup.
3. Observe the color andtexture of each compound.Record your observations.
4. Add 5 mL (1 tsp) ofvinegar to each cup.Record your observations.
5. Baking soda reacts withvinegar, while powderedsugar does not. Which ofthese compounds iscompound A, and which iscompound B?
Compounds Can Be Broken Down intoSimpler SubstancesSome compounds can be broken down into elements throughchemical changes. Look at Figure 8. When the compound mer-cury(II) oxide is heated, it breaks down into the elements mer-cury and oxygen. Likewise, if an electric current is passedthrough melted table salt, the elements sodium and chlorineare produced.
Other compounds undergo chemical changes to form sim-pler compounds. These compounds can be broken down intoelements through additional chemical changes. For example,carbonic acid is a compound that helps to give carbonated bev-erages their “fizz,” as shown in Figure 9. The carbon dioxideand water that are formed can be further broken down intothe elements carbon, oxygen, and hydrogen through additionalchemical changes.
Compounds Cannot Be Broken Down by Physical ChangesThe only way to break down a compound is through a chemi-cal change. If you pour water through a filter, the water willpass through the filter unchanged. Filtration is a physicalchange, so it cannot be used to break down a compound.Likewise, a compound cannot be broken down by being groundinto a powder or by any other physical process.
Chapter 488
The process of using electric currentto break compounds into simplercompounds and elements is knownas electrolysis. Electrolysis can beused to separate water into hydro-gen and oxygen. The elementsaluminum and copper and thecompound hydrogen peroxide are important industrial productsobtained through electrolysis.
PhysicsC O N N E C T I O N
Figure 8 Heating mercury(II)oxide causes a chemical changethat separates it into the el-ements mercury and oxygen.
Oxygen
Mercury
Mercury(II) oxide
Figure 9 Opening a carbonated drink can be messy as carbonicacid breaks down into two simplercompounds—carbon dioxide and water.
Compounds in Your WorldYou are always surrounded by compounds.Compounds make up the food you eat, theschool supplies you use, the clothes youwear—even you!
Compounds in Nature Proteins are com-pounds found in all living things. The el-ement nitrogen is needed to make proteins.Figure 10 shows how some plants get thenitrogen they need. Other plants use nitro-gen compounds that are in the soil. Animalsget the nitrogen they need by eating plantsor by eating animals that have eaten plants.As an animal digests food, the proteins inthe food are broken down into smaller com-pounds that the animal’s cells can use.
Another compound that plays an impor-tant role in life is carbon dioxide. You exhalecarbon dioxide that was made in your body.Plants take in carbon dioxide and use it tomake other compounds, including sugar.
Compounds in Industry The element nitrogen is combinedwith the element hydrogen to form a compound called ammo-nia. Ammonia is manufactured for use in fertilizers. Plants canuse ammonia as a source of nitrogen for their proteins. Othermanufactured compounds are used in medicines, food preser-vatives, and synthetic fabrics.
The compounds found in nature are usually not the rawmaterials needed by industry. Often, these compounds mustbe broken down to provide elements used as raw material. Forexample, the element aluminum, used in cans, airplanes, andbuilding materials, is not found alone in nature. It is producedby breaking down the compound aluminum oxide.
Elements, Compounds, and Mixtures 89
1. What is a compound?
2. What type of change is needed to break down a compound?
3. Analyzing Ideas A jar contains samples of the elementscarbon and oxygen. Does the jar contain a compound?Explain.
REVIEW
Figure 10 The bumps on theroots of this pea plant are hometo bacteria that form compoundsfrom atmospheric nitrogen. Thepea plant makes proteins fromthese compounds.
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◆ Describe methods of separatingthe components of a mixture.
◆ Analyze a solution in terms of its solute, solvent, and concentration.
◆ Compare the properties of solu-tions, suspensions, and colloids.
Chapter 490
MixturesHave you ever madeyour own pizza? Youroll out the dough, adda layer of tomato sauce,then add toppings likegreen peppers, mushrooms,and olives—maybe even somepepperoni! Sprinkle cheese ontop, and you’re ready to bake. Youhave just created not only a pizza butalso a mixture—and a delicious one at that!
Properties of MixturesAll mixtures—even pizza—share certain properties. A mixtureis a combination of two or more substances that are not chemi-cally combined. Two or more materials together form a mix-ture if they do not react to form a compound. For example,cheese and tomato sauce do not react when they are used tomake a pizza.
Substances in a Mixture Retain TheirIdentity Because no chemical changeoccurs, each substance in a mixturehas the same chemical makeup it had
before the mixture formed. That is, eachsubstance in a mixture keeps its iden-tity. In some mixtures, such as the pizzaabove or the piece of granite shown inFigure 11, you can even see the indi-vidual components. In other mixtures,
such as salt water, you cannot see allthe components.
Mixtures Can Be Physically Separated If you don’t likemushrooms on your pizza, you can pick them off. This is aphysical change of the mixture. The identities of the sub-stances did not change. In contrast, compounds can be bro-ken down only through chemical changes.
Not all mixtures are as easy to separate as a pizza. You can-not simply pick salt out of a saltwater mixture, but you canseparate the salt from the water by heating the mixture. Whenthe water changes from a liquid to a gas, the salt remainsbehind. Several common techniques for separating mixturesare shown on the following page.
Figure 11 Colorless quartz, pink feldspar, and black micamake up the mixture granite.
Distillation is a process that separates a mixturebased on the boiling points of the components.Here you see pure water being distilled from asaltwater mixture. In addition to water purifica-tion, distillation is used to separate crude oil intoits components, such as gasoline and kerosene.
A magnet can be used to separate a mixture of the
elements iron and aluminum. Iron isattracted to the
magnet, but aluminum is not.
The components that make up blood are separated using a machine called a centrifuge. This machine separates mixtures according to the densities of the components.
A mixture of the compoundsodium chloride (table salt)with the element sulfur requiresmore than one separation step.
The first step is to mix themwith another compound—water. Salt dissolves in water,but sulfur does not.
In the second step, the mix-ture is poured through a filter.The filter traps the solid sulfur.
In the third step, the sodiumchloride is separated from thewater by simply evaporatingthe water.
The Components of a Mixture Do Not Have a DefiniteRatio Recall that a compound has a specific mass ratio of theelements that form it. Unlike compounds, the components ofa mixture do not need to be combined in a definite ratio. Forexample, granite that has a greater amount of feldspar thanmica or quartz appears to have a pink color. Granite that hasa greater amount of mica than feldspar or quartz appears black. Regardless of which ratio is present, this combination ofmaterials is always a mixture—and it is always called granite.
Air is a mixture composed mostly of nitrogen and oxygen,with smaller amounts of other gases, such as carbon dioxideand water vapor. Some days the air has more water vapor, oris more humid, than on other days. But regardless of the ratioof the components, air is still a mixture.The chart at left sum-marizes the differences between mixtures and compounds.
SolutionsA solution is a mixture that appears to be a single substancebut is composed of particles of two or more substances thatare distributed evenly amongst each other. Solutions are oftendescribed as homogeneous mixtures because they have the sameappearance and properties throughout the mixture.
The process in which particles of substances separate andspread evenly throughout a mixture is known as dissolving. Insolutions, the solute is the substance that is dissolved, and thesolvent is the substance in which the solute is dissolved. Asolute is soluble, or able to dissolve, in the solvent. A substancethat is insoluble, or unable to dissolve, forms a mixture that isnot homogeneous and therefore is not a solution.
Salt water is a solution. Salt is soluble in water, meaningthat salt dissolves in water. Therefore, salt is the solute andwater is the solvent. When two liquids or two gases form asolution, the substance with the greater volume is the solvent.
Chapter 492
Mixtures vs. Compounds
Mixtures
Componentsare elements,compounds, or both
Componentskeep theiroriginal properties
Separated by physicalmeans
Formed usingany ratio ofcomponents
Compounds
Componentsare elements
Componentslose their origi-nal properties
Separated by chemicalmeans
Formed usinga set massratio of components
Many substances are solu-ble in water, including salt,sugar, alcohol, and oxygen.Water does not dissolveeverything, but it dissolvesso many different solutesthat it is often called theuniversal solvent.
REVIEW
1. What is a mixture?
2. Is a mixture separated by physical or chemical changes?
3. Applying Concepts Suggest a procedure to separate ironfilings from sawdust. Explain why this procedure works.
You may think of solutions as being liquids. And, in fact,tap water, soft drinks, gasoline, and many cleaning suppliesare liquid solutions. However, solutions may also be gases,such as air, and solids, such as steel. Alloys are solid solutionsof metals or nonmetals dissolved in metals. Brass is an alloyof the metal zinc dissolved in copper. Steel, including thatused to build the Titanic, is an alloy made of the nonmetalcarbon and other elements dissolved in iron. Look at the chartbelow for examples of the different states of matter used assolutes and solvents in solutions.
Particles in Solutions Are Extremely Small The particlesin solutions are so small that they never settle out, nor canthey be filtered out of these mixtures. In fact, the particles areso small, they don’t even scatter light. Look at Figure 12 andsee for yourself. The jar on the left contains a solution ofsodium chloride in water. The jar on the right contains a mix-ture of gelatin in water.
93
Figure 12 Both of these jarscontain mixtures. The mixture inthe jar on the left, however, is asolution. The particles in solu-tions are so small they don’tscatter light. Therefore, you can’tsee the path of light through it.
Self-CheckYellow gold is an alloymade from equal partscopper and silver com-bined with a greateramount of gold.Identify each compo-nent of yellow gold asa solute or solvent.(See page 724 to checkyour answer.)
Gas in gas Dry air (oxygen in nitrogen)
Gas in liquid Soft drinks (carbon dioxide in water)
Concentration: How Much Solute Is Dissolved? A meas-ure of the amount of solute dissolved in a solvent is concentration. Concentration can be expressed in grams ofsolute per milliliter of solvent. Knowing the exact concentra-tion of a solution is very important in chemistry and medi-cine because using the wrong concentration can be dangerous.
Solutions can be described as being concentrated or dilute.Look at Figure 13. Both solutions have the same amount ofsolvent, but the solution on the left contains less solute thanthe solution on the right. The solution on the left is dilutewhile the solution on the right is concentrated. Keep in mindthat the terms concentrated and dilute do not specify the amountof solute that is actually dissolved. Try your hand at calculat-ing concentration and describing solutions as concentrated ordilute in the MathBreak at left.
A solution that contains all the solute it can hold at a giventemperature is said to be saturated. An unsaturated solution con-tains less solute than it can hold at a given temperature. Moresolute can dissolve in an unsaturated solution.
Solubility: How Much Solute Can Dissolve? If you addtoo much sugar to a glass of lemonade, not all of the sugarcan dissolve. Some of the sugar collects on the bottom of theglass. To determine the maximum amount of sugar that candissolve, you would need to know the solubility of sugar. Thesolubility of a solute is the amount of solute needed to makea saturated solution using a given amount of solvent at a cer-tain temperature. Solubility is usually expressed in grams ofsolute per 100 mL of solvent. Figure 14 on the next page showsthe solubility of several different substances in water at dif-ferent temperatures.
Chapter 494
Figure 13 The dilute solution on the left contains less solute than the concentrated solution on the right.
Calculating ConcentrationMany solutions are colorless.Therefore, you cannot alwayscompare the concentrations ofsolutions by looking at thecolor—you have to comparethe actual calculated concen-trations. One way to calculatethe concentration of a liquidsolution is to divide the gramsof solute by the milliliters ofsolvent. For example, the con-centration of a solution inwhich 35 g of salt is dissolvedin 175 mL of water is
�17535
mgL
swal
atter� � 0.2 g/mL
Now It’s Your TurnCalculate the concentrationsof each solution below.Solution A has 55 g of sugardissolved in 500 mL of water.Solution B has 36 g of sugardissolved in 144 mL of water.Which solution is the moredilute one? Which is themore concentrated?
Unlike the solubility of most solids in liquids, the solubil-ity of gases in liquids decreases as the temperature is raised.Bubbles of gas appear in hot water long before the water beginsto boil. The gases that are dissolved in the water cannot remaindissolved as the temperature increases because the solubilityof the gases is lower at higher temperatures.
What Affects How Quickly Solids Dissolve in Liquids?Many familiar solutions are formed when a solid solute isdissolved in water. Several factors affect how fast the solidwill dissolve. Look at Figure 15 to see three methods used tomake a solute dissolve faster. You can see why you will enjoya glass of lemonade sooner if you stir granulated sugar intothe lemonade before adding ice!
Elements, Compounds, and Mixtures 95
Figure 15 Mixing, heating, and crushing iron(III) chlorideincrease the speed at which it will dissolve.
200
240
160
120
80
40
0 80 10020 40 60
Temperature (ºC)
Solu
bilit
y (g
/100
mL
of w
ater
)
Sodium chloride
Sodium nitrate
Cerium sulfate
Potassium bromide
Sodium chlorate
Figure 14 Solubility of Different Substances
The solubility of most solids increases as thetemperature gets higher. Thus, more solute can dissolve at higher temperatures. However,some solids, such as cerium sulfate, are lesssoluble at higher temperatures.
Mixing by stirring or shakingcauses the solute particles to separate from one another andspread out more quickly amongthe solvent particles.
Heating causes particles tomove more quickly. The solventparticles can separate the soluteparticles and spread them outmore quickly.
Crushing the solute increasesthe amount of contact betweenthe solute and the solvent. Theparticles of solute mix with thesolvent more quickly.
Blood is a suspension. The sus-pended particles, mainly red bloodcells, white blood cells, and platelets,are actually suspended in a solutioncalled plasma. Plasma is 90 percentwater and 10 percent dissolvedsolutes, including sugar, vitamins,and proteins.
SuspensionsWhen you shake up a snow globe, youare mixing the solid snow particleswith the clear liquid. When you stopshaking the globe, the snow parti-cles settle to the bottom of the globe.This mixture is called a suspension.A suspension is a mixture in whichparticles of a material are dispersedthroughout a liquid or gas but arelarge enough that they settle out.The particles are insoluble, so theydo not dissolve in the liquid or gas.Suspensions are often described asheterogeneous mixtures because thedifferent components are easily seen.Other examples of suspensions includemuddy water and Italian salad dressing.
The particles in a suspension are fairly large, and theyscatter or block light. This often makes a suspension difficultto see through. But the particles are too heavy to remainmixed without being stirred or shaken. If a suspension isallowed to sit undisturbed, the particles will settle out, as ina snow globe.
A suspension can be separated by passing it through a filter.The liquid or gas passes through, but the solid particles arelarge enough to be trapped by the filter, as shown in Figure 16.
Figure 16 Dirty air is a suspension that could damagea car’s engine. The air filter ina car separates dust from airto keep the dust from gettinginto the engine.
Chapter 496
Shake Well Before Use
Many medicines, such as reme-dies for upset stomach, are sus-pensions. The directions on thelabel instruct you to shake thebottle well before use. Why mustyou shake the bottle? What prob-lem could arise if you don’t?
ColloidsSome mixtures have properties of both solutionsand suspensions. These mixtures are known ascolloids (KAWL OYDZ). A colloid is a mixture inwhich the particles are dispersed throughoutbut are not heavy enough to settle out. Theparticles in a colloid are relatively small and arefairly well mixed. Solids, liquids, and gases can beused to make colloids. You might be surprised atthe number of colloids you encounter each day. Milk,mayonnaise, stick deodorant—even the gelatin andwhipped cream in Figure 17—are colloids. The materi-als that compose these products do not separatebetween uses because their particles do not settle out.
Although the particles in a colloid are much smaller thanthe particles in a suspension, they are still large enough to scat-ter a beam of light shined through the colloid, as shown inFigure 18. Finally, unlike a suspension, a colloid cannot be sepa-rated by filtration. The particles are small enough to passthrough a filter.
Elements, Compounds, and Mixtures 97
Figure 17 This dessert
includes two delicious exam-
ples of colloids—fruity gelatin and
whipped cream.
1. List two methods of making a solute dissolve faster.
2. Identify the solute and solvent in a solution made from15 mL of oxygen and 5 mL of helium.
3. Comparing Concepts What are three differences betweensolutions and suspensions?
REVIEW
Make a colloid found in yourkitchen on page 643 of the
LabBook.
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TOPIC: MixturesGO TO: www.scilinks.orgsciLINKS NUMBER: HSTP095
Figure 18 The particles in the col-loid fog scatter light, making it dif-ficult for drivers to see the roadahead.
Chapter Highlights
Chapter 498
SECTION 1 SECTION 2
Skills Check
SECTION 2
Vocabularyelement (p. 82)
pure substance (p. 82)
metals (p. 85)
nonmetals (p. 85)
metalloids (p. 85)
Section Notes
• A substance in which all theparticles are alike is a puresubstance.
• An element is a pure sub-stance that cannot be bro-ken down into anythingsimpler by physical orchemical means.
• Each element has a uniqueset of physical and chemicalproperties.
• Elements are classified asmetals, nonmetals, ormetalloids, based on theirproperties.
Vocabularycompound (p. 86)
Section Notes
• A compound is a pure sub-stance composed of two ormore elements chemicallycombined.
• Each compound has aunique set of physical andchemical properties that aredifferent from the propertiesof the elements that com-pose it.
• The elements that form acompound always combinein a specific ratio accordingto their masses.
• Compounds can be brokendown into simpler sub-stances by chemicalchanges.
LabsFlame Tests (p. 640)
Visual UnderstandingTHREE CATEGORIES OF ELEMENTSElements are classified as metals,nonmetals, or metalloids, based ontheir properties. The chart on page 85provides a summary of the properties that distinguish each category.
SEPARATING MIXTURES Mixtures can beseparated through physical changes based ondifferences in the physical properties of theircomponents. Review the illustrations on page91 for some techniques for separating mixtures.
Math ConceptsCONCENTRATION The concentration of asolution is a measure of the amount of solutedissolved in a solvent. For example, a solutionis formed by dissolving 85 g of sodium nitratein 170 mL of water. The concentration of thesolution is calculated as follows:
Visit the National Science Teachers Association on-lineWeb site for Internet resources related to this chapter. Justtype in the sciLINKS number for more information about thetopic:
TOPIC: The Titanic sciLINKS NUMBER: HSTP080
TOPIC: Elements sciLINKS NUMBER: HSTP085
TOPIC: Compounds sciLINKS NUMBER: HSTP090
TOPIC: Mixtures sciLINKS NUMBER: HSTP095
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KEYWORD: HSTMIX
99Elements, Compounds, and Mixtures
SECTION 3
Vocabularymixture (p. 90)
solution (p. 92)
solute (p. 92)
solvent (p. 92)
concentration (p. 94)
solubility (p. 94)
suspension (p. 96)
colloid (p. 97)
Section Notes
• A mixture is a combinationof two or more substances,each of which keeps its owncharacteristics.
• Mixtures can be separatedby physical means, such asfiltration and evaporation.
• The components of a mix-ture can be mixed in anyproportion.
• A solution is a mixture thatappears to be a single sub-stance but is composed of asolute dissolved in a solvent.Solutions do not settle, can-not be filtered, and do notscatter light.
• Concentration is a measureof the amount of solute dis-solved in a solvent.
• The solubility of a solute is the amount of soluteneeded to make a saturatedsolution using a givenamount of solvent at a certain temperature.
• Suspensions are hetero-geneous mixtures that con-tain particles large enoughto settle out, be filtered, andblock or scatter light.
• Colloids are mixtures thatcontain particles too smallto settle out or be filteredbut large enough to scatterlight.
