CHAPTER 5 SECTION 3 Mixtures

NameCHAPTER 5ClassDateElements, Compounds, and MixturesSECTION3 MixturesCalifornia ScienceStandardsBEFORE YOU READAfter you read this section, you should be able to answerthese questions:8.7.c How do mixtures differ from elements and compounds? How can mixtures be separated? What are solutions, and how are they characterized?What Are the Properties of Mixtures?The illustration in the figure below shows a familiarmixture—a pizza. When you look at a piece of pizza, youcan easily see different parts that have different properties.A mixture is a combination of two or more substancesthat are not chemically combined.STUDY TIPBrainstorm The main focusof this section is mixturesof substances. Brainstormwords and phrases related tomixtures. Record your workin your notebook.You can see each toppingon this mixture, which isbetter known as a pizza.Chemicals can form mixtures. No chemical changehappens when a mixture is made. That means that eachchemical keeps its same identity. The pepperoni andolives on the pizza don’t change when they are mixed.Making a mixture is therefore a physical change.Sometimes, you can see the components of the mixture. For example, if you mix sugar and sand together,you can see the different crystals in the mixture. In othermixtures, such as salt water, you cannot see the individual parts. Even so, there is no chemical reaction. Youdon’t change the salt or the water by making the mixture.Because the components of a mixture are not changedinto new chemicals, they can often be separated easily.The olives and pepperoni can be picked off the pizza byhand. A magnet can pull iron particles out of a mixture ofiron and sand.Other mixtures are not separated so easily. Salt can’tsimply be picked out of seawater. Salt can be separatedfrom the water in salt water, though, by letting the waterevaporate. Heating the seawater speeds up the process.READING CHECK1. Identify What kindof change occurs when amixture forms?READING CHECK2. Explain Why can mixturesoften be separated easily?Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Reader and Study Guide75Elements, Compounds, and Mixtures

NameSECTION 3ClassDateMixtures continuedTAKE A LOOK3. Identify Distillation alwaysrequires the addition of energyto convert a substance to agas. How is energy added inthe illustration?How Can Mixtures Be Separated?The figure below shows three methods of separatingthe parts of a mixture.Distillation is the process that separates a mixture based on boiling points. Water in this mixtureevaporates and then condenses as pure water.A magnet can be used toseparate a mixture of theelements iron and aluminum.Iron is attracted to the magnet,but the aluminum is not.Critical Thinking4. Infer How does theseparation of blood intoseveral layers in a centrifugeshow that blood is a mixtureinstead of a pure substance?Blood is separated into its parts by a machinecalled a centrifuge. In the test tube of bloodat the left, a layer of plasma rests on top of alayer of red blood cells. A centrifuge separatesmixtures by the densities of the components.Another method of separating the parts of a mixture isto dissolve one of the substances in water, filter the mixture, and then evaporate the water. This is shown belowas a diagram called a flow chart. The flow chart for theseparation of table salt and sulfur is illustrated.TAKE A LOOK5. Identify What is notcollected in the processshown by the flow chart?Dissolving In thefirst step, water isadded, and the mixture is stirred. Saltdissolves in water.Sulfur does not.Filtering In thesecond step, themixture is pouredthrough a filter.The filter traps thesolid sulfur.Evaporating Inthe third step, thewater is evaporated.The salt is left in theevaporating dish onthe hot plate.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Reader and Study Guide76Elements, Compounds, and Mixtures

NameSECTION 3ClassDateMixtures continuedDo Mixtures Have Fixed Ratios?A compound is made of elements that are always present in a fixed ratio. For example, water is always twoparts hydrogen and one part oxygen.A mixture, however, does not have a fixed ratio ofcomponents. If you make a mixture of salt and water,you can put in a little salt or a lot of salt. Either way, youmake a mixture. The figure below compares mixtures andcompounds.MixturesCompoundsare made of elements, compounds,or bothare made of elementskeep the original properties of thecomponentsdo not have the original propertiesof the componentsdo not require heat or electricity forseparation of componentsrequire heat or electricity forseparation of componentsmay have any ratio of componentsmust have a set ratio of componentsREADING CHECK6. Compare How does theratio of components in amixture compare with the ratioof elements in a compound?What Is a Solution?Salt water is an example of a solution. A solution is ahomogeneous mixture. This means that a solution appearsto be a single substance. The particles of the substancesin a solution are evenly spread out. The appearance andproperties are the same throughout the solution.The process in which particles of substances separateand spread evenly throughout a mixture is known asdissolving. In a solution, the component that is presentin the largest amount is called the solvent. Substancespresent in smaller amounts are called solutes.WATER AS A SOLVENTWater is a very common solvent. In a salt watersolution, water is the solvent, and salt is the solute. Wateris the solvent of many of the solutions that you comeacross in daily life. In fact, your body contains manywater solutions—blood plasma, saliva, and tears are allwater solutions. Reactions inside cells take place in watersolutions. So many different substances dissolve in waterthat it is often called the “universal solvent.”Say ItDiscuss Read “What Is aSolution?” Then, in smallgroups, discuss the solventand solutes in soft drinks.READING CHECK7. Identify In a solution,what component is presentin the largest amount?READING CHECK8. Identify What is calledthe universal solvent?Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Reader and Study Guide77Elements, Compounds, and Mixtures

NameSECTION 3ClassDateMixtures continuedTYPES OF SOLUTIONSCritical Thinking9. Apply Ideas If you look atthe side of a quarter, you cansee layers of different metals.Is the coin a solid solution?Explain.Water is not the only solvent, though. Many other liquidsdissolve substances, some of which do not dissolve in water.Hydrocarbon solvents, such as turpentine, are used to dissolvegrease and other substances that don’t dissolve in water.In fact, solvents do not have to be liquids. Gases or evensolids are able to acts as solvents by dissolving other substances. The air around you is a solution of oxygen and othergases in nitrogen. Many familiar metals are alloys. Alloys,such as bronze, are solid solutions in which a metal is thesolvent. Other metal or nonmetal elements are the solutes.The table below shows some examples of solutions.The key point in forming a solution is that the particles ofthe components are evenly spread throughout the solution.Examples of Solutions in Various States of MatterTAKE A LOOK10. Identify In each of theexample solutions, circle thename of the solute.State of matterExampleGas in a gasdry air (oxygen in nitrogen)Gas in a liquidsoft drinks (carbon dioxide in water)Liquid in a liquidantifreeze (an alcohol in water)Solid in a liquidsalt water (salt in water)Solid in a solidbrass (zinc in copper)How Much Solute Can Be Added to a Solvent?READING CHECK11. Define What two thingsdo you need to know in orderto calculate concentration?A measure of the amount of solute in a given amount ofsolvent is concentration. The concentration of a solutiontells the mass of solute in a volume of solution. The unitsof concentration are grams of solute per milliliter of solvent(g/mL). As more solute is added, the concentration of thesolution becomes greater.Solutions are often described as being concentrated ordilute. A dilute solution is one that has a small amountof solute dissolved in the solvent. A concentrated solution has more solute in solution. These terms do not tellyou the actual concentration of the solution. Rather, theydescribe a relative concentration.The dilute solution (left) contains less solute than the concentrated solution (right).Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Reader and Study Guide78Elements, Compounds, and Mixtures

NameClassSECTION 3DateMixtures continuedSOLUBILITYSolubility (g/100 mL of water)Is there a limit to the amount of solute that can beadded to a solution? The answer is yes. Think about howyou add sugar to lemonade. As you add some sugar to thelemonade and stir it, the sugar dissolves. If you add moresugar, you make a solution that is more concentrated.Eventually, no matter how much you stir, some sugarremains as a solid at the bottom of the glass.To find the maximum amount of sugar that you couldadd to the lemonade, you need to know the solubility ofsugar in water. Solubility refers to the ability of a soluteto dissolve in a solvent at a certain temperature.For most solids, the solubility in water increases astemperature increases. This is shown on the graph belowas a line that slopes upward to the right. However, thereare some exceptions. Does the graph show an exceptionto this rule? Yes, the line for cerium sulfate slopes downward to the right. This means that as the temperatureincreases, cerium sulfate gets less soluble.Experiments have determined the solubility of manysubstances in various solvents. The graph below showsthe solubility of several compounds in water.240Critical Thinking12. Infer If you keep addingsugar to lemonade, why doesthe sugar eventually stopdissolving?tehloraum cidoSratem nitSodiu200160120idePotassium brom80Sodium chloride400Cerium sulfate204060Temperature (ºC)80For most solids, solubility increases as temperature increases.Therefore, the amount of solute that can dissolve increasesas the temperature increases. However, some solids, such ascerium sulfate, become less soluble as temperature increases.100Math Focus13. Read a Graph Whatis the solubility of sodiumchlorate at 60 C?Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Reader and Study Guide79Elements, Compounds, and Mixtures

NameClassDateSection 3 Review8.7.cSECTION VOCABULARYconcentration the amount of a particularsubstance in a given quantity of a mixture,solution, or oremixture a combination of two or moresubstances that are not chemically combinedsolubility the ability of one substance todissolve in another at a given temperatureand pressureWordwise The root solute- means “to free” or“to loosen.”solute in a solution, the substance that dissolvesthe solutesolution a homogeneous mixture throughoutwhich two or more substances are dispersedsolvent in a solution, the substance in which thesolute dissolves1. Identify What are the solvent and solute in a solution containing 100 g ofethanol and 3 g of sucrose?2. Organize Complete the Concept Map for a mixture shown below.MixtureHomogeneous mixturePresent in smallest amountPresent in largest amount3. Analyze Processes In a steel factory, iron is melted. Then, other elements, such ascarbon and nickel, are added to the melted iron to make steel. What is the reasonfor melting the iron?4. Apply Concepts Suppose you added a cup of sugar to hot water, and all of thesugar dissolved. Then the water cooled, and some of the sugar was seen as asolid on the bottom of the beaker. Explain why this happened.Copyright by Holt, Rinehart and Winston. All rights reserved.Interactive Reader and Study Guide80Elements, Compounds, and Mixtures

Interactive Reader and Study Guide 77 Elements, Compounds, and Mixtures SECTION 3 Name Class Date Mixtures continued Do Mixtures Have Fixed Ratios? A compound is made of elements that are always pres-ent in a fixed ratio. For example, water is always two parts hydrogen and one part oxyge