Forensic chemists test the physical and chemicalproperties of materials found at a crime scene. Theyalso do similar tests on the materials found on asuspect’s skin or clothing. These materials are oftencomplex mixtures, such as soil, which contain manysubstances. In this lab, you will compare the propertiesof three known materials with two samples of“evidence.” These samples represent evidence from acrime scene and evidence from a suspect’s shoe.Although your materials and equipment are lesscomplex than those used by forensic chemists, youroverall method will be similar to the methods they use.

Problem Can the properties of materialsthat appear similar be used to tell them apart?

Materials• 2 spot plates• glass-marking pencil• 5 laboratory spatulas• cornstarch • baking soda• baking powder• wash bottle of water• vinegar• iodine solution• sample from crime scene• sample from suspect’s shoe

Skills Observing, Inferring, Predicting

Procedure

Part A: Properties of Known Substances1. On a separate sheet of paper, copy the data

table shown.

2. Use a glass-marking pencil to label 15 wells Athrough O on the spot plates. Make a marknext to each well, not in the well.

3. Use a spatula to place a small amount of corn-starch in wells A, B, and C. Record any physicalproperties of the cornstarch that you observe.

4. Use a clean spatula to place a small amount ofbaking soda in wells D, E, and F. Record anyphysical properties of baking soda you observe.

5. Using a clean spatula, place a small amount ofbaking powder in wells G, H, and I. Recordany physical properties of baking powderyou observe.

6. Fill wells A, D, and G with water. Record anychanges you observe.

Using Properties to Identify Materials

CornstarchBaking sodaBaking powderCrime scene sampleSample fromsuspect’s shoe

Description Result ofAdding Water

Result ofAdding Vinegar

Sample Result ofAdding Iodine

Data Table

60 Chapter 2

60 Chapter 2

Using Properties Using Properties to Identify MaterialsObjectiveAfter completing this activity, studentswill be able to• identify simple chemical changes. • identify an unknown sample by

comparing its properties to those ofknown materials.

Skills Focus Observing, Inferring,Predicting

Prep Time 10 minutes

Advance Prep Set out small, labeledcontainers of each of the materials to betested for each group. Provide dropperbottles of water, vinegar, and iodinesolution for each group. If you need toprepare iodine solution, mix 1 mL ofconcentrated tincture of iodine with 50 mL of water. Use baking powder forthe crime scene sample and baking sodafor the suspect’s shoe sample.

Class Time 45 minutes

Safety Make sure that students wearaprons, goggles, and plastic disposablegloves throughout the lab. Cautionstudents about the proper handling ofthe iodine solution because it is poison-ous and can stain skin and clothing.Rinse iodine spills with water.

Questioning Strategies Ask students: What observations couldindicate that a chemical change hastaken place? (The release of a gas, theformation of a precipitate, or a colorchange can indicate that a chemicalchange has taken place.) Which testdistinguishes baking soda frombaking powder? (Addition of iodinesolution causes bubbling with bakingpowder, but not with baking soda.) Howcould you use data from this lab tohelp you identify the unknownsamples? (By comparing the test results of the known samples with the test resultsof the unknown samples) Why do youneed to use different wells for eachmaterial? (To avoid contamination ofmaterials being tested)

L2

Sample Data TableSample Description Result of Result of Result of

Adding Water Adding Vinegar Adding Iodine

Cornstarch white powder no change no change blue-black

Baking soda white powder dissolves bubbles no change

Baking powder white powder partly bubbles bubblesdissolves,bubbles

Crime scene white powder partly bubbles bubblessample dissolves,

bubbles

Sample from white powder dissolves bubbles bubblessuspect’s shoe

Properties of Matter 61

7. Fill wells B, E, and H with vinegar. Record anychanges you observe.

8. Add one drop of iodine solution to wells C, F,and I. Record any changes you observe.CAUTION Iodine solution is corrosive andpoisonous. It can stain skin and clothing. Rinseany iodine spills with water.

Part B: Properties of Unknown Substances

9. Predicting Look at the sample from thecrime scene and the sample from the suspect’sshoe. Based on your observations, predictwhether testing will show that the samples areidentical. Record your prediction.

10. Use a clean spatula to place a small amount ofthe sample from the crime scene in wells J, K,and L. Record any physical properties of thesample that you observe.

11. Use a clean laboratory spatula to place a smallamount of the sample from the suspect’s shoein wells M, N, and O. Record any physicalproperties of the sample that you observe.

12. Fill wells J and M with water. Recordyour observations.

13. Fill wells K and N with vinegar. Recordyour observations.

14. Add one drop of iodine solution to wells L and O. Record your observations.

15. Rinse all materials off the spot plates and flushthem down the drain with at least ten times asmuch water. Dispose of your plastic gloves asdirected by your teacher. CAUTION Washyour hands thoroughly with soap or detergentbefore leaving the laboratory.

Analyze and Conclude1. Analyzing Data Were you able to use the

ability to dissolve in water to distinguish allthree materials? Explain.

2. Drawing Conclusions Are the samplesfrom the suspect and from the crimescene identical?

3. Evaluating and Revising Did the data youcollected support your prediction? Explainyour answer.

Design an experiment todetermine the effect of heating

on the materials you tested in this lab. With yourteacher’s approval and supervision, carry out yourexperiment and use the data you collect to identifya sample of an unknown material.

Go Further

Expected Outcome The crime scenesample and the sample from thesuspect’s shoe are not the same. Thecrime scene sample is baking powder and the sample from the suspect’s shoe is baking soda.

Go Further

Check students’ proposed procedures forsafety before permitting them to carryout their experiments. Samples can beplaced on a can lid with safely smoothededges for heating over a Bunsen burneror hot plate. Cornstarch will visibly charwhen heated. The other materials willnot undergo any visible changes.Kinesthetic, Logical

Properties of Matter 61

Analyze and Conclude1. The ability to dissolve in water distinguishedcornstarch from baking soda and baking powder,but not baking soda from baking powder. 2. The results did not indicate that the samplefrom the crime scene (baking powder) has thesame properties as the sample from the suspect’sshoe (baking soda).

3. Yes or no (depending on the predictionmade). Students should use evidence from the water and iodine solution tests to supporttheir answers.Visual, Logical

62 Chapter 2

CHAPTER

2 Study Guide2.1 Classifying Matter

Key Concepts

• Every sample of a given substance has the sameproperties because a substance has a fixed,uniform composition.

• An element has a fixed composition because itcontains only one type of atom.

• A compound always contains two or moreelements joined in a fixed proportion.

• The properties of a mixture can vary because thecomposition of a mixture is not fixed.

• Based on the size of its largest particles, a mixturecan be classified as a solution, a suspension,or a colloid.

Vocabulary

2.2 Physical Properties

Key Concepts

• Viscosity, conductivity, malleability, hardness,melting point, boiling point, and density areexamples of physical properties.

• Physical properties are used to identify a material,to choose a material for a specific purpose, or toseparate the substances in a mixture.

• Filtration and distillation are two commonseparation methods.

Vocabulary

physical property, p. 45

viscosity, p. 45

conductivity, p. 46

malleability, p. 46

melting point, p. 47

boiling point, p. 47

filtration, p. 50

distillation, p. 50

physical change, p. 51

pure substance, p. 39

element, p. 39

atom, p. 39

compound, p. 40

heterogeneousmixture, p. 41

homogeneousmixture, p. 42

solution, p. 42

suspension, p. 43

colloid, p. 44

2.3 Chemical Properties

Key Concepts

• Chemical properties can be observed only whenthe substances in a sample of matter are changinginto different substances.

• Three common types of evidence for a chemicalchange are a change in color, the production of agas, and the formation of a precipitate.

• When matter undergoes a chemical change, thecomposition of the matter changes. When matterundergoes a physical change, the composition ofthe matter remains the same.

Vocabulary

chemical property, p. 54

flammability, p. 54

reactivity, p. 55

chemical change, p. 56

precipitate, p. 57

Concept Map Use information from the chapter tocomplete the concept map below.

Thinking Visually

does notchange during

doeschange during

Compositionof matter

such as such as

melting b. ? rustingc. ?

physicalchange

a. ?

62 Chapter 2

Study Guide

Study TipStructure Study TimeA good way to begin to study for atest is to figure out what topics will becovered and to what extent they willappear on the test. Tell students thatthey should structure their study timeby studying each topic for an amountof time proportionate to its coverage inclass or in the textbook. They should settime goals for themselves and take smallbreaks as a reward for accomplishingeach goal.

Thinking Visuallya. Chemical changeb. Boiling, freezing, crumpling, slicing,braiding, or cuttingc. Burning

Chapter 2

Print• Chapter and Unit Tests, Chapter 2

Test A and Test B• Test Prep Resources, Chapter 2

Technology• Computer Test Bank, Chapter Test 2• Interactive Textbook, Chapter 2• Go Online, PHSchool.com, Chapter 2

Chapter Resources

Properties of Matter 63

CHAPTER

2 Assessment

Choose the letter that best answers the question orcompletes the statement.

1. Which of these substances is not an element?a. water b. hydrogenc. aluminum d. iron

2. Tap water isa. an element. b. a compound.c. a substance. d. a mixture.

3. When a homemade oil-and-vinegar saladdressing is left standing, it separates into layers.The salad dressing is a

a. solution. b. suspension.c. colloid. d. compound.

4. Which of the following is not an example of aphysical property?

a. density b. flammabilityc. hardness d. melting point

5. Which material is a poor conductor of heat?a. iron b. silverc. wood d. copper

6. A material that can be hit without shattering isa. viscous. b. flammable.c. malleable. d. hard.

7. At room temperature, a substance with a meltingpoint of 40ºC is a

a. solid. b. liquid.c. gas. d. mixture.

8. Which action involves a chemical change?a. making ice cubesb. adding sugar to teac. cutting wrapping paperd. baking a cake

9. A substance that has little tendency to changeinto other substances is said to have low

a. reactivity. b. density.c. viscosity. d. conductivity.

10. Formation of a precipitate is usually evidence ofa. the separation of a mixture.b. a chemical change.c. the formation of a mixture.d. a physical change.

Reviewing Content

11. Explain why the properties of a pure substancedo not vary from sample to sample.

12. What is the difference between an element anda compound?

13. How does the composition of a mixture ofhydrogen and oxygen differ from thecomposition of a compound containinghydrogen and oxygen?

14. Suppose all the grains in a sample of sand wereexactly the same size. Could the sample still bea heterogeneous mixture? Explain your answer.

15. What allows a mixture to be separatedby filtration?

16. Explain why viscosity is classified as aphysical property.

17. Based on these pieces of pottery found in GrandCanyon National Park, would you describepottery as a malleable or brittle material?

18. A sample of copper can be drawn into a thinwire. Is this property of copper a physicalproperty or a chemical property? Explain.

19. Name one physical property and one chemicalproperty of wood.

20. Why is breaking down a compound into itselements considered a chemical change?

21. List one physical change and one chemicalchange that occur when a candle burns.

22. Suppose you need to identify the material in anobject without changing the object in any way.Should you use physical or chemical propertiesto identify the material? Explain your choice.

Understanding Concepts

Interactive textbook withassessment at PHSchool.com

Assessment

If your class subscribes tothe Interactive Textbook, your studentscan go online to access an interactiveversion of the Student Edition and aself-test.

Reviewing Content1. a 2. d 3. b4. b 5. c 6. c7. a 8. d 9. a

10. b

Understanding Concepts11. The properties of a substance areconstant because the composition of asubstance does not vary.12. A compound can be broken downinto simpler substances, but an elementcannot.13. The relative proportions of hydrogenand oxygen in the mixture can vary. Therelative proportions of hydrogen andoxygen in the compound cannot vary.14. Grains with identical sizes couldcontain different substances (whichwould be suggested by grains havingdifferent colors).15. Some particles in the mixture aremuch larger than other particles in themixture.16. The viscosity of a substance can bedetermined without changing thesubstance into a different substance.17. Pottery is brittle.18. It is a physical property because thecomposition of copper does not changeas its shape changes.19. Students are likely to say that woodis a poor conductor of heat (physical)and wood is flammable (chemical).20. Because a compound and itselements are different substances, achemical change has taken place.21. Students are likely to say that themelting of wax is a physical change andthe burning of wax is a chemicalchange.22. You should use physical propertiesbecause in order to determine chemicalproperties, you must change thematerial in the object.

Properties of Matter 63

Homework GuideSection

2.12.22.3

Questions1–3, 11–15, 23, 244–7, 16–18, 25–29, 31, 358–10, 19–22, 30, 32–34

64 Chapter 2

CHAPTER

22 Assessment (continued)

23. Applying Concepts Ammonia is a compoundof hydrogen and nitrogen that dissolves easily inwater. Can you conclude that hydrogen andnitrogen dissolve in water? Explain your answer.

24. Posing Questions What information wouldyou need to know about a sample of air beforeyou could classify the sample as a solution,suspension, or colloid?

25. Applying Concepts Explain why you cannotuse mass or volume alone to identify substances.

Use the table to answer questions 26 and 27.

26. Analyzing Data You have a solid with a densityof 0.78 g/cm3. Is it possible that this solid is oneof the substances listed in the table? Explain.

27. Using Tables A solid, rectangular block ofmaterial floats on water. Is it possible that theblock is pure gold? Explain your answer.

28. Drawing Conclusions At room temperature,two white solids have the same density. With justthis information, is it possible to conclude thatthe two solids are the same material? Explain.

29. Designing Experiments How could you usedensity to show that a gold bracelet containselements other than gold?

30. Inferring Suppose you mix two colorless liquidstogether and a green solid settles to the bottomof the container. Explain why you might beconfident that a chemical change has taken place.

Critical Thinking

31. Comparing and ContrastingThe photo shows maple sap beingcollected in a bucket. The sap isabout 97% water and 3% sugarwith traces of other compounds.Cans of 100% pure maple syrupcontain about 34% water and66% sugar. Which would havethe greater viscosity—the maplesap or the maple syrup? Give areason for your answer.

32. Inferring One of the general safety instructionsfor working in a laboratory is to tie back longhair, especially when using a lab burner. Fromthis instruction, what can you infer about theflammability of hair?

33. Applying Concepts Why might valuabledocuments be stored in pure nitrogen instead ofin air? Recall that air is a mixture of gases,including nitrogen and oxygen.

34. Relating Cause and Effect Explain whypainting an iron railing can slow down therate at which the railing rusts.

35. Writing in Science Cheesecloth is a type ofcotton cloth used by cooks. Write a paragraphexplaining why a cook might wrap a lemonwedge in cheesecloth before squeezing juicefrom the lemon. What process for separatingmixtures is the cook using?

Writing in a Journal Keep a journal for a day. Listfive physical changes and five chemical changes thatyou observe. Be sure to describe why you think eachchange is physical or chemical.

Performance-Based Assessment

Concepts in Action

Substance

Aluminum

Table salt

Isopropyl alcohol

Bromine

Water

Gold

Melting Point

660.3°C

800.7°C

�89.5°C

�7.2°C

0.0°C

1064.2°C

Density

2.70 g/cm3

2.17 g/cm3

0.78 g/cm3

3.10 g/cm3

1.00 g/cm3

19.3 g/cm3

Melting Points and Densitiesof Some Substances

For: Self-grading assessment

Visit: PHSchool.com

Web Code: cca-1020

Critical Thinking23. No. The properties of a compounddo not necessarily match the propertiesof the elements from which thecompound is formed. 24. Possible questions: “Is the airdusty?” and “Does the air contain waterdroplets?”25. Mass and volume are properties that vary from sample to sample of asubstance.26. No. Although the density of thesolid matches the density of one of thesubstances in the table, isopropylalcohol is a liquid at room temperature,not a solid.27. No. Gold is too dense to float on water.28. No. It is possible for two differentsubstances to have the same density orfor a mixture to have the same densityof a substance.29. You could measure the density ofthe bracelet and compare that value to the known density of pure gold.30. You would have observed twocommon clues for a chemical change—a color change and the formation of a precipitate.

Concepts in Action31. The syrup has a greater viscositythan the sap because it contains muchless water, which has a low viscosity.32. You can infer that hair is flammable.33. Nitrogen has a low reactivitycompared to oxygen.34. The paint prevents the iron fromcoming in contact with oxygen andwater. If the paint flakes off, the iron willstart to rust.35. The cheesecloth acts as a filter. Thelemon juice can pass through, but theseeds cannot.

Chapter 2

Performance-Based AssessmentAsk students to identify the criteria they used toclassify the changes. Students may observe someevents that will not be easy to classify. Forexample, a student might conclude that achemical reaction occurs when a soft drink can is opened, because bubbles appear.

64 Chapter 2

Your students can independentlytest their knowledge of the chapterand print out their test results foryour files.

Properties of Matter 65

Standardized Test Prep

Choose the letter that best answers the question orcompletes the statement.

1. All pure substances (A) contain only one type of atom.(B) can be broken down into

simpler substances.(C) cannot be broken down into

simpler substances.(D) have a fixed composition. (E) have a variable composition.

2. Which property can be used to separate amixture by distillation? (A) melting point(B) boiling point(C) density(D) viscosity(E) conductivity

3. During which of these events does a chemicalchange occur?(A) Ice cubes melt.(B) A pot of water boils. (C) A heated iron bar turns red.(D) A paper clip is bent.(E) A cake rises in the oven.

4. You can be certain that a change is a chemicalchange if(A) the change cannot be reversed.(B) new substances form.(C) bubbles are produced. (D) a precipitate forms.(E) there is a color change.

Use the drawings to answer Questions 5 and 6.

5. Which of the drawings could represent ahomogeneous mixture?(A) drawing I(B) drawing II(C) drawing III (D) drawings I and III(E) drawings II and III

6. Which of the drawings could representan element?(A) drawing I(B) drawing II(C) drawing III (D) drawings I and III(E) drawings II and III

Test-Taking Tip

Using Models For some test questions, you will be asked todecide what a visual model represents. Look atthe model below. Notice that there are twotypes of particles shown and notice how the par-ticles are distributed. Use what you observe todecide which answer is the best choice.

What type of matter does the model represent?(A) a solution(B) a colloid(C) a suspension(D) an element(E) a homogeneous mixture

(Answer: C)

I II III

Standardized Test Prep1. D 2. B 3. E4. B 5. C 6. A

Properties of Matter 65