Name: Class: Date: ID: A Chapter 2 Assessment Multiple Choice Identify the choice that best completes the statement or answers the question. Complete short answer questions on a separate sheet of paper. 1. Which of these substances is not an element? a. water c. aluminum b. hydrogen d. iron 2. Tap water is a. an element c. a substance b. a compound d. a mixture 3. When a homemade oil-and-vinegar salad dressing is left standing, it separates into layers. The salad dressing is a a. solution c. colloid b. suspension d. compound 4. Which of the following is NOT an example of a physical property? a. density c. hardness b. flammability d. melting point 5. Which material is a poor conductor of heat? a. iron c. wood b. silver d. copper 6. A material that can be hit without shattering is a. viscous c. malleable b. flammable d. hard 7. At room temperature, a substance with a melting point of 40 C is a a. solid c. gas b. liquid d. mixture 8. Which action involves a chemical change? a. making ice cubes c. cutting wrapping paper b. adding sugar to tea d. baking a cake 9. A substance that has little tendency to change into other substances is said to have low a. reactivity c. viscosity b. density d. conductivity 10. Formation of a precipitate is usually evidence of a. the separation of a mixture c. the formation of a mixture b. a chemical change d. a physical change 1
Name: ID: A Short Answer 11. Explain why the properties of a pure substance do not vary from sample to sample. 12. What is the difference between an element and a compound. 13. How does the composition of a mixture of hydrogen and oxygen differ from the compostion of a compound containing hydrogen and oxygen? 14. Suppose all the grains in a sample of sand were exactly the same size. Could the sample still be a heterogeneous mixture? Explain your answer. 15. What allows a mixture to be separated by filteration? 16. Explain why viscosity is classified as a physical property. 17. Based on these piecs of pottery found in Grand Canyon National Park, would you describe pottery as a malleable or brittle material? 18. A sample of copper can be drawn into a thin wire. Is this property of copper a physical property or a chemical property? Explain. 19. Name one physical property and one chemical property of wood. 20. Why is breaking down a compound into its elements considered a chemical change? 21. List one physical change and one chemical change that occur when a candle burns. 22. Suppose you need to identify the material in an object without changing the object in any way. Should you use physical or chemical properties to identify the material? Explain your choice. 23. Ammonia is a compound of hydrogen and nitrogen that dissolves easily in water. Can you comclude that hydrogen and nitrogen dissolve in water? Explain your answer. 24. What information would you need to know about a sample of air before you could classify the sample as a solution, suspension, or colloid? 25. Explain why you cannot use mass or volume alone to identify substances. 26. At room temperature, two white solids have the same density. With just this information, is it possible to conclude that the two solids are the same material? Explain. 27. How could you use density to show that a gold bracelet contains elements other than gold? 2
Name: ID: A 28. Suppose you mix two colorless liquids together and a gree solid settles to the bottom of the container. Explain why you might be confident that a chemical change has taken place. 29. One of the general safety instructions for working in a labortory is to tie back long hair, especially when using a lab burner. From this instruction, what can you infer about the flammability of hair? 30. Why might valueable documents be stored in pure nitrogen instead of in air? Recall that air is a mixture of gases, including nitrogen and oxygen. 31. Explain why painting an iron railing can slow down the rate at which the railing rusts. Paragraph 32. Cheesecloth is a type of cotton cloth used by cooks. Write a paragraph explaining why a cook might wrap a lemon wedge in cheesecloth before squeezing juice from the lemon. What process for separating mixtures is the cook using? 3
ID: A Chapter 2 Assessment Answer Section MULTIPLE CHOICE 1. ANS: A 2. ANS: D 3. ANS: B 4. ANS: B 5. ANS: C 6. ANS: C 7. ANS: A 8. ANS: D 9. ANS: A 10. ANS: B SHORT ANSWER 11. ANS: The properties of a substance are constant because the compostition of a substance does not vary. 12. ANS: A compound can be broken down into simpler substances, but an element cannot. 13. ANS: The relative proportions of hydrogen and oxygen in the mixture can vary. The relative proportions of hydrogen and oxygen in the compound cannot vary. 14. ANS: Grains with identical sizes could contain different substances (which would be suggested by grains having different colors). 15. ANS: Some particles in the mixture are much larger that other particles in the mixture. 16. ANS: The viscosity if a substance can be determined without changing the substance into a different substance. 1
ID: A 17. ANS: Pottery is brittle. 18. ANS: It is a physical property because the composition of copper does not change as its shape changes. 19. ANS: Students are likely to say that the melting of wax is a physical change and the buring of wax is a chemical change. 20. ANS: Because a compound and its elements are different substances, a chemical change has taken place. 21. ANS: Students are likely to say that the melting of wax is a physical cahnge and the burning of wax is a chemical cahnge. 22. ANS: You should use physical properties because in order to determine chemical properties, you must change the material in the object. 23. ANS: No. The properties of a compound do not necessarily match the properties of the elements from which the compound is formed. 24. ANS: Possible questions: Is the air dusty? and Does the air contain water droplets? 25. ANS: Mass and volume are properties that vary from sample to sample of a substance. 26. ANS: No. It is possible for two different substances to have the same density or for a mixture to have the same density of a substance. 2
ID: A 27. ANS: You could measure the density of the bracelet and compare that value to the known density of a substance. 28. ANS: You could have observed two common clues for a chemical change a color change and the formation of a precipitate. 29. ANS: You can infer that hair is flammable. 30. ANS: Nitrogen has a low reactivity compared to oxygen. 31. ANS: The paint prevents the iron from coming in contact with oxygen and water. If the paint flakes off, the iron will start to rust. ESSAY 32. ANS: The cheesecloth acts as a filter. The lemon juice can pass through, but the seeds cannot. 3