What s the difference between a physical property and a chemical property? What is the difference between a physical change and a chemical change?

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1 ALE 5. Classification of Matter Name CHEM 161 K. Marr Team No. Section What s the difference between a physical property and a chemical property? What is the difference between a physical change and a chemical change? The Model (Reference: section 2.1 in Silberberg 5 th ed.) Matter is defined as anything that has mass and takes up space. An atom is the smallest particle of matter that can involve itself in a chemical reaction. (Nuclear reactions involve subatomic particles such as neutrons and/or protons.) All of matter is composed of atoms. Matter can be classified as one of the following: (1) an element; (2) a compound; (3) a homogeneous mixture (also called a solution); or (4) a heterogeneous mixture. Examples of these are given in the figures below. Na Na Na Na Na Na Figure 1. Atoms of the element sodium, Na. This figure represents a slice through a (very small) crystal of a solid sample of sodium metal. Each sodium atom is depicted as a circle around Na. Figure 2. Diatomic molecules of the element chlorine, Cl 2. This diagram represents a freeze frame of a gaseous sample of chlorine molecules moving randomly in a spherical container. A molecule is two or more atoms chemically bonded together in a fixed ratio by mass. Figure 3. Molecules of the compound hydrogen chloride, HCl. This diagram represents a freeze frame of a gaseous sample of hydrogen chloride molecules moving randomly in a spherical container. The chlorine atoms are larger than the hydrogen atoms. ALE 5 - Classification of Matter Fall 2008 Page 1 of 5

2 Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Figure 4. The compound sodium chloride, NaCl. This figure represents a slice through a very small crystal of solid sodium chloride, NaCl. Figure 5. Two homogeneous mixtures of sodium chloride and water. The white circles without Na + represent molecules of water, H 2 O. When NaCl is added to water, water molecules dissolve (separate) the particles of sodium chloride to form a homogeneous mixture (solution). This is a freeze frame all of the particles are in constant random motion. Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Figure 6. A heterogeneous mixture of silver chloride, AgCl and water. The square arrays of Ag + and Cl - represent crystals of solid silver chloride. The empty white circles without represent molecules of water, H 2 O. This is a freeze frame all of the water molecules are in constant random motion. ALE 5 - Classification of Matter Fall 2008 Page 2 of 5

3 Figure 7. The classification of matter into mixtures and pure substances Key Questions 1. What makes one sample of matter an element, another sample a compound, and another a mixture? Distinguish between an element, a compound, a mixture and a pure substance giving an example of each that is not found on this handout. a) element: b) compound: c) mixture: d) pure substance: ALE 5 - Classification of Matter Fall 2008 Page 3 of 5

4 2. Most of the elements are metals, but some of the nonmetallic elements exist naturally as molecular species. Use figures 1 and 2 of the model to compare and contrast the metallic element sodium with the nonmetallic element chlorine. What do they have in common and what is different about them? 3. Are there molecules of sodium chloride within a sodium chloride crystal? Yes or No Circle your choice and explain your reasoning: 4. What is (are) the difference(s) between a homogeneous mixture and a heterogeneous mixture? Give an example of each that is not found on this handout. Exercises 5. Can the relative amounts of the components of a mixture vary? Explain using specific examples to support your explanation. 6. Can the relative amounts of the components of a compound vary? Explain using specific examples to support your explanation. ALE 5 - Classification of Matter Fall 2008 Page 4 of 5

5 7. The tap water found in many areas of the U.S. and other parts of the world leave white deposits when it evaporates. Is this tap water a mixture or a compound? Explain. 8. Explain the following Statements. Support your explanations with appropriate examples. a.) The smallest particles unique to an element may be atoms or molecules. b.) The smallest particles unique to a compound cannot be atoms. Use the following information to answer questions 9-13 Sea water is collected at the beach and found to contain several grains of pure, quartz sand. The mixture is filtered and the solid sand placed in a vial labeled A. Half the remaining liquid is placed in vial B. The other half of the liquid is heated till it boils. The gas that escapes is collected and cooled. The liquid that reforms is placed in vial C. The solid that remains after the boiling is placed in vial D. Use the following four choices to categorize each sample below: a.) pure element b.) pure compound c.) homogeneous mixture d.) heterogeneous mixture 9. The original sample 10. The sample in vial A 11. The sample in vial B 12. The sample in vial C 13. The sample in vial D 14. Categorize each of the following as a pure substance, a homogeneous mixture or heterogeneous mixture. a.) white grape juice c.) water with ice cubes b.) open bottle of beer d.) fresh garden salad 15. If you have a container with hydrogen gas and oxygen gas in it do you have water? Explain why or why not. ALE 5 - Classification of Matter Fall 2008 Page 5 of 5