Chemistry 2e 1: Essential Ideas 1.1: Chemistry in Context 1. Explain how you could experimentally determine whether the outside temperature is higher or lower than 0 C (32 F) without using a thermometer. Solution Place a glass of water outside. It will freeze if the temperature is below 0 C. 2. Identify each of the following statements as being most similar to a hypothesis, a law, or a theory. Explain your reasoning. (a) Falling barometric pressure precedes the onset of bad weather. (b) All life on earth has evolved from a common, primitive organism through the process of natural selection. (c) My truck ’s gas mileage has dropped significantly, probably because it ’s due for a tune-up. Solution (a) law (states a consistently observed phenomenon, can be used for prediction); (b) theory (a widely accepted explanation of the origin of species); (c) hypothesis (a tentative explanation, can be investigated by experimentation) 3. Identify each of the following statements as being most similar to a hypothesis, a law, or a theory. Explain your reasoning. (a) The pressure of a sample of gas is directly proportional to the temperature of the gas. (b) Matter consists of tiny particles that can combine in specific ratios to form substances with specific properties. (c) At a higher temperature, solids (such as salt or sugar) will dissolve better in water. Solution (a) law (states a consistently observed phenomenon, can be used for prediction); (b) theory (a widely accepted explanation of the behavior of matter); (c) hypothesis (a tentative explanation, can be investigated by experimentation) 4. Identify each of the underlined items as a part of either the macroscopic domain, the microscopic domain, or the symbolic domain of chemistry. For any in the symbolic domain, indicate whether they are symbols for a macroscopic or a microscopic feature. (a) The mass of a lead pipe is 14 lb. (b) The mass of a certain chlorine atom is 35 amu. (c) A bottle with a label that reads Al contains aluminum metal. (d) Al is the symbol for an aluminum atom. Solution (a) macroscopic; (b) microscopic; (c) symbolic, macroscopic; (d) symbolic, microscopic 5. Identify each of the underlined items as a part of either the macroscopic domain, the microscopic domain, or the symbolic domain of chemistry. For those in the symbolic domain, indicate whether they are symbols for a macroscopic or a microscopic feature. (a) A certain molecule contains one H atom and one Cl atom. (b) Copper wire has a density of about 8 g/cm3. (c) The bottle contains 15 grams of Ni powder. (d) A sulfur molecule is composed of eight sulfur atoms. Solution (a) symbolic, microscopic; (b) macroscopic; (c) symbolic, macroscopic; (d) microscopic 6. According to one theory, the pressure of a gas increases as its volume decreases, because the molecules in the gas have to move a shorter distance to hit the walls of the container. Does this theory follow a macroscopic or microscopic description of chemical behavior? Explain your answer. Solution Microscopic. The behavior is explained in terms of the behavior of microscopic particles (molecules). 7. The amount of heat required to melt 2 lbs of ice is twice the amount of heat required to melt 1 lb of ice. Is this observation a macroscopic or microscopic description of chemical behavior? Explain your answer. Solution Macroscopic. The heat required is determined from macroscopic properties. This resource file is copyright 2019, Rice University. All Rights Reserved. Chemistry 2e 1: Essential Ideas 1.2: Phases and Classification of Matter 8. Why is an object's mass, rather than its weight, used to indicate the amount of matter it contains? Solution An object ’s mass is used because the mass of the object is independent of outside forces on the object (that is, it is an intrinsic property of the object), whereas weight depends on the force of gravity and varies as gravity changes from location to location. 9. What properties distinguish solids from liquids? Liquids from gases? Solids from gases? Solution Liquids can change their shape (flow); solids can ’t. Gases can undergo large volume changes as pressure changes; liquids do not. Gases flow and change volume; solids do not. 10. How does a heterogeneous mixture differ from a homogeneous mixture? How are they similar? Solution Mixtures are defined as systems containing two or more components that can be separated by physical means. When components mix and blend in such a manner that all regions are the same, the system is homogeneous; soft drinks, sugar water, gasoline, brass, and sterling silver are common examples of such mixtures. Most mixtures in the environment and in our experience are not homogeneous. Instead, mixtures such as deposits of rocks and minerals, river water, blood, and fruit salad are heterogeneous. The mixtures are alike in that physical methods, rather than chemical methods, can be used to separate the components. 11. How does a homogeneous mixture differ from a pure substance? How are they similar? Solution The mixture can have a variety of compositions; a pure substance has a definite composition. Both have the same composition from point to point. 12. How does an element differ from a compound? How are they similar? Solution Compounds can be broken down by chemical means, whereas elements cannot be decomposed by chemical changes. They are similar in that they both have properties associated with matter. 13. How do molecules of elements and molecules of compounds differ? In what ways are they similar? Solution Molecules of elements contain only one type of atom; molecules of compounds contain two or more types of atoms. They are similar in that both are comprised of two or more atoms chemically bonded together. 14. How does an atom differ from a molecule? In what ways are they similar? Solution An atom consists of only one particle; a molecule consists of two or more atoms. They are similar in that both are composed of the basic building block in chemistry, the atom. 15. Many of the items you purchase are mixtures of pure compounds. Select three of these commercial products and prepare a list of the ingredients that are pure compounds. Solution Answers will vary. Sample answer: Gatorade contains water, sugar, dextrose, citric acid, salt, sodium chloride, monopotassium phosphate, and sucrose acetate isobutyrate. 16. Classify each of the following as an element, a compound, or a mixture: (a) copper (b) water (c) nitrogen (d) sulfur (e) air (f) sucrose (g) a substance composed of molecules each of which contains two iodine atoms (h) gasoline Solution (a) element; (b) compound; (c) element; (d) element; (e) mixture; (f) compound; (g) element; (h) mixture 17. Classify each of the following as an element, a compound, or a mixture: (a) iron (b) oxygen (c) mercury oxide (d) pancake syrup (e) carbon dioxide (f) a substance composed of molecules each of which contains one hydrogen atom and one chlorine atom (g) baking soda (h) baking powder Solution (a) element; (b) element; (c) compound; (d) mixture; (e) compound; (f) compound; (g) compound; (h) mixture
