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Chapter01 - Solutions for Chapter 1 End-of-Chapter Problems...

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November 2004 ACS Chemistry Chapter 1 suggested solutions 1 Solutions for Chapter 1 End-of-Chapter Problem s Problem 1.1 (a) __P __ Water is clear and colorless. (b) __C __ Some metals react with water to produce hydrogen gas. (c) __P __ Water has a density of 1.0 g·cm –3 at 4 C. (d) __P __ Water boils at 100 C. (e) __C __ Water is the product of a reaction between an acid and a base. (f) __P __ Water is a polar molecule. The distinction between physical and chemical properties is not always clear-cut. Some would classify the polarity of the water molecule as a chemical property, since this property is not apparent to our senses, but is interpreted from various measurements and models of matter. Problem 1.2. Solids Liquids Gases Definite volume? Yes Yes No Definite shape? Yes No No Fixed or changing position of molecules? Fixed Changing Changing Small or large average distance between molecules? Small Small Large Problem 1.3. Solids and liquids are called condensed phases. In both of these phases, molecules are relatively close together and are likely to interact with one another. The molecules in the gas phase, by contrast, are spread apart with significantly less chance for interaction. While the process of condensation usually refers to the production of liquid from the gas (vapor) phase, both liquid and solid phases are termed “condensed phases”. Problem 1.4. (a) (b) Upward pointing arrows (vaporization and melting) represent processes that absorb or require energy. In the energy diagrams in the text, these arrows are shown in red. Downward
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Water: A Natural Wonder Chapter 1 2 ACS Chemistry FROG pointing arrows (condensation and freezing) represent processes that release or give off energy. In the energy diagrams in the text, these arrows are shown in blue. Problem 1.5. Many common substances, including gasoline, rubbing alcohol, and cooking oil are liquid at STP, that is, at one atmosphere (now one bar) pressure and 0 C (273 K). Problem 1.6. Many substances, including the components of the Earth’s atmosphere, nitrogen (N 2 ), oxygen (O 2 ), argon (Ar), carbon dioxide (CO 2 ), and water vapor, are gases at STP. Problem 1.7. When water freezes the volume of the solid is greater than the volume of the liquid. If a closed glass bottle initially filled entirely with water is kept outside at a temperature below the freezing point of water, the water will freeze, expand, and break the bottle. Note that this is what is shown in these pictures from Web Companion , Chapter 1, Section 1.1, page 3, in which a plastic bottle filled with water ruptures when the water freezes: Problem 1.8. (a) If one boils a solution of NaCl (aq) and water, the water will evaporate (vaporize) and the salt will be left behind due to the fact that water has a much lower boiling point than table salt, which is a solid at 100 C. (b) A laboratory distillation apparatus for the separation of a sodium chloride solution is shown here. Boiling the solution evaporates the water, which is condensed in the inner tube of the condenser, and runs down to be collected in the receiving flask. After all the water has boiled away, NaCl (s) remains in the boiling flask.
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