# 2_new - Homework#2 holcombe(51160 This print-out should...

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Homework #2 holcombe (51160) 1 This print-out should have 22 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Consider two closed containers. Container X is a 2 L container that contains 0.5 L of acetone. Container Y is a 2 L container that contains 1.8 L of acetone. Both containers and contents are at 30 C. Which of the following is true? 1. The vapor pressure in container X is greater. 2. The vapor pressures in both containers are equal. correct 3. The vapor pressure in container Y is greater. 4. You would need information about the shape of the containers to be able to answer this question. Explanation: 002 10.0 points Which of the following is a restatement of Henry’s Law? 1. Heating a solution will decrease the solu-bility of gases dissolved in it. 2. A mixture of two liquids will have a vapor pressure that isn’ t equal to either of the pure liquid’s vapor pressures. 3. Adding a non-volatile solute to a liquid will lower its vapor pressure. 4. As the partial pressure of a gas above a liquid increases, the gas’s solubility in that liquid also increases. correct Explanation: Henry’s law, formulated by William Henry is 1803 states: ”At a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly propor-tional to the partial pressure of that gas in equilib rium with that liquid.” 003 10.0 points The vapor pressures of pure carbon disulfide and carbon tetrachloride are 360 and 99.8 torr, respectively, at 296 K. What is the vapor pressure of a solution containing 50.0 g of each compound? 1. 241 torr 2. 460 torr 3. 260 torr 4. 33.0 torr 5. 274 torr correct Explanation: 004 10.0 points For gases that do not react chemically with water, the solubility of the gas in water gen- erally (decreases, increases) with an increase in the pressure of the gas and (decreases, in- creases) with increasing temperature. 1. decreases; decreases 2. increases; increases 3. increases; decreases correct 4. decreases; increases Explanation: An increase in pressure means that you have increased the concentration of gas above the solvent surface, thereby increasing the concentration of the gas in the solvent. In-creasing the temperature will decrease the solubility of the gas. 005 10.0 points The vapor pressure of pure CH 2 Cl 2 (molecu- lar weight = 85 g/mol) is 133 torr at 0 C and the vapor pressure of pure CH 2 Br 2 (molecu-

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Homework #2 holcombe (51160) 2 lar weight 174 g/mol) is 11 torr at the same temperature. What is the total vapor pres- sure of a solution prepared from equal masses of these two substances? 1. vapor pressure = 93 torr correct 2. vapor pressure = 105 torr 3. vapor pressure = 72 torr 4. vapor pressure = 124 torr 5. vapor pressure = 144 torr 6. vapor pressure = 89 torr Explanation: For CH 2 Cl 2 , P 0 = 133 torr MW = 85 g/mol For CH 2 Br 2 , P 0 = 11 torr MW = 174 g/mol This is a combination of Raoult’s Law and Dalton’s Law of Partial Pressures. The an - swer does not depend on what the masses are, as long as they are equal. You can choose any mass you like, but to speed up
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