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Homework #2-solutions - zakaria(mmz255 Homework#2...

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zakaria (mmz255) – Homework #2 – Holcombe – (52460) 1 This print-out should have 20 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. You would need information about the shape of the containers to be able to answer this question. 2. The vapor pressure in container X is greater. 3. The vapor pressure in container Y is greater. 4. The vapor pressures in both containers are equal. correct 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. As the partial pressure of a gas above a liquid increases, the gas’s solubility in that liquid also increases. correct 4. Adding a non-volatile solute to a liquid will lower its vapor pressure. 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 equilibrium with that liquid.” 003 10.0 points The vapor pressure of a solvent in a solution decreases as its mole fraction decreases. This is known as 1. Raoult’s Law. correct 2. LeChatelier’s Principle. 3. Bragg’s Law. 4. Henry’s Law. Explanation: Raoult’s Law states that the vapor pres- sure of the solvent in a solution equals its mole fraction in the solution times the vapor pressure of the pure solvent. P solvent = X solvent × P 0 solvent 004 10.0 points What is the vapor pressure of carbon disulfide at its normal boiling point? 1. 1.0 atm correct 2. 1.2 atm 3. 2.0 atm 4. 0.5 atm 5. 0.3 atm 6. 2.5 atm Explanation: At ANY liquid’s normal boiling point, the vapor pressure = 1.0 atm. 005 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
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zakaria (mmz255) – Homework #2 – Holcombe – (52460) 2 compound? 1. 260 torr 2. 274 torr correct 3. 241 torr 4. 460 torr 5. 33.0 torr Explanation: 006 10.0 points A decrease in temperature usually (increases, decreases, does not change) the solubility of common salts in water. 1. decreases correct 2. increases 3. does not change Explanation: Most common salts dissolve endothermi- cally in water and therefore their solubility will increase with an increase in temperature.
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