CHE1 - Version 178 Exam 1 mccord(51620 This print-out...

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Version 178 – Exam 1 – mccord – (51620) 1 This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. McCordCH302 1pm class only - 51620 For water: k f = 1 . 86 C / m k b = 0 . 51 C / m C s , ice = 2 . 09 J/g C C s , water = 4 . 18 J/g C C s , steam = 2 . 03 J/g C Δ H fus = 334J / g Δ H vap = 2260J / g 001 10.0points The critical temperature of a substance is the temperature 1. above which it cannot be converted from a gas to a liquid. correct 2. below which it cannot be converted from a liquid to a gas. 3. above which it cannot be converted from a solid to a liquid. 4. below which it cannot be converted from a liquid to a solid. Explanation: 002 10.0points Rank the following in terms of decreas- ing miscibility in C 8 H 18 (octane): C 2 H 5 Cl (chloroethane), H 2 O (water), C 2 H 5 F (fluo- roethane), C 9 H 20 (nonane). 1. C 2 H 5 F > H 2 O > C 9 H 20 > C 2 H 5 Cl 2. C 9 H 20 > C 2 H 5 Cl > C 2 H 5 F > H 2 O cor- rect 3. H 2 O > C 9 H 20 > C 2 H 5 Cl > C 2 H 5 F 4. C 2 H 5 Cl > C 2 H 5 F > H 2 O > C 9 H 20 Explanation: Octane is a non-polar solvent and thus ranking in terms of decreasing miscibility re- quires ranking in terms of decreasing non- polar character, i.e. from least to most polar. 003 10.0points Which of the following would decrease the solubility of carbon monoxide gas, CO(g), in the solvent ethanol? I) decreasing the temperature of the sample II) increasing the amount of solvent III) changing to a less polar solvent 1. II only 2. III correct 3. I, II and III 4. I and II 5. I only 6. II and III 7. I and III Explanation: The solubility of a gas is directly propor- tional to the gas’ pressure, inversely propor- tional to the temperature of the solvent. Con- sidering the principle of like dissolve like, a polar species such as CO(g) will be more sol- uble in polar solvents. The volume of the solvent does not impact the solubility, which is an intensive property; this is evident when one considers the unity of solubility such as grams per liter, etc. 004 10.0points What is the functional relationship between temperature and vapor pressure?
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Version 178 – Exam 1 – mccord – (51620) 2 1. Vapor pressure is an unusual physical phenomenon in that it is temperature inde- pendent. 2. As temperature increases, vapor pressure decreases exponentially. 3. As temperature increases, vapor pressure decreases linearly. 4. As temperature increases, vapor pressure increases exponentially. correct 5. As temperature increases, vapor pressure increases linearly. Explanation: Vapor pressure increases exponentially with temperature. 005 10.0points The weak acid HZ (175 g/mol) will ionize somewhat when dissolved in water. 150 mL of solution contains 0 . 82 g of the acid. This solution has an osmotic pressure of 863 torr at a temperature of 300 K. What is the percent ionization of the weak acid HZ?
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