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Make up Exam 1-solutions - Version 042 Make up Exam 1...

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Version 042 – Make up Exam 1 – Laude – (52390) 1 This print-out should have 28 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 6.0 points Rank the following liquids in increasing order of solubility in water (H 2 O): CH 3 F, (CH 3 ) 2 NH, CH 3 Cl, CBr 4 . 1. (CH 3 ) 2 NH < CBr 4 < CH 3 Cl < CH 3 F 2. CBr 4 < CH 3 Cl < CH 3 F < (CH 3 ) 2 NH correct 3. CH 3 Cl < CH 3 F < (CH 3 ) 2 NH < CBr 4 4. CH 3 F < (CH 3 ) 2 NH < CBr 4 < CH 3 Cl Explanation: According the axiom that ”like dissolves like,” the least miscible will be the non-polar molecule CBr 4 . The most miscible will be (CH 3 ) 2 NH, which exhibits hydrogen bonding just as water does. Between the two polar molecules, CH 3 F is the more polar and thus the more miscible because of the greater elec- tronegativity difference. 002 6.0 points Which of the following statements is/are always true concerning K w ? I) It gets larger as the temperature in- creases II) It equals 10 14 III) K w = [H + ][OH ] 1. I, II, III 2. II, III 3. I only 4. II only 5. I, III correct 6. III only 7. I, II Explanation: All equilibrium processes are temperature dependent, and because auto-protolysis is en- dothermic, K w increases as temperature in- crease. Thus statement I is true, but state- ment II is only true at room temperature. Statement III is the definition of K w . 003 6.0 points An unknown liquid has a vapor pressure of 88 mmHg at 45 C and a heat of vaporization of 32 kJ / mol, what is its vapor pressure at 55 C? 1. 156 mmHg 2. 127 mmHg correct 3. 61 mmHg 4. 89 . 4 mmHg Explanation: Use the Clausius-Clapeyron Equation. Here, the only thing we don’t know is P 2 . ln parenleftbigg P 2 P 1 parenrightbigg = Δ H vap R parenleftbigg 1 T 1 1 T 2 parenrightbigg ln parenleftbigg P 2 88 parenrightbigg = 32 , 000 8 . 31 parenleftbigg 1 318 1 328 parenrightbigg ln P 2 = 32 , 000 8 . 31 parenleftbigg 1 318 1 328 parenrightbigg + ln 88 P 2 = e 4 . 84 = 127 mmHg 004 6.0 points What would be the pH of a solution of hy- poiodous acid (HOI) prepared by dissolving 144 grams of the acid in 200 mL of pure water (H 2 O)? The Ka of hypoiodous acid is 2 × 10 11 1. 7 2. 13 3. 1
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Version 042 – Make up Exam 1 – Laude – (52390) 2 4. 10 5. 5 correct Explanation: 144 g HOI × 1 mol 144 g = 1 mol HOI 1 mol HOI 0 . 2 L H 2 O = 5 M HOI [H + ] = (K a · C a ) 1 / 2 = (2 × 10 11 · 5) 1 / 2 = (10 10 ) 1 / 2 = 10 5 pH = log[H + ] = log(10 5 ) = 5 005 6.0 points Which of the following would lower the va- por pressure of a sample of water in a closed container? I) decreasing the size of the container II) lowering the container temperature III) removing water from the container 1. I only 2. II and III only 3. I and III only 4. III only 5. I and II only 6. I, II and III 7. II onlt correct Explanation: The size of a container and the amount of the volatile species contained in it are irrel- evant to vapor pressure. Temperature is a strong determinant vapor pressure.
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