Make up 1-solutions-1 - Version 079 Make up 1 laude(51635...

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Version 079 – Make up 1 – laude – (51635) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. Constants R = 8 . 314 JK 1 mol 1 Definitions Q [C] c [D] d [A] a [B] b G H - TS K w [H + ][OH ] pH ≡- log [H + ] pOH ≡- log [OH ] Equations Δ G = Δ H - T Δ S ln parenleftbigg P 2 P 1 parenrightbigg = Δ H vap R parenleftbigg 1 T 1 - 1 T 2 parenrightbigg Π = MRT Δ T b = iK b m Δ T f = iK f m P i = P i χ i P = summationdisplay i P i q = mc Δ T q = m Δ H Δ G = - RT ln K K = e Δ G RT ln K 2 K 1 = Δ H R parenleftbigg 1 T 1 - 1 T 2 parenrightbigg Q = K [at equil.] [H + ] = ( K a C a ) 1 / 2 [OH ] = ( K b C b ) 1 / 2 [H + ] = K a ( C a /C b ) pH = p K a + log( C b /C a ) [OH ] = K b ( C b /C a ) pOH = p K b + log( C a /C b ) 001 6.0 points Rank following bases from most to least basic: ammonia (NH 3 ) pK b = 4.74 aniline (C 6 H 5 NH 2 ) pK b = 9.42 pyridine (C 5 H 5 N) pK b = 8.77 methylamine (CH 3 NH 2 ) pK b = 3.34 1. NH 3 > C 5 H 5 N > C 6 H 5 NH 2 > CH 3 NH 2 2. C 6 H 5 NH 2 > CH 3 NH 2 > NH 3 > C 5 H 5 N 3. C 5 H 5 N > C 6 H 5 NH 2 > CH 3 NH 2 > NH 3 4. CH 3 NH 2 > NH 3 > C 5 H 5 N > C 6 H 5 NH 2 correct Explanation: The value of pK b is inversely proportional to the basicity (strength) of the base. By ranking from the smallest (3.34) to the small- est (9.42) pK b , one is ranking from the most to least basic. 002 6.0 points Which of the following phase changes is not correctly paired with the sign of its change in enthalpy? 1. vaporization, Δ H is + 2. deposition, Δ H is + correct 3. freezing, Δ H is - 4. condensation, Δ H is - 5. melting, Δ H is + Explanation: Deposition is an exothermic phase change and Δ H is negative. 003 6.0 points Assuming you have a pure sample of water, in which answer choice are all values of K w cor- rectly paired with their corresponding value of [H + ]? A) K w = 1 . 33 × 10 15 B) K w = 1 . 46 × 10 14 C) K w = 1 . 38 × 10 13 1) [H + ] = 1 . 21 × 10 7 2) [H + ] = 3 . 65 × 10 8 3) [H + ] = 3 . 71 × 10 7 1. A1, B2, C3
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Version 079 – Make up 1 – laude – (51635) 2 2. A3, B2, C1 3. A2, B3, C1 4. A3, B1, C2 5. A2, B1, C3 correct 6. A1, B3, C2 Explanation: The proton concentration in a sample of pure water is directly proportional to K w . 004 6.0 points 30 . 2 g of glycerine (C 3 H 8 O 3 , with MW 92 . 1 g / mol) are dissolved in 150 g of wa- ter. What is the boiling point of the solution? ( K b of water = 0 . 515 C / m ) 1. 0.104 C 2. 100.10 C 3. 101.13 C correct 4. 1.13 C 5. 101.52 C Explanation: m glyc = 30 . 2 g MW glyc = 92 . 1 g / mol m water =150 g K b = 0 . 515 C / m Δ T b = K b m = K b mol glycerol kg water = (0 . 515 C /m ) 30 . 2 92 . 1 mol C 3 H 8 O 3 0 . 150 kg water = 1 . 13 C T b = T 0 b + Δ T b = 101 . 13 C 005 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 F < (CH 3 ) 2 NH < CBr 4 < CH 3 Cl 2. CH 3 Cl < CH 3 F < (CH 3 ) 2 NH < CBr 4 3. (CH 3 ) 2 NH < CBr 4 < CH 3 Cl < CH 3 F 4. CBr 4 < CH 3 Cl < CH 3 F < (CH 3 ) 2 NH correct 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
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