1 133 2 1 3 13 4 07 correct Explanation 122 g SrOH 2 1 mol 122 g 1 mol SrOH 2 1

1 133 2 1 3 13 4 07 correct explanation 122 g sroh 2

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1. 13.3 2. 1 3. 13 4. 0.7 correct Explanation: 122 g Sr(OH) 2 × 1 mol 122 g = 1 mol Sr(OH) 2 1 mol Sr(OH) 2 10 L H 2 O = 0 . 1 M Sr(OH) 2 Sr(OH) 2 (aq) Sr 2+ (aq) + 2 OH (aq) [OH ] = C b · 2 = 0 . 1M · 2 = 0 . 2M pOH = - log[OH ] = - log(0 . 2) = 0 . 7 023 6.0 points The vapor pressure of pure acetone (CH 3 COCH 3 ) at 30 o C is 240 torr. If salt (NaCl) is dissolved into a sample of acetone until the total vapor pressure of the mixture at 30 o C is 180 torr, what is the mol fraction of acetone? 1. 0.25 2. 0.75 correct 3. 0.2 4. 0.8 Explanation: P = P o acetone · χ acetone χ acetone = P P o acetone χ acetone = 180 240 = 0 . 75 024 6.0 points Which of the following is a possible combina- tion of values for ΔH lattice , ΔH hydration and ΔH solution , respectively, for a salt whose dis- solution is endothermic. 1. +640 , - 620 , and + 20 kJ · mol 1 , cor- rect 2. - 900 , - 900 , and - 1800 kJ · mol 1 , 3. - 450 , +400 , and - 50 kJ · mol 1 , 4. +550 , - 480 , and + 1030 kJ · mol 1 , Explanation: Δ H solution = Δ H lattice + Δ H hydration - the problem stipulates that Δ H solution be positive (endothermic) and this limits the values the other two terms can have. 025 6.0 points What would be the pH of a 0.25 M solution of phenylamine (C 6 H 5 NH 2 ) at room temper- ature? The K b of phenylamine is 4 × 10 10 . 1. 10.5 2. 1 3. 13 4. 5 5. 9 correct Explanation: [OH ] = (K b · C b ) 1 / 2 = (4 × 10 10 · 0 . 25) 1 / 2 = (10 10 ) 1 / 2 = 10 5 pOH = - log[OH ] = - log(10 5 ) = 5 pH = pK w - pOH = 14 - 5 = 9 026 6.0 points According to the given phase diagram for carbon dioxide, what are regions 1, 3 and B respectively? Carbon Dioxide
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Version 295 – Exam 1 – Laude – (52390) 8 3 1 4 2 A B 200 250 300 350 400 10 0 10 1 10 2 10 3 10 4 Pressure, bar Temperature, K 1. solid, liquid, triple point 2. solid, vapor, critical point correct 3. liquid, vapor, critical point 4. solid, liquid, critical point 5. solid, vapor, triple point Explanation: As temperature goes up, gas forms. As tem- perature decreases, solid forms. As pressure increases, solid forms. As pressure decreases, gas forms. Point A is the triple point, and Point B is the critical point. 1 = solid, 2 = liquid, 3 = vapor, 4 = supercritical region 027 6.0 points Nitric oxide, NO, is a toxic chemical pro- duced in automobile engines. O 2 ( g ) + N 2 ( g ) ←→ 2 NO( g ) At 2100 C, K = 0 . 0031 and at 25 C, K = 2 . 5 × 10 32 . ΔH of this reaction is (pos- itive/negative) and it would be best to run an engine as (hot/cold) as possible to reduce emissions of NO. 1. positive, cold correct 2. negative, hot 3. positive, hot 4. negative, cold Explanation: The direct proportionality between temper- ature and K demonstrates that ΔH is positive and to prevent the reaction, the engine should be run as cold as possible. 028 6.0 points An unknown liquid has a vapor pressure of 88 mmHg at 45 C and 39 mmHg at 25 C. What is its heat of vaporization? 1. 2000 kJ / mol 2. 2000 J / mol 3. 32000 kJ / mol 4. 32 kJ / mol correct Explanation: Use the Clausius-Clapeyron Equation. Here, the only thing we don’t know is Δ H vap . ln( P 2 P 1 ) = Δ H vap R ( 1 T 1 - 1 T 2 ) Δ H vap = R ln( P 2 /P 1 ) 1 /T 1 - 1 /T 2 Δ H vap = 32 . 0 kJ / mol 029 6.0 points Which of the following statements regard- ing colligative properties is/are true? I) Pure liquid water exhibits a lower freez- ing point than a solution of magnesium chloride in water.
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  • Fall '07
  • Holcombe
  • Chemistry, Vapor pressure, Vapor, ­ Laude

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