Exam 1, Spring 2011 - Version 406 Exam 1 laude (51635) 1...

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Unformatted text preview: Version 406 Exam 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 J K 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 G = H- T S ln parenleftbigg P 2 P 1 parenrightbigg = H vap R parenleftbigg 1 T 1- 1 T 2 parenrightbigg = MRT T b = iK b m T f = iK f m P i = P i i P = summationdisplay i P i q = mc T q = m H G =- RT ln K K = e G RT ln K 2 K 1 = 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 Which of the following equations is untrue for a solution with a pH of 3? 1. [OH ] = K w 10 3 2. [H + ] = 10 3 3. pOH =- log pK w 10 3 correct 4. all of these equations are true 5. pOH =- log K w 10 3 Explanation: pOH =- log[OH ] K w = [OH ][H + ] pOH =- log K w [H + ] =- log K w 10 3 It should be clear that K w , not pK w belongs in the correct expression for pOH. 002 6.0 points Rank the following liquids by their misci- bility in heptane (C 7 H 16 ), from most miscible to least: NH 3 , CH 3 OH, CH 3 CH 2 F, CCl 4 . 1. CH 3 CH 2 F > CH 3 OH > CCl 4 > NH 3 2. NH 3 > CH 3 OH > CH 3 CH 2 F > CCl 4 3. CCl 4 > CH 3 CH 2 F > CH 3 OH > NH 3 correct 4. CH 3 CH 2 F > CCl 4 > CH 3 OH > NH 3 5. CCl 4 > CH 3 CH 2 F > NH 3 > CH 3 OH Explanation: Like dissolves like. Heptane is hydrocar- bon, and thus completely non-polar. Car- bon tetrachloride is most soluble since even though the C-Cl bond are polar, there is no net dipole in the molecule, followed by fluo- roethane, which is polar. Methanol is small and very polar (exhibiting hydrogen bond- ing), and ammonia is the most polar of the Version 406 Exam 1 laude (51635) 2 liquids, and thus least soluble. 003 6.0 points Which of the following is a possible combina- tion of values for H lattice , H hydration and H solution , respectively, for a salt whose dis- solution is endothermic. 1. +550 ,- 480 , and + 1030 kJ mol 1 , 2.- 900 ,- 900 , and- 1800 kJ mol 1 , 3.- 450 , +400 , and- 50 kJ mol 1 , 4. +640 ,- 620 , and + 20 kJ mol 1 , cor- rect Explanation: H solution = H lattice + H hydration- the problem stipulates that H solution be positive (endothermic) and this limits the values the other two terms can have. 004 6.0 points A container holds a mixture of acetone and water at 40 C. If acet , the mole fraction of acetone, is 0.1, what is the total vapor pressure? (The equilibrium vapor pressures for pure acetone and pure water at 40 C are roughly 400 torr and 50 torr respectively.) 1. 40 torr 2. 85 torr correct...
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Exam 1, Spring 2011 - Version 406 Exam 1 laude (51635) 1...

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