# exam 1 - Version 324 – Exam 1 – Holcombe –(52460 This...

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Version 324 – Exam 1 – Holcombe – (52460) 1 This print-out should have 35 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. HelpFul constants and conversions 1 atm = 760 torr = 760 mm Hg 0 degC = 273.15 K R = 8.314 J/K*mol R = 0.082 L*atm/K*mol 001 10.0 points 65 g sodium nitrate is dissolved in water to make 668 g oF solution. What is the percent sodium nitrate in the solution? 1. 100% 2. 10 . 7794% 3. 9 . 73054% correct 4. 0 . 0973054% Explanation: m NaNO 3 = 65 g m soln = 668 g percent = mass solute mass solution × 100 % = 65 g NaNO 3 668 g solution × 100 % = 9 . 73054% 002 10.0 points 30.2 g oF glycerine (C 3 H 8 O 3 ) are dissolved in 150 g oF water. What is the boiling point oF the solution? ( K b oF water = 0.515 C/m) 1. 100.10 C 2. 1.13 C 3. 103.52 C 4. 0.104 C 5. 101.13 C correct Explanation: m C 3 H 8 O 3 = 30.2 g m water = 150 g 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 003 10.0 points The chemical reaction 2 H 2 O + energy 2 H 2 + O 2 is 1. an ionic reaction. 2. an endothermic reaction. correct 3. a synthesis reaction. 4. an exothermic reaction. Explanation: Energy is required to start the reaction. 004 10.0 points 0.0431 moles oF sucrose (a sugar with a MW oF 342 g/mol) are dissolved in 400.0 g oF water. The solution density is 1.013 g/mL and you can assume that the density oF pure water is 1.00 g/mL. What is the molality oF this solution? 1. 0.108 molal correct 2. 0.104 molal 3. 0.0193 molal 4. 0.0271 molal Explanation: 005 10.0 points

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Version 324 – Exam 1 – Holcombe – (52460) 2 What is the form of the equilibrium constant for the process PbO(s) + CO 2 (g) PbCO 3 (s) ? P species means the pressure of species. 1. K p = P PbCO 3 P CO 2 2. K p = 1 P CO 2 correct 3. No other choice is correct. 4. K p = [PbCO 3 ] [PbO] P CO 2 5. K c = [PbCO 3 ] 2 [CO 2 ] [PbO] Explanation: Solids are not included in the K expression. 006 10.0 points K c = 0 . 040 for the system below at 450 C. PCl 5 (g) PCl 3 (g) + Cl 2 (g) Evaluate K p for the reaction at 450 C. 1. 2.4 correct 2. 0.40 3. 5 . 2 × 10 2 4. 6 . 7 × 10 4 5. 0.64 Explanation: R = 0 . 0821 L · atm / mol · K T = 450 C + 273 = 723 K Δ n = n gas products - n gas reactants = 2 - 1 = 1 K p = K c ( RT ) Δ n = (0 . 040)(0 . 0821)(723) = 2 . 37433 007 10.0 points Suppose the reaction A B has an equilibrium constant of 1.0 and the ini- tial concentrations of A and B are 0.5 M and 0.0 M, respectively. Which of the following is the correct value for the Fnal concentration of A? 1. 1.50 M 2. None of these is correct. 3. 0.500 M 4. 0.250 M correct 5. 1.00 M Explanation: K = 1 . 0 [A] ini = 0 . 5 M [B] ini = 0 M A B ini, M 0.5 0.0 Δ, M - x x eq, M 0 . 5 - x x K = [B] [A] = 1 . 0 x 0 . 5 - x = 1 . 0 x = 0 . 25 M [A] = 0 . 5 - x = 0 . 25 M 008 10.0 points Calculate the vapor pressure at 25 C of a mixture of benzene and toluene in which the mole fraction of benzene is 0.650. The vapor pressure at 25 C of benzene is 94.6 torr and that of toluene is 29.1 torr. 1. 84.4 torr 2. 51.3 torr 3. 124 torr
Version 324 – Exam 1 – Holcombe – (52460) 3 4. 61.5 torr 5. 71.7 torr correct Explanation: 009 10.0 points The colligative efects oF 1 molal sugar solu- tion would be ? 1 molal sodium chloride solution.

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exam 1 - Version 324 – Exam 1 – Holcombe –(52460 This...

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