Exam 1 - Version 111 Exam 1 Holcombe (52460) This print-out...

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Version 111 – 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 Consider the temperature composition dia- grams oF two di±erent binary mixtures, but each containing A as one oF the compo- nents. Which curve best describes the sit- uation where the more volatile component oF the mixture CAN be initially collected in the pure Form in the distillate iF X A in the boiling pot = 0.5? 1. 0 0 . 2 0 . 4 0 . 6 0 . 8 1 . 0 0 20 40 60 80 100 120 140 X A boiling temperature ( C) correct 2. Neither diagram 3. 0 0 . 2 0 . 4 0 . 6 0 . 8 1 . 0 0 20 40 60 80 100 120 140 X A Explanation: 002 10.0 points What mass oF ethylene glycol ((CH 2 OH) 2 with molecular weight 62 g/mol) must be added to 1.00 L oF H 2 O (oF mass 1 kg) to lower the Freezing point to - 5 C? K f H 2 O = 1 . 86 C /m . 1. 123 g 2. 25 g 3. 167 g correct 4. 66 g 5. 330 g Explanation: MW CH 2 OH = 62 g/mol V H 2 O = 1 L m H 2 O = 1 kg T f = - 5 C T f = T 0 f - Δ T f Δ T f = T 0 f - T f = 0 . 00 C - ( - 5 C) = 5 C Δ T f = K f · m m = Δ T f K f = 5 C 1 . 86 C /m = 2 . 688 m
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Version 111 – Exam 1 – Holcombe – (52460) 2 m = n (CH 2 OH) 2 kg water = g (CH 2 OH) 2 MW (CH 2 OH) 2 kg water g (CH 2 OH) 2 = m (MW (CH 2 OH) 2 )(kg water) = 2 . 688 mol (CH 2 OH) 2 kg water × 62 . 0 g (CH 2 OH) 2 mol (CH 2 OH) 2 × (1 kg water) = 167 g (CH 2 OH) 2 003 10.0 points 57 . 9 g sodium nitrate is dissolved in water to make 701 g of solution. What is the percent sodium nitrate in the solution? 1. 0 . 0825963% 2. 8 . 25963% correct 3. 100% 4. 9 . 00327% Explanation: m NaNO 3 = 57 . 9 g m soln = 701 g percent = mass solute mass solution × 100 % = 57 . 9 g NaNO 3 701 g solution × 100 % = 8 . 25963% 004 10.0 points The chemical reaction 2 H 2 O + energy 2 H 2 + O 2 is 1. an endothermic reaction. correct 2. an exothermic reaction. 3. an ionic reaction. 4. a synthesis reaction. Explanation: Energy is required to start the reaction. 005 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. 124 torr 3. 61.5 torr 4. 71.7 torr correct 5. 51.3 torr Explanation: 006 10.0 points The colligative eFects of 1 molal sugar solu- tion would be ? 1 molal sodium chloride solution. 1. greater than 2. the same as 3. less than correct Explanation: Sugar is a non-electrolyte so the concen- tration of particles is the concentration of dissolved sugar. Soduim chloride is an electrolyte which dis-
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This note was uploaded on 09/27/2010 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.

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Exam 1 - Version 111 Exam 1 Holcombe (52460) This print-out...

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