Exam 1-solutions

# Exam 1-solutions - acm2258 – Exam 1 – Holcombe...

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Unformatted text preview: acm2258 – Exam 1 – Holcombe – (53570) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. R = 8 . 314 J/mol K R = 0 . 08206 L atm/mol K 1 atm = 760 torr = 101.325 kPa 001 10.0 points The vapor pressure of the solvent above a solution is directly proportional to 1. the molarity of the solvent in the solu- tion. 2. the molality of the solute in the solution. 3. the molality of the solvent in the solu- tion. 4. the molarity of the solute in the solution. 5. the temperature in Kelvins. 6. the temperature in degrees Celsius. 7. the mole fraction of the solute in the solution. 8. the mole fraction of the solvent in the solution. correct Explanation: Raoult’s Law states P solvent = X solvent P solvent where P solvent is the vapor pressure above a solution, X solvent is the mole fraction of the solvent, and P solvent is the vapor pressure of the pure solvent. As the mole fraction in- creases, the vapor pressure above the solution increases; i . e . , they are directly proportional. 002 10.0 points Henry’s Law would allow one to predict 1. the extent of dissociation of solute in solution. 2. the solubility of a gas in a liquid given the pressure of gas above the solution. correct 3. the new pressure of a gas if only the volume of the vessel containing the gas were changed. 4. elevation in boiling point with the addi- tion of a non-volatile solute. 5. the vapor pressure of the solvent above the pure solvent. Explanation: Henry’s law states that the pressure of a gas above the surface of a solution is proportional to the concentration of gas dissolved in the solution. 003 10.0 points Consider the temperature composition dia- gram of a binary mixture of A and B which forms a minimum boiling azeotrope: Initially X A = 0 . 6. . 2 . 4 . 6 . 8 1 . 20 40 60 80 100 120 140 X A boilingtemperature( ◦ C) Which of the following is true if the distil- late is collected from a distillation apparatus while the solution boils? 1. X A in the beaker will approach 1. 2. X A in the beaker will remain the same. acm2258 – Exam 1 – Holcombe – (53570) 2 3. X A in the beaker will approach 0. 4. X A in the beaker will approach 0.3. cor- rect Explanation: 004 10.0 points What is the vapor pressure at 100 ◦ C of a solution containing 0 . 545 moles of a solute in 3 . 86 moles of water? The solute does not ionize, it is not volatile, and you may consider the solution to be ideal. The vapor pressure of water at 100 ◦ C is 760 torr. 1. 642 . 5 torr 2. 678 . 8 torr 3. 698 torr 4. 666 torr correct 5. 652 . 7 torr 6. 691 . 1 torr 7. 685 . 2 torr Explanation: n solute = 0 . 545 mol n water = 3 . 86 mol P water = 760 torr P soln = X water P water = n H 2 O n H 2 O + n solute × P water = parenleftBig 3 . 86 mol 3 . 86 mol + 0 . 545 mol parenrightBig (760 torr) = 666 torr 005 10.0 points The vapor pressure of a liquid at 25 ◦ C is 200 torr. What will happen when the barometrictorr....
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Exam 1-solutions - acm2258 – Exam 1 – Holcombe...

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