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alex test 1

# alex test 1 - a js999 Exam 1 Holcombe(53570 This print-out...

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ajs999 – 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 Henry’s Law would allow one to predict 1. the extent of dissociation of solute in solution. 2. the vapor pressure of the solvent above the pure solvent. 3. the solubility of a gas in a liquid given the pressure of gas above the solution. correct 4. elevation in boiling point with the addi- tion of a non-volatile solute. 5. the new pressure of a gas if only the volume of the vessel containing the gas were changed. 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. 002 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. 0 0 . 2 0 . 4 0 . 6 0 . 8 1 . 0 0 20 40 60 80 100 120 140 X A boiling temperature ( 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. 3. X A in the beaker will approach 0. 4. X A in the beaker will approach 0.3. cor- rect Explanation: 003 10.0 points Note: Each member of the pair must have the van’t Hoff factor designated below to be the correct answer. Which of the following pairs have a van’t Hoff i factor of 3? 1. glucose and sodium chloride 2. perchloric acid and barium hydroxide 3. sodium sulfate and potassium chloride 4. calcium chloride and potassium sulfate correct 5. magnesium sulfate and ethylene glycol Explanation:

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ajs999 – Exam 1 – Holcombe – (53570) 2 004 10.0 points What is the osmotic pressure of a solution that contains 4.56 × 10 3 moles of lactose in 100 mL of solution at M 25 C? 1. 536 torr 2. 848 torr correct 3. 71 torr 4. 111.5 torr 5. 165.6 torr Explanation: n = 4 . 56 × 10 3 mol V = 100 mL T = 25 C + 273 = 298 K M = parenleftbigg 456 × 10 3 mol 100 mL parenrightbiggparenleftbigg 1000 mL L parenrightbigg = 4 . 56 × 10 2 mol L Osmotic pressure π = M R T = ( 4 . 56 × 10 2 mol / L ) × parenleftbigg 0 . 082 L · atm K · mol parenrightbigg (298 K) × parenleftbigg 760 torr 1 atm parenrightbigg = 844 torr 848 torr 005 10.0 points Which one of the following statements is NOT correct? 1. When Δ H for a reaction is negative the reaction can occur spontaneously. 2. When Δ G for a reaction is positive the reaction cannot occur spontaneously. 3. When Δ G for a reaction is zero the system is at equilibrium. 4. When Δ H for a reaction is positive the re- action cannot occur spontaneously. correct 5. When Δ G for a reaction is negative the reaction can occur spontaneously. Explanation: When Δ G is negative, the process is spon- taneous. When Δ G = 0, the process is at equilibrium. When Δ G is positive, the pro- cess is nonspontaneous. The sign of Δ H has no general definite effect on spontaneity since Δ G = Δ H - T Δ S . Δ G is dependent on Δ H and T Δ S .
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alex test 1 - a js999 Exam 1 Holcombe(53570 This print-out...

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