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alex hw 3

# alex hw 3 - Version 063 hw03 Holcombe(53570 This print-out...

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Version 063 – hw03 – 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. 001 10.0 points Consider the following pressure diagram for a binary liquid containing A and B. 0 1 x A 20 torr 80 torr If 5 mol of A and 7 mol of B are mixed, what is the vapor pressure of B? 1. 33 torr 2. 80 torr 3. 20 torr 4. 11 torr correct 5. 45 torr Explanation: The mole fraction of A is x A = mol A total mol = 5 mol 5 mol + 7 mol = 0 . 42 . 0 1 0 . 42 80 torr 11 torr 002 10.0 points Occording to Raoult’s Law, a mixture of formic acid (HCOOH) and benzene would show 1. positive deviation. correct 2. no deviation. 3. negative deviation. Explanation: Raoult’s Law applies to the vapor pressure of the mixture, so a positive deviation means that the vapor pressure is higher than ex- pected for an ideal solution and a negative deviation a lower vapor pressure. Negative deviation will occur when the interactions between the different molecules are some- what stronger than the interactions between molecules of the same kind. Because formic acid is a very polar molecule with hydrogen bonding and benzene is non- polar, we would expect a positive deviation, which is observed. Benzene and formic acid form an azeotyope that boils at 71 C, which is well below the boiling point of either benzene (80 . 1 C) or formic acid (101 C). 003 10.0 points Four of the following are colligative properties of solutions. Which one is not a colligative property? 1. vapor pressure lowering 2. freezing point depression 3. molality correct 4. boiling point elevation 5. osmotic pressure Explanation: Colligative properties depend on the num- ber of particles dissolved in the solution, not on the properties of the components. 004 10.0 points During osmosis, which component of a solu- tion is free to move across the semi-permeable

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Version 063 – hw03 – Holcombe – (53570) 2 membrane? 1. the sediment 2. the solvent correct 3. the solute 4. the one with the higher boiling point Explanation: 005 10.0 points Water from a local stream is added to one side of the U-tube shown below. Pure water is placed in the tube on the other side of the semipermeable membrane. With the left side open to barometric pressure of 1.0 atm and 1.5 atm applied to the right side, the two liquids do not move. 1.00 atm 1.15 atm B A In which half of the U-tube is the pure water located? 1. B 2. A correct 3. Not enough information is given. Explanation: 006 10.0 points Two aqueous solutions are separated by a membrane permeable only to water. Solution A is a 0.34 M KCl solution; and Solution B is a 0.64 M KCl solution. Which of the following statements is TRUE? 1. H 2 O molecules flow from solution A to solution B. correct 2. Cl ions flow from solution B to solution A. 3. K + ions flow from solution B to solution A.
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