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Unformatted text preview: Thompson, Margaret – Homework 2 – Due: Sep 18 2007, 11:00 am – Inst: James Holcombe 1 This printout should have 25 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points The temperature at which water boils can be increased by adding some solute, like ethylene glycol. This is known as a colligative property. 1. False 2. True correct Explanation: Colligative properties depend on the num ber of particles dissolved in the solution, not on the properties of the components. This colligative property is the boiling point elevation of water. 002 (part 1 of 1) 10 points The colligative effects of 1 molal sugar solu tion would be ? 1 molal sodium chloride solution. 1. less than correct 2. the same as 3. greater than Explanation: Sugar is a nonelectrolyte so the concen tration of particles is the concentration of dissolved sugar. Soduim chloride is an electrolyte which dis sociates in solution, giving twice as many par ticles as dissolved: NaCl→ Na + + Cl Since colligative properties depend on the number of particles in solution, the colligative effect doubles for the NaCl(aq), compared to any identical concentration of sugar. 003 (part 1 of 1) 10 points The vapor pressure of a volatile component in a solution decreases as its mole fraction decreases. This is known as 1. LeChatelier’s Principle. 2. Bragg’s Law. 3. Raoult’s Law. correct 4. Henry’s Law. Explanation: According to Raoult’s Law, the vapor pres sure of the volatile component of a solution equals its mole fraction in the solution times the vapor pressure of the pure solvent. P = X P 004 (part 1 of 3) 10 points Consider the following pressure diagram for a binary liquid containing A and B. 1 x A 90 torr 30 torr If 800 g of A (100 g / mol) and 1140 g of B (95 g / mol) are mixed, what is the vapor pressure of B? 1. 12 torr 2. 90 torr 3. 65 torr 4. 53 torr correct 5. 30 torr Explanation: We have 800 g 100 g / mol = 8 mol A and 1140 g 95 g / mol = 12 mol B, so the mole fraction Thompson, Margaret – Homework 2 – Due: Sep 18 2007, 11:00 am – Inst: James Holcombe 2 of A is x A = mol A total mol = 8 mol 8 mol + 12 mol = 0 . 4 1 . 4 30 torr 53 torr 005 (part 2 of 3) 10 points What is the corresponding vapor pressure of A? 1. 90 torr 2. 30 torr 3. 65 torr 4. 12 torr correct 5. 53 torr Explanation: 1 . 4 30 torr 12 torr 006 (part 3 of 3) 10 points What is the corresponding total vapor pres sure? 1. 53 torr 2. 12 torr 3. 30 torr 4. 65 torr correct 5. 90 torr Explanation: 1 . 4 30 torr 65 torr 007 (part 1 of 1) 10 points 1,1Dichloroethane (CH 3 CHCl 2 ) has a va por pressure of 228 Torr at 25 ◦ C; at the same temperature, 1,1dichlorotetrafluoroethane (CF 3 CCl 2 F) has a vapor pressure of 79 Torr....
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This note was uploaded on 07/17/2008 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas.
 Spring '07
 Holcombe
 Chemistry

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