Homework 02 Solutions - Gadhia, Tejas Homework 2 Due: Sep...

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Unformatted text preview: Gadhia, Tejas Homework 2 Due: Sep 18 2007, 11:00 am Inst: James Holcombe 1 This print-out should have 25 questions. Multiple-choice 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. True correct 2. False 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. the same as 2. less than correct 3. greater than 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- 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. Henrys Law. 2. LeChateliers Principle. 3. Raoults Law. correct 4. Braggs Law. Explanation: According to Raoults 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 30 torr 80 torr If 3825 g of A (225 g / mol) and 675 g of B (75 g / mol) are mixed, what is the vapor pressure of B? 1. 52 torr 2. 30 torr 3. 62 torr 4. 10 torr correct 5. 80 torr Explanation: We have 3825 g 225 g / mol = 17 mol A and 675 g 75 g / mol = 9 mol B, so the mole fraction Gadhia, Tejas Homework 2 Due: Sep 18 2007, 11:00 am Inst: James Holcombe 2 of A is x A = mol A total mol = 17 mol 17 mol + 9 mol = 0 . 65 1 . 65 80 torr 10 torr 005 (part 2 of 3) 10 points What is the corresponding vapor pressure of A? 1. 80 torr 2. 30 torr 3. 10 torr 4. 52 torr correct 5. 62 torr Explanation: 1 . 65 80 torr 52 torr 006 (part 3 of 3) 10 points What is the corresponding total vapor pres- sure? 1. 62 torr correct 2. 10 torr 3. 80 torr 4. 52 torr 5. 30 torr Explanation: 1 . 65 80 torr 62 torr 007 (part 1 of 1) 10 points 1,1-Dichloroethane (CH 3 CHCl 2 ) has a va- por pressure of 228 Torr at 25 C; at the same temperature, 1,1-dichlorotetrafluoroethane (CF 3 CCl 2 F) has a vapor pressure of 79 Torr....
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This note was uploaded on 03/19/2011 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.

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Homework 02 Solutions - Gadhia, Tejas Homework 2 Due: Sep...

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