HW 2 Solutions

# HW 2 Solutions - Wright Jacqueline – Homework 2 – Due...

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Unformatted text preview: Wright, Jacqueline – 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. greater than 3. less than correct 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. LeChatelier’s Principle. 2. Henry’s Law. 3. Raoult’s Law. correct 4. Bragg’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 100 torr 60 torr If 4465 g of A (235 g / mol) and 2200 g of B (110 g / mol) are mixed, what is the vapor pressure of B? 1. 60 torr 2. 29 torr 3. 51 torr correct 4. 100 torr 5. 80 torr Explanation: We have 4465 g 235 g / mol = 19 mol A and 2200 g 110 g / mol = 20 mol B, so the mole fraction Wright, Jacqueline – Homework 2 – Due: Sep 18 2007, 11:00 am – Inst: James Holcombe 2 of A is x A = mol A total mol = 19 mol 19 mol + 20 mol = 0 . 49 1 . 49 60 torr 51 torr 005 (part 2 of 3) 10 points What is the corresponding vapor pressure of A? 1. 29 torr correct 2. 80 torr 3. 60 torr 4. 100 torr 5. 51 torr Explanation: 1 . 49 60 torr 29 torr 006 (part 3 of 3) 10 points What is the corresponding total vapor pres- sure? 1. 60 torr 2. 29 torr 3. 80 torr correct 4. 100 torr 5. 51 torr Explanation: 1 . 49 60 torr 80 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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HW 2 Solutions - Wright Jacqueline – Homework 2 – Due...

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