Chem2 hw2s - Yoon Seong Meen – Homework 2 – Due 11:00...

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Unformatted text preview: Yoon, Seong Meen – 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. greater than 2. the same as 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. Bragg’s Law. 2. Henry’s Law. 3. Raoult’s Law. correct 4. LeChatelier’s Principle. 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 70 torr 20 torr If 350 g of A (70 g / mol) and 1100 g of B (110 g / mol) are mixed, what is the vapor pressure of B? 1. 70 torr 2. 46 torr correct 3. 20 torr 4. 6 torr 5. 53 torr Explanation: We have 350 g 70 g / mol = 5 mol A and 1100 g 110 g / mol = 10 mol B, so the mole fraction Yoon, Seong Meen – Homework 2 – Due: Sep 18 2007, 11:00 am – Inst: James Holcombe 2 of A is x A = mol A total mol = 5 mol 5 mol + 10 mol = 0 . 33 1 . 33 20 torr 46 torr 005 (part 2 of 3) 10 points What is the corresponding vapor pressure of A? 1. 70 torr 2. 53 torr 3. 20 torr 4. 6 torr correct 5. 46 torr Explanation: 1 . 33 20 torr 6 torr 006 (part 3 of 3) 10 points What is the corresponding total vapor pres- sure? 1. 53 torr correct 2. 70 torr 3. 6 torr 4. 46 torr 5. 20 torr Explanation: 1 . 33 20 torr 53 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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Chem2 hw2s - Yoon Seong Meen – Homework 2 – Due 11:00...

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