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Unformatted text preview: Version 065 Exam 1 Mccord (52450) 1 This print-out should have 28 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points The colligative effects of 1 molal sugar solu- tion would be ? 1 molal sodium chloride solution. 1. less than correct 2. greater than 3. the same as 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. 002 10.0 points K f = 1.86 C/ m for water. We observe the freezing points of four dif- ferent aqueous solutions as follows: Solution A freezes at- . 10 C; Solution B freezes at- 4 . 00 C; Solution C freezes at- 10 . 00 C; and Solution D freezes at- 13 . 00 C. In each solution, the solute is a non-volatile non-electrolyte. Which solution should be expected to have the highest boiling point? 1. Solution A 2. Solution C 3. Solution D correct 4. Solution B Explanation: 003 10.0 points At 20 C the vapor pressure of dry ice is 56.5 atm. If 10 g of dry ice (solid CO 2 ) is placed in an evacuated 0.25 L chamber at a con- stant temperature of 20 C, will all of the solid sublime? 1. No 2. Only if it is at the triple point 3. Yes correct Explanation: The dry ice will sublime until the pressure is equal to the vapor pressure. There are 0.227 moles of CO 2 . If all sublimes the pressure will be less than the vapor pressure, so the solid will never reach equilibrium with the gas, and the system will be all gas. 004 10.0 points Calculate the number of moles of oxygen that will dissolve in 45 L of water at 20 C if the par- tial pressure of oxygen is 0.21 atm. Henrys constant for oxygen is 0.0013 mol L atm . 1. 0.012 mol correct 2. 0.28 mol 3. 0.00027 mol 4. 0.0013 mol 5. 0.0062 mol Explanation: 005 10.0 points Carbon Dioxide Version 065 Exam 1 Mccord (52450) 2 200 250 300 350 400 10 10 1 10 2 10 3 10 4 Pressure,bar Temperature, K If you start at 10 3 bar and 210 K then isothermally decompress to 1 bar, then iso- barrically heat to 275 K, then isothermally compress to 10 2 bar, how many phase tran- sitions has the system undergone and what state of matter is the CO 2 in? 1. 3, gas 2. 2 gas 3. 3, liquid 4. 2, liquid correct 5. 2, solid 6. 3, supercritical fluid Explanation: The decompression results in crossing the solid-gas phase boundary, and the heating and subsequent compression results in cross- ing the gas-liquid phase boundary. Two total transitions have occurred and the final state is liquid....
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- Spring '07