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Unformatted text preview: kad488 – Exam 1 – Lyon – (53565) 1 This print-out should have 23 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. BE SURE THAT YOU HAVE BUB- BLED IN YOUR NAME AND EID COR- RECTLY. WE WILL BE UNABLE TO FIX VERSION NUMBER ERRORS WITH- OUT YOUR EXAM HARDCOPY AND IT WILL TAKE SOME TIME TO MAKE THE CORRECTION. IT MAY BE A WEEK OR MORE BEFORE YOU WILL KNOW YOUR EXAM SCORE IF YOU DO NOT COMPLETE THE BUBBLE SHEET COR- RECTLY. YOU MUST ALSO KEEP YOUR COPY OF THE EXAM AND MAKE IT AVAILABLE IF REQUESTED FOR ANY REASON THIS SEMESTER. 001 10.0 points Which one of the following statements is false? 1. Water dissolves many ionic solutes be- cause of its ability to hydrate ions in solu- tion. 2. Gases are generally more soluble in water under high pressures than under low pres- sures. 3. Gases are generally more soluble in water at high temperatures than at low tempera- tures. correct 4. Carbon tetrachloride (CCl 4 ) is more mis- cible with hexane (C 6 H 14 ) than it is with a polar solvent such as methanol (CH 3 OH). 5. As temperature increases, the solubilities of some solids in liquids increase and the sol- ubilities of other solids in liquids decrease. Explanation: The polarity of water allows it to hydrate the individual ions in the ionic solute. CCl 4 is non-polar and will be miscible with another non-polar liquid and not with a polar one. Increasing temperature makes salts with exothermic Δ H sol more soluble, but salts with endothermic Δ H sol less soluble. Gases are generally more soluble in water under high pressures than under low pressures because of Henry’s Law; as the pressure of a gas above a liquid increases, the concentration of the gas in the solution increases. 002 10.0 points A solution of 0.90 g of an unknown non- electrolyte in 300 mL of water at 27 ◦ C has an osmotic pressure of 38.4 torr. What is the molecular weight of this compound? (Ne- glect volume change due to solute, R = 0.0821 L · atm/mol · K) 1. 4.72 x10 5 g/mol 2. 3 . 78 × 10 2 g/mol 3. 1 . 52 × 10 3 g/mol 4. 1 . 46 × 10 3 g/mol correct 5. 5.81 x10 4 g/mol Explanation: T = 27 ◦ C + 273 = 300 K π = 38 . 4 760 atm π = M RT , where M is molar concentra- tion. M = mol unknown L soln = g unknown / MW unknown L soln g unknown RT = (0 . 90 g) parenleftBig . 08205 L · atm mol K parenrightBig · (300 K) = 22 . 1535 g · L · atm mol MW unknown = g unknown RT π L soln = 22 . 1535 g · L · atm · mol − 1 parenleftBig 38 . 4 760 atm parenrightBig (0 . 300 L) = 1461 . 52 g mol − 1 003 10.0 points kad488 – Exam 1 – Lyon – (53565) 2 Two aqueous solutions are separated by a semipermeable membrane. Solution A = 0.34 M KCl Solution B = 0.64 M KCl Which of the following statements is TRUE?...
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This note was uploaded on 04/27/2008 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.
- Spring '07