finalexam_sutcliffe2 - Version 152 Final sutcliffe (51630)...

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Unformatted text preview: Version 152 Final sutcliffe (51630) 1 This print-out should have 41 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points In the electrolytic refining of copper, the pure copper 1. is electroplated onto the anode. 2. serves as the positive electrode. 3. remains oxidized in solution. 4. serves as the anode. 5. is electroplated onto the cathode. cor- rect Explanation: 002 10.0 points What is the pH of a 0.020 M solution of hydrosulfuric acid, a diprotic acid? K a1 = 1 . 1 10 7 K a2 = 1 . 10 14 1. 3.65 2. 7.00 3. 4.33 correct 4. 5.22 5. 9.67 6. 7.84 7. 4.69 Explanation: Solve using ONLY the 1st ionization. So this works like any other monoprotic acid where the assumption [H + ] = radicalbig (Conc)( K a1 ) is valid. 003 10.0 points What is the pH of a solution labeled 3 10 5 M HBr? 1. 8.7 2. 9.5 3. 5.3 4. 5.5 5. 4.5 correct Explanation: [HBr] = 3 10 5 M HBr is a strong acid which completely ion- izes in aqueous solution. HBr- H + + Br [H 3 O + ] = [HBr] = 3 10 5 M pH =- log[H 3 O + ] = 4 . 52288 004 10.0 points A buffer was prepared by mixing 0.200 mole of ammonia ( K b = 1 . 8 10 5 ) and 0.200 mole of ammonium chloride to form an aqueous solution with a total volume of 500 mL. To 250 mL of this solution was added 50.0 mL of 1.00 M HCl. What is the pH of this solution? 1. 8.38 2. 8.18 3. 8.78 correct 4. 7.87 5. 8.53 6. 9.73 7. 9.35 Explanation: [NH 3 ] = . 2 mol 500 mL [HCl] = 1 . 0 mol 1000 mL [NH + 4 ] = . 2 mol 500 mL [Cl ] = . 2 mol 500 mL K b = 1 . 8 10 5 Version 152 Final sutcliffe (51630) 2 Initial condition (ini): n NH 3 = 250 mL . 2 mol 500 mL = 100 mmol n HCl = 50 mL 1 . 0 mol 1000 mL = 50 mmol n NH + 4 = 250 mL . 2 mol 500 mL = 100 mmol n Cl- = 250 mL . 2 mol 500 mL = 100 mmol NH 3 + HCl NH + 4 + Cl ini, mmol 100 50 100 100 , mmol- 50- 50 50 50 fin, mmol 50 150 150 Cl is a spectator ion. NH + 4 /NH 3 is a buffer system. pH = p K a + log parenleftBigg [NH 3 ] bracketleftbig NH + 4 bracketrightbig parenrightBigg =- log parenleftbigg 1 . 10 14 1 . 8 10 5 parenrightbigg + log parenleftbigg 50 150 parenrightbigg = 8 . 77815 005 10.0 points Which of the following would lower the vapor pressure of a sample of aniline in a closed container? I) adding a non-volatile solute to the liquid II) decreasing the temperature of the sample III) increasing the pressure applied to the outside of the container 1. II only 2. I, II and III 3. I and III 4. II and III 5. I and II correct 6. I only 7. III only Explanation: Because evaporation is always an endother- mic process, a substances vapor pressure al- ways increases with increasing temperature....
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This note was uploaded on 03/26/2012 for the course CHEM 302 taught by Professor Mccord during the Fall '10 term at University of Texas at Austin.

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finalexam_sutcliffe2 - Version 152 Final sutcliffe (51630)...

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