Exam3_HW8-11 - Version 162 Exam 3 Mccord (52445) 1 This...

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Unformatted text preview: Version 162 Exam 3 Mccord (52445) 1 This print-out should have 29 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points What is the pH of a solution in which the concentration of hypochlorous acid is 0.50 M and the concentration of sodium hypochlorite is 1.0 M? ( K a for HOCl = 3 . 2 10 8 .) 1. 8.31 2. 8.10 3. 7.49 4. 7.19 5. 6.89 6. 7.80 correct 7. 5.44 Explanation: [OCl ] = 1.0 M [HOCl] = 0.50 M K a = 3 . 2 10 8 pH = p K a + log parenleftbigg [OCl ] [HOCl] parenrightbigg = log(3 . 2 10 8 ) + log parenleftbigg 1 . . 5 parenrightbigg = 7 . 79588 002 10.0 points Bromcresol green is an acid base indicator and changes from yellow to blue in the pH range of 3.8 to 5.4. Which of the following is the best estimate of the p K a of the indicator? 1. 2.1 2. 4.6 correct 3. 5.4 4. 7.0 5. 9.2 6. It is impossible to even guess without more information. 7. 3.8 Explanation: The p K a for an indicator is usually centered in the middle of its pH range. The center of this range is 4.6. 003 10.0 points For the reduction of Cu 2+ by Zn, G = 212 kJ/mol and E = +1.10 V. If the coefficients in the chemical equation for this reaction are multiplied by 2, G = 424 kJ/mol. This means E = +2.20 V. 1. False correct 2. True Explanation: 004 10.0 points Below is the pH curve for a titration of a weak base with 0.10 M HCl. What is the p K b of the weak base? 1. 4.6 correct 2. 11.3 3. 7.00 4. 8.7 Version 162 Exam 3 Mccord (52445) 2 5. 2.7 6. 5.3 7. 9.4 Explanation: The end point is at 60 mL which makes the half way point 30 mL. The pH at this point is at 9.4 which will be the p K a of the conjugate acid of the weak base. The p K b will be 14 minus the p K a which results in 4.6. 005 10.0 points Choose the effective pH range of a HF NaF buffer. For HF, K a = 3 . 5 10 4 . 1. 0.7 to 2.7 2. 2.5 to 4.5 correct 3. 6.0 to 8.0 4. 9.6 to 11.6 5. 5.0 to 7.0 Explanation: 006 10.0 points Complex ions are readily formed by many transition metal ions and 1. ligands that are good Bronsted-Lowry acids. 2. ligands that have unshared electron pairs. correct 3. ligands that can form a hydrogen bond. 4. ligands that are good Bronsted-Lowry bases. 5. ligands that have unfilled valence or- bitals. Explanation: 007 10.0 points What would be the molar solubility of Cu 2 S ( K sp = 2 10 47 ) in a 2 10 3 M solution of CuNO 3 ? 1. 1 . 10 44 2. 5 . 10 42 correct 3. 1 . 3 10 43 4. 1 . 7 10 16 Explanation: molar solubility = parenleftbigg K sp [ Cu + ] 2 parenrightbigg = parenleftBigg 2 10 47 (2 10 3 ) 2 parenrightBigg = 5 10 42 008 10.0 points What is the oxidation state of the arsenic atom in the arsenite ion, AsO 4 3 ?...
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This note was uploaded on 10/25/2010 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.

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Exam3_HW8-11 - Version 162 Exam 3 Mccord (52445) 1 This...

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