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S07 exam 2 - Version 001 Exam 2 David Laude(53015 This...

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Version 001 – Exam 2 – David Laude (53015) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. V1:1, V2:1, V3:1, V4:1, V5:2. Please make sure you write your version numbers on your scantron. Good luck! Strong Acid or Base 22:10, general, multiple choice, < 1 min, fixed. 001 (part 1 of 1) 6 points Which of I) HCl II) HF III) LiOH IV) HClO 2 V) HNO 3 are strong acids or strong bases in water? 1. I, III, and V only correct 2. I, III, IV, and V only 3. I, II, III, and V only 4. All of the compounds 5. I, II, IV, and V only Explanation: Buffer NH3 24:02, general, multiple choice, > 1 min, fixed. 002 (part 1 of 1) 6 points What is the pH of a solution containing 0.3 M NH 4 Cl and 0.6 M NH 3 ? The p K a of the ammonium ion is 9.25. 1. 9.55 correct 2. 8.95 3. 5.05 4. 4.45 5. 12.25 Explanation: Buffer Prep 01 24:02, general, multiple choice, > 1 min, fixed. 003 (part 1 of 1) 6 points Which of the following solutions will produce a buffer? I) 20 mL of 0.5 M (CH 3 ) 3 NHCl + 50 mL of 0.1 M (CH 3 ) 3 N II) 20 mL of 0.5 M HNO 2 + 50 mL of 0.1 M NaOH III) 20 mL of 0.5 M HCl + 50 mL of 0.1 M NH 3 IV) 20 mL of 0.5 M HClO 2 + 50 mL of 0.1 M CH 3 COOH V) 20 mL of 0.5 M NH 4 Cl + 50 mL of 0.1 M NaOH 1. I, II, and V only correct 2. I, II, IV, and V only 3. I, II, III, and V only 4. II and IV only 5. II only Explanation: Msci 18 0412 22:07, general, multiple choice, > 1 min, fixed. 004 (part 1 of 1) 6 points Assume that five weak acids, identified only by numbers (1, 2, 3, 4 and 5), have the follow- ing ionization constants. Ionization Acid Constant K a value 1 1 . 0 × 10 - 3 2 3 . 0 × 10 - 5 3 2 . 6 × 10 - 7 4 4 . 0 × 10 - 9 5 7 . 3 × 10 - 11 The anion of which acid is the weakest base? 1. 1 correct 2. 2 3. 3
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Version 001 – Exam 2 – David Laude (53015) 2 4. 4 5. 5 Explanation: HA * ) H + + A - K a = [H + ] [A - ] [H] [A] The ‘anion of an acid’ is another way of saying ‘conjugate base,’ and a weak conjugate base corresponds to a strong acid. So really what we’re looking for is which acid is strongest (has the lowest pH). A low pH means that the [H + ] concentra- tion is low. (Remember that values greater than 7 are basic!) The larger values of K a means that there is more [H + ] so you would expect these solutions to be more acidic; i.e., have smaller pH’s. The smaller K a values mean less [H + ] in solution, so higher pH’s. The acid with the largest K a (#1) will have the lowest pH; i.e., highest [H + ] concentration Buffer Capacity 01 24:04, general, multiple choice, > 1 min, fixed. 005 (part 1 of 1) 6 points What is the buffer capacity of 50 mL of 0.3 M HNO 2 and 100 mL of 0.5 M NaNO 2 ? 1. 0.015 mol of OH - and 0.05 mol of H + correct 2. 0.05 mol of OH - and 0.015 mol of H + 3. 0.3 mol of OH - and 0.5 mol of H + 4. 0.5 mol of OH - and 0.3 mol of H + 5. 0.15 mol of OH - and 0.5 mol of H + Explanation: Buffer Stress 24:04, general, multiple choice, > 1 min, fixed.
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