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Unformatted text preview: Version 028 Exam 2 Holcombe (52460) 1 This printout should have 33 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. Some constants: Kw=1e14; R=8.314 J/K mol 001 10.0 points What is the concentration of SO 2 4 in 2.0 M H 2 SO 4 ? K a1 is strong and K a2 = 1 . 2 10 2 . 1. 4 . 10 1 M 2. 4 . 10 2 M 3. 1 . 2 10 2 M correct 4. 1 . 10 7 M 5. 2 . 10 1 M Explanation: 002 10.0 points You have a weak molecular base with K b = 6 . 6 10 9 . What is the pH of a 0.0500 M solution of this weak base? 1. pH = 9.26 correct 2. pH = 7.12 3. pH = 3.63 4. pH = 4.74 5. None of these Explanation: [base] = 0.05 M As mentioned, this is a weak base, so use the equation to calculate weak base [OH ] concentration: [OH ] = radicalbig K b C b = radicalBig (6 . 6 10 9 ) (0 . 05) = 1 . 81659 10 5 After finding [OH ], you can find pH using either method below: A) pOH = log ( 1 . 81659 10 5 ) = 4 . 74074 pH = 14 4 . 74074 = 9 . 25926 or B) K w = [H + ][OH ] = 1 10 14 [H + ] = K w [OH ] = 1 10 14 1 . 81659 10 5 = 5 . 50482 10 10 pH = log ( 5 . 50482 10 10 ) = 9 . 25926 003 10.0 points A diprotic acid H 2 A has values of K a1 = 1 . 10 6 and K a2 = 1 . 10 10 . What is the [A 2 ] in a 0.10 M solution of H 2 A? 1. 3 . 2 10 4 M 2. 3 . 2 10 6 M 3. 1 . 10 10 M correct 4. 0.10 M 5. 0.20 M Explanation: 004 10.0 points The pH of a solution changes from 5.5 to 3.5. This indicates that the [OH ] of the solution has 1. decreased by a factor of 2. 2. increased by a factor of 2. 3. decreased by 2 M. 4. increased by a factor of 100. 5. increased by 2 M. 6. decreased by a factor of 100. correct Explanation: Version 028 Exam 2 Holcombe (52460) 2 005 10.0 points What would be the pH of a 1 M solution of Na 2 HPO 4 ? Assume H 3 PO 4 has a p K a 1 of 2 and a p K a 2 of 7 and a p K a 3 of 13. 1. 13 2. 4.5 3. 7.5 4. 10 correct 5. 7 6. 2 Explanation: For a solution composed of a single ampho teric species (HPO 4 2 ), pH = 0 . 5(p K a 2 + p K a 3 ) = 0 . 5(7 + 13) = 10 006 10.0 points When dissolved in water, bases produce 1. hydronium ions. 2. salts. 3. OH ions. correct 4. H + ions. 5. H 3 O + ions. Explanation: Bases produce hydroxide ions (OH ) in wa ter; acids produce hydronium ions (H 3 O + ). 007 10.0 points What is the pH of a solution made by dissolving 0.100 mole of sodium acetate (NaCH 3 COO) in enough water to make one liter of solution? K a for CH 3 COOH is 1 . 80 10 5 . 1. 9.25 2. 5 . 56 10 10 3. 5 . 56 10 11 4. 8.87 correct 5. 1 . 82 10 6 6. 5.13 7. 10.25 8. 1 . 80 10 6 9. 3.75 10. 7 . 46 10 6 Explanation: 008 10.0 points Sodium fluoride is added to pure water and stirred to dissolve. Compared to pure water, the new solution is 1. neutral pH 2. More than one of these is true.More than one of these is true....
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 Spring '10
 McCord

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