solution_pdf - elizondo(jie268 Homework 8 fakhreddine(51550...

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elizondo (jie268) – Homework 8 – fakhreddine – (51550) 1 This print-out should have 16 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 1.0points Some solid NH 4 Cl is added to a water solution of NH 3 . Which of the following statements is correct? 1. pH of the solution decreases. correct 2. [OH - ] of the solution increases. 3. pH of the solution increases. 4. [H 3 O + ] of the solution remains the same. Explanation: 002 1.0points Some solid KClO 2 is added to a water solution of HClO 2 . Which of the following statements is correct? 1. pH of the solution decreases. 2. [H 3 O + ] will remain the same. 3. pH of the solution increases. correct 4. [OH - ] of the solution decreases. Explanation: 003 1.0points What is the pH of a solution which is 0.600 M in dimethylamine ((CH 3 ) 2 NH) and 0.400 M in dimethylamine hydrochloride ( (CH 3 ) 2 NH + 2 Cl - ) ? K b for dimethylamine = 7 . 4 × 10 - 4 . 1. 10.87 2. 11.05 correct 3. 2.95 4. 11.21 5. 10.69 6. 3.31 7. 10.78 Explanation: K w = 1 × 10 - 14 K a = 0 . 00074 [(CH 3 ) 2 NH] = 0.6 M [(CH 3 ) 2 NH + 2 ] = 0.4 M K a , (CH 3 ) 2 NH + 2 = K w K b , (CH 3 ) 2 NH Applying the Henderson-Hasselbalch equa- tion, pH = p K a + log parenleftbigg [(CH 3 ) 2 NH] [(CH 3 ) 2 NH + 2 ] parenrightbigg = - log parenleftbigg K w K a parenrightbigg + log parenleftbigg [(CH 3 ) 2 NH] [(CH 3 ) 2 NH + 2 ] parenrightbigg = - log parenleftbigg 1 × 10 - 14 0 . 00074 parenrightbigg + log parenleftbigg 0 . 6 0 . 4 parenrightbigg = 11 . 0453 004 1.0points What is the approximate pH of a solution in which the concentration of benzoic acid is 1.0 M and the concentration of sodium benzoate is 0.10 M? 1. 6.64 2. 1.65 3. 5.20 4. 3.20 correct 5. 2.64 Explanation: bracketleftbig C 6 H 5 COO - bracketrightbig = 1 . 0 M [C 6 H 5 COOH] = 0 . 1 M pH = p K a + log parenleftBigg bracketleftbig C 6 H 5 COO - bracketrightbig [C 6 H 5 COOH] parenrightBigg = - log ( 6 . 3 × 10 - 5 ) + log 0 . 10 1 . 0 = 3 . 20066
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elizondo (jie268) – Homework 8 – fakhreddine – (51550) 2 005 1.0points Which solution is most basic? 1. 0.10 M HClO and 0.10 M NaClO 2. 0.10 M CH 3 COOH and 0.20 M NaCH 3 COO 3. 0.10 M CH 3 COOH and 0.10 M NaCH 3 COO 4. 0.10 M aq NH 3 and 0.10 M NH 4 Cl cor- rect 5. 0.10 M aq NH 3 and 0.20 M NH 4 Cl Explanation: All are buffers where pH = p K a + log parenleftbigg [base] [acid] parenrightbigg 006 1.0points Explain why the salt of a weak acid, as well as the acid itself, must be present to form a buffer solution.
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  • Spring '13
  • fakhreddine
  • pH, NH3, NH+

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