solution7_pdf - elizondo(jie268 Homework 7...

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elizondo (jie268) – Homework 7 – 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 What would be the pH of a 0.25 M solution of phenylamine (C 6 H 5 NH 2 ) at room temper- ature? The K b of phenylamine is 4 × 10 10 . 1. 5 2. 13 3. 9 correct 4. 1 5. 10.5 Explanation: [OH ] = (K b · C b ) 1 / 2 = (4 × 10 10 · 0 . 25) 1 / 2 = (10 10 ) 1 / 2 = 10 5 pOH = log[OH ] = log(10 5 ) = 5 pH = pK w pOH = 14 5 = 9 002(part1of2)1.0points The percentage protonation of octylamine (an organic base) in a 0 . 1 M aqueous solution is 6 . 7%. What is the pH of the solution? Correct answer: 11 . 8261. Explanation: M octylamine = 0 . 1 mol/L P = 6 . 7 100 = 0 . 067 octylamine octylamine H + + OH +H 2 O 0 . 1 0 0 x + x + x 0 . 1 x x x The equilibrium concentrations are x = [octylamine H + ] = [OH ] = P M octylamine = 0 . 067 (0 . 1) = 0 . 0067 and [octylamine] = 0 . 1 x = 0 . 1 0 . 0067 = 0 . 0933 . The pOH of the solution is pOH = log([OH ]) = log(0 . 0067) = 2 . 17393 and the pH is pH = 14 2 . 17393 = 11 . 8261 . 003(part2of2)1.0points What is the K b of octylamine? Correct answer: 0 . 000481136. Explanation: The K b is K b = [octylamine H + ][OH ] [octylamine] = (0 . 0067) 2 0 . 0933 = 0 . 000481136 . 004 1.0points Which of the following solutions has the low- est pH at 25 C? 1. 0.5 M formic acid correct 2. 0.5 M aniline 3. 0.1 M acetic acid 4. 0.1 M ammonia Explanation: 005 1.0points Calculate the equilibrium concentration of sulfurous acid in a solution labeled “0.100 M H 2 SO 3 (aq).” (p K a1 = 1 . 81, p K a2 = 6 . 91)
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elizondo (jie268) – Homework 7 – fakhreddine – (51550) 2 1. 0.015 M 2. 0.068 M correct 3. 0.050 M 4. 0.100 M 5. 0.032 M Explanation: 006 1.0points Calculate the molarity of C 2 O 2 4 in 0 . 22 M oxalic acid (H 2 C 2 O 4 ) if K a1 = 0 . 059, K a2 = 6 . 5 × 10 5 and K w = 1 × 10 14 . Correct answer: 6 . 5 × 10 5 mol / L.
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  • Spring '13
  • fakhreddine
  • pH, Weak acid

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