Chemistry: The Molecular Nature of Matter and Change 7th Edition

Published by McGraw-Hill Education
ISBN 10: 007351117X
ISBN 13: 978-0-07351-117-7

Chapter 19 - Problems: 19.14

Answer

pH of buffer = 3.27 Hydronium ion concentration = 5.4 x 10^-4 M

Work Step by Step

1 (A) Given : 1. [conjugate base] = [F-] = 0.25 M 2. [acid] = [HF] = 0.20 M 3. Ka of HF = 6.8 x 10^-4 2 (B) Formulae : 1. Henderson - Hasselbalch equation of a buffer : pH = pKa + log [conjugate base] / [acid] 2. pKa = -log Ka 3. pH = -log [H+] 3 (C) Solution : 1. pKa = -log Ka = - log (6.8 x 10^-4) = 3.17 .... (1) 2. pH = pKa + log [conjugate base] / [acid] = 3.17 + log (0.25 / 0.20) = 3.17 + 0.10 = 3.27 Hence, pH of the buffer is 3.7 3. pH of the solution = -log [H+] So, [H+] = 10^(-pH) = 10^(-3.27) = 5.4 x 10^-4 M 4 (D) Answer : pH of buffer = 3.27 Hydronium ion concentration = 5.4 x 10^-4 M
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