Chemistry and Chemical Reactivity (9th Edition)

Published by Cengage Learning
ISBN 10: 1133949649
ISBN 13: 978-1-13394-964-0

Chapter 16 Principles of Chemical Reactivity: The Chemistry of Acids and Bases - 16-8 Polyprotic Acids and Bases - Review & Check for Section 16-8 - Page 617: 1



Work Step by Step

Since Kb1 is much bigger than Kb2, we can simplify the problem by assuming that the dissociation of $N_2H_5^+$ and formation of $OH^-$ in the second reaction won't affect the first equilibrium. 1) $K_{b1}=[N_2H_5^+][OH^-]/[N_2H_4]$ $8.5\times10^{-7}=x\dot{}x/(0.025-x)$ $x=1.45\times10^{-4}\ M$ 2) $K_{b2}=[N_2H_6^{2+}][OH^-]/[N_2H_5^+]$ $8.9\times10^{-16}=y(1.45\times10^{-4}+y)/(1.45\times10^{-4}-y)$ $y\approx8.9\times10^{-16}\ M$ $[OH^-]\approx1.45\times10^{-4}\ M$ $pH=14+log([OH^-])=10.16$
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