General Chemistry: Principles and Modern Applications (10th Edition)

Published by Pearson Prentice Hal
ISBN 10: 0132064529
ISBN 13: 978-0-13206-452-1

Chapter 16 - Acids and Bases - Example 16-11 - Making Qualitative Predictions about Hydrolysis Reactions - Page 725: Practice Example B


$$H_2{PO_4}^-(aq) + H_2O(l) \leftrightharpoons HP{O_4}^{2-}(aq) + H_3O^+(aq) (1)$$ $$H_2{PO_4}^-(aq) + H_2O(l) \leftrightharpoons H_3P{O_4}(aq) + OH^-(aq) (2)$$ The acid reaction (1) occurs in a greater extent.

Work Step by Step

$H_2P{O_4}^-$ can act as an acid, forming $H{PO_4}^{2-}$ or as a base, forming $H_3PO_4$. 1. Write the reaction where it donates a proton (acid): $$H_2{PO_4}^-(aq) + H_2O(l) \leftrightharpoons HP{O_4}^{2-}(aq) + H_3O^+(aq)$$ 2. Write the reaction where it receives a proton (base): $$H_2{PO_4}^-(aq) + H_2O(l) \leftrightharpoons H_3P{O_4}(aq) + OH^-(aq)$$ 3. Since pH = 4.7, which is less than 7, the compound forms an acidic solution. Therefore, the acid reaction occurs in larger quantities than the basic reaction. $K_a \gt K_b$
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