# Chapter 15 - Aqueous Equilibria: Acids and Bases - Section Problems - Page 649: 47

(A) $H{CO_3}^-$ and (C) $H_2O$

#### Work Step by Step

(a) $HC{O_3}^-$ can act like an acid, and turn into $C{O_3}^{2-}$, or can act like a base, and turn into $H_2CO_3$ (b) $CN^-$ is a base, but it can't act like an acid. (c) $H_2O$ can act like an acid, and turn into $OH^-$, or can act like a base, and turn into $H_3O^+$. (d) $H_2CO_3$ is an acid, but it can't act like a stable base.

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