## Chemistry 12th Edition

Published by McGraw-Hill Education

# Chapter 15 - Acids and Bases - Questions & Problems - Page 712: 15.78

#### Answer

(a) Neutral: pH = 7 (b) Basic: pH > 7 (c) Acidic: pH < 7 (d) Acidic: pH < 7

#### Work Step by Step

1. Identify if each ion is a strong or weak acid or base, or if it does not hydrolyze. (a) $Na^+$ does not hydrolyze (Conjugate acid from strong base: NaOH) $Br^-$ does not hydrolyze (Conjugate base from strong acid: HBr) (b) $K^+$ does not hydrolyze (Conjugate acid from strong base: KOH) $SO{_3}^{2-}$ hydrolyzes to produce $OH^-$ (Conjugate base from weak acid: $HSO{_3}^-$) (c) $NH{_4}^{+}$ hydrolyzes to produce $H^+$ (Conjugate acid from weak base: $NH_3$) $N{O_2}^-$ hydrolyzes to produce $OH^-$ (Conjugate base from weak acid: $HNO_2$) (d) $Cr^{3+}$ hydrolyzes to produce $H^+$ (Small metal ion with high charge) $NO_3^-$ does not hydrolyze (Conjugate base from strong acid: $HNO_3$) 2. If neither the anion nor the cation hydrolyze, the pH of the aqueous solution will be neutral (7). If the solution will produce only $H^+$, the aqueous solution will be acidic: pH < 7. If the solution only produces $OH^-$, the aqueous solution will be basic: pH > 7. If the solution produces both, we have to compare the strength of the electrolytes. (a) Neutral: pH = 7 (b) Basic: pH > 7 (c) According to tables 15.3 and 15.4: $NO_2^-$ has a Kb of $2.2 \times 10^{-11}$, and $NH_4^+$ has Ka = $5.6 \times 10^{-10}$ Therefore, $NH_4^+$, the acid, is stronger. The solution will be acidic: pH < 7 (d) Acidic: pH < 7

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