Chapter 16, Problem 16.1P

Interpretation Introduction

Interpretation:

The balanced net ionic equations for the neutralization of equal molar amounts of the given acids and bases has to be determined. After neutralization, it is to be determine whether the pH in each combination of the given acid and base is greater than, or equal to or, less than 7.

Concept Introduction:

Any strong electrolyte can dissociate completely into its ions but for weak electrolyte only certain number of ions is dissociated. Hence, pH depends on the dissociated ions.

Answer to Problem 16.1P

Solution:

(a) $HN{O}_2(aq)+O{H}^{-}(aq)\rightleftarrows N{O}_2{}^{-}(aq)+H_{2}O(l)$ , pH >7

(b) $H^{+}(aq)+N{H}_3(aq)\rightleftarrows N{H}_4{}^{+}(aq)$ , pH<7

(c) $O{H}^{-}(aq)+H^{+}(aq)\rightleftarrows H_{2}O(l)$ , pH=7

Explanation of Solution

(a) $HN{O}_2$and $KOH$

Balanced Molecular equation:

$HN{O}_2(aq)+KOH(aq)\rightleftarrows KN{O}_2(aq)+H_{2}O(l)$

Total ionic equation:

$HN{O}_2(aq)+K^{+}(aq)+O{H}^{-}(aq)\rightleftarrows K^{+}(aq)+N{O}_2{}^{-}(aq)+H_{2}O(l)$

Net ionic equation:

$HN{O}_2(aq)+O{H}^{-}(aq)\rightleftarrows N{O}_2{}^{-}(aq)+H_{2}O(l)$

$HN{O}_2$ is a weak acid and $KOH$ is a strong base. So at equivalence point pH is greater than 7.

(b) $HBr$and $N{H}_3$

Balanced Molecular equation:

$HBr(aq)+N{H}_3(aq)\rightleftarrows N{H}_{4}Br(aq)$

Total ionic equation:

$H^{+}(aq)+B{r}^{-}(aq)+N{H}_3(aq)\rightleftarrows N{H}_4{}^{+}(aq)+B{r}^{-}(aq)$

Net ionic equation:

$H^{+}(aq)+N{H}_3(aq)\rightleftarrows N{H}_4{}^{+}(aq)$

$HBr$ is a strong acid and $N{H}_3$ is a weak base. So, at equivalence point pH is less than 7.

(c) $KOH$and $HCl{O}_4$

Balanced Molecular equation:

$HCl{O}_4(aq)+KOH(aq)\rightleftarrows KCl{O}_4(aq)+H_{2}O(l)$

Total ionic equation:

$K^{+}(aq)+O{H}^{-}(aq)+H^{+}(aq)+Cl{O}_4{}^{-}(aq)\rightleftarrows K^{+}(aq)+Cl{O}_4{}^{-}(aq)+H_{2}O(l)$

Net ionic equation:

$O{H}^{-}(aq)+H^{+}(aq)\rightleftarrows H_{2}O(l)$

$HCl{O}_4$ is a strong acid and $KOH$ is a strong base. So, at equivalence point pH is equal to 7.