Chapter U6, Problem 15STP

Interpretation Introduction

Interpretation:

The correct equation for the dissociation of nitrous acid needs to be determined.

Concept introduction:

For an equilibrium reaction as follows:

$A+B\rightleftharpoons AB$

The expression for equilibrium constant is as follows:

$K=\frac{\left[AB\right]}{\left[A\right]\left[B\right]}$

Here, $\left[A\right],\left[B\right]\text{ and }\left[AB\right]$ is equilibrium concentration of A, B and AB.

Answer to Problem 15STP

Option (a)

Explanation of Solution

From the given table, it can be seen that the concentration of HNO₂ at the starting of reaction is 1.0 M and after the reaction it becomes 0.97 M. Also, the concentration of both H+ and NO₂- is 0.023 M. This indicates that HNO₂ does not completely dissociate into hydrogen ion and NO₂-ion. Thus, it is a weak acid.

For a weak acid, dissociation reaction is represented as follows:

$\text{HA}\rightleftharpoons {\text{H}}^{+}+{\text{A}}^{-}$

Thus, the dissociation reaction of HNO₂ will be:

${\text{HNO}}_{\text{2}}\left(aq\right)\rightleftharpoons {\text{H}}^{+}\left(aq\right)+{\text{NO}}_2{}^{-}\left(aq\right)$

Thus, correct option is (a).