Question

Use Table 7.2 to order the following from the strongest to the weakest acid.

${\mathbf{HClO}}_{\mathbf{2}}\mathbf{}\mathbf{,}\mathbf{}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{}\mathbf{,}\mathbf{}{{\mathbf{NH}}_{\mathbf{4}}}^{\mathbf{+}}\mathbf{,}\mathbf{}{\mathbf{HClO}}_{\mathbf{4}}$

Short answer

K_a represents the acidic strength of the acid; the higher the value of K_a stronger the acid will be.

The order from strongest to weakest is:

${\mathrm{HClO}}_4,{\mathrm{HClO}}_2,{{\mathrm{NH}}_4}^{+},{\mathrm{H}}_2\mathrm{O}$

Step-by-step solution

Acidic Strength relation with Ka Value

Acid dissociation constant, i.e., K_a is a measure of the strength of an acid in solution. Higher the value of K_a means higher the dissociation of acid, which means the acid is stronger. The lower K_a value represents a weak acid.

Relative Strength of given acids

According to the table 7.2:

$$\begin{gathered} \mathrm{Acid}\mathrm{Formula}\mathrm{Name}{\mathrm{K}}_{\mathrm{a}}\mathrm{value} \\ {\mathrm{HClO}}_2\mathrm{Chlorous}\mathrm{acid}1.0\times {10}^{-2} \\ {{\mathrm{NH}}_4}^{+}\mathrm{Ammonium}\mathrm{ion}5.6\times {10}^{-10} \end{gathered}$$

${\mathrm{HClO}}_4$ has a very large value of K_a, so it’s a very strong acid, and K_a for water is $1.8\times {10}^{-16}$.

So, order from strongest to weakest is:

${\mathrm{HClO}}_4,{\mathrm{HClO}}_2,{{\mathrm{NH}}_4}^{+},{\mathrm{H}}_2\mathrm{O}$