Question

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

$\mathbf{\text{Cl}}{{\mathbf{\text{O}}}_{\mathbf{2}}}^{-},{\mathbf{H}}_{\mathbf{2}}\mathbf{O},{\mathbf{NH}}_{\mathbf{3}},\mathbf{Cl}{{\mathbf{O}}_{\mathbf{4}}}^{-}$

Short answer

The stronger an acid (higher K_a value), the weaker is the conjugate base.

The order from strongest to weakest of the acids is:

${\text{HClO}}_4,H_3{O}^{+},HCl{O}_2,N{H_4}^{+},$

The order of basicity (strongest to the weakest base) is:

${\text{NH}}_3, Cl{O_2}^{-}, H_{2}O, Cl{O_4}^{-}$

Step-by-step solution

Basic Strength relation with Ka Value

Acid dissociation constant, i.e., K_atells us about the strength of an acid in solution. The higher the value of K_a, the stronger the acid is. The lower K_a value represents a weak acid. The weaker the acid, the stronger will be the conjugate base.

Relative Strength of given Bases

According to table 7.2:

$$\begin{gathered} \text{AcidFormulaNameK\_avalue} \\ \text{HClO\_2Chlorousacid1.0times10^-2} \\ \text{NH\_4^+Ammoniumion5.6times10^-10} \end{gathered}$$

${\text{HClO}}_4$has a very large value of K_a, so it’s a very strong acid, and K_a for${\text{H}}_3{O}^{+}$ is lesser than${\text{HClO}}_4$ .

So, the order from strongest to weakest is:

${\text{HClO}}_4,H_3{O}^{+},HCl{O}_2,N{H_4}^{+}$

The conjugate base of a strong acid will be weak, so the order (strongest to the weakest base) is

${\text{NH}}_3,Cl{O_2}^{-},H_{2}O,Cl{O_4}^{-}$