Question

The pk of CH NH,+ equals 10.6; the pK_of (CH3)2NH,* equals 10.7. Which is the stronger base, CH NH, or (CH3)2NH²

Answer 1

Explanation:

Relation between $pK_{a}$ and $pK_{b}$ is as follows.

                          $pK_{a} + pK_{b}$ = 14

Hence, putting the given values of $pK_{a}$ in order to calculate the value of $pK_{b}$ as follows.

 For $CH_{3}NH^{+}_{3}$ : $pK_{a} + pK_{b}$ = 14

                       10.6 + $pK_{b}$ = 14

                           $pK_{b}$ = 14 - 10.6

                                         = 3.4

For $(CH_{3})_{2}NH^{+}_{2}$ : $pK_{a} + pK_{b}$ = 14

                           10.7 + $pK_{b}$ = 14

                           $pK_{b}$ = 14 - 10.7

                                         = 3.3

Hence, smaller is the value of $pK_{b}$ of a specie more will be the value of its $K_{b}$. Therefore, stronger will be the base.

Thus, we can conclude that $(CH_{3})_{2}NH^{+}_{2}$ will be the stronger base.