Answer
$CH_3NH_2(aq) + H_2O(l) \lt -- \gt CH_3N{H_3}^+(aq) + OH^-(aq)$
$K_b = \frac{[OH^-][CH_3N{H_3}^+]}{[CH_3NH_2]}$
Work Step by Step
1. Write the ionization chemical equation:
- Write the reaction where $CH_3NH_2$ takes a proton from a water molecule:
$CH_3NH_2(aq) + H_2O(l) \lt -- \gt CH_3N{H_3}^+(aq) + OH^-(aq)$
2. Now, write the $K_b$ expression:
- The $K_b$ expression is the concentrations of the products divided by the concentration of the reactants:
$K_b = \frac{[Products]}{[Reactants]}$
$K_b = \frac{[OH^-][CH_3N{H_3}^+]}{[CH_3NH_2]}$
*** We don't consider the $[H_2O]$, because it is the solvent of the solution.
