Ka and Kb refer to the acid and base dissociation constants of a compound. These indicate the extent to which an acid or a base dissociates. A strong acid has a large Ka value, and a strong base has a large Kb value.
The Kb of NH4OH is 1.790 x 10^-5.
For a base `[OH^-]= sqrt(Kb * C)`
As the given NH4OH solution has a concentration of 0.1938 mol/L and Kb = 1.790 x 10^-5
`[OH^-] = sqrt(1.790 * 10^-5 * 0.1938)`
`[OH^-] = 1.8625*10^-3`
`[H^+] = 5.369*10^-12`
The pH of a solution is the negative logarithm of the hydrogen ion concentration `[H^+]` . `pH = -log[H^+]` .
For the given solution, `pH = -log(5.369*10^-12)` = 11.27.
A 0.1938 mol/L NH3 solution, where Kb(NH4OH)=1.790x10^-5 is 11.27.