The ionisation constant of $\mathrm{N}{\mathrm{H}}_4^{+}$ in water is 5.6 $\times 10^{-10}$ at 25 $°\mathrm{C}$ . The rate constant for the reaction of $\mathrm{N}{\mathrm{H}}_4^{+}$ and $\mathrm{O}{\mathrm{H}}^{-}$ to form $\mathrm{N}{\mathrm{H}}_3$ and ${\mathrm{H}}_2\mathrm{O}$ at $25°\mathrm{C}$ is $3.4\times 10^{10}/\mathrm{m}\mathrm{o}{\mathrm{l}}^{-1}{\mathrm{S}}^{-1}$ . The rate constant for proton transfer from water to $\mathrm{N}{\mathrm{H}}_3$ is