Write an equation for the reaction of each of the following with water:
a. HF (a weak acid)
b. \mathrm{NH}_{3} (a weak base)
a. \mathrm{HF}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \rightleftarrows \mathrm{H}_{3} \mathrm{O}^{+}(a q)+\mathrm{F}^{-}(a q)
b. \mathrm{NH}_{3}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \rightleftarrows \mathrm{NH}_{4}^{+}(a q)+\mathrm{OH}^{-}(a q)