Question

Is `"NH"_4^(+)` an acid or a base?

Answer 1

More often than not, an acid. It donates a proton by accepting two electrons. For instance:

`"NH"_4^(+)(aq) + "H"_2"O"(l) rightleftharpoons "NH"_3(aq) + "H"_3"O"^(+)(aq)`

Here:

Ammonium is the acid, donating the proton to water (Bronsted-Lowry definition) by accepting two electrons (Lewis definition) from water's oxygen.

Water is the base, donating two electrons (Lewis definition) from oxygen to accept one proton (Bronsted-Lowry definition) from ammonium.