Why is ammonia not an arrhenius base?

An Arrhenius base must contain the hydroxide ion, because by definition, Arrhenius bases release OH- when dissolved in water. As a result, like lithium hydroxide, calcium hydroxide, and sodium hydroxide are all Arrhenius bases.

Ammonia, on the other hand, has the formula ##NH_3##. Because it doesn't contain the hydroxide ion, it cannot be an Arrhenius base. This is the very reason that the Bronsted-Lowry definition was devised, as it was known that ammonia behaved as a base in water.

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