The problem stems from the scientists' mistaken belief that
ammonia dissociates easily into water to form ammonium hydroxide
(NH4OH), considering that it seemed to
dissolve readily into water.
They only realised later on that the degree of dissociation is
actually miniscule and that the reason why ammonia dissolves
readily in water is because of the strong hydrogen bonds formed
between the ammonia and water molecules. So it would actually be
more correct to say that aqueous ammonia solution has a formula of
NH3.H2O.
Anyway, I got confused as well... in my time, quite a few
references still referred to aqueous ammonia as 'ammonium
hydroxide' and used the old erroneous chemical formula.
