Acid-base equilibria
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I would like to know why ammonium salts behave as acids in liquid ammonia. I know that the Bronsted-Lowry theory of acid-base behaviour can be applied to solutions in liquid ammonia, but I am confused about the behaviour of ammonium salts in liquid ammonia. Is it connected with the fact that pure liquid ammonia ionises as follows:
NH3(l) + NH3(l) <=> NH4+(am) + NH2+ (am)?
Ulex replies
You have effectively answered your own question! You are quite correct. The ion NH4+ is the equivalent of H3O+ and NH2- is the equivalent of OH-.
In fact there are quite a few parallels between water and ammonia. They are, for example, isoelectronic (have the same total number of electrons). They both have lone pairs of electrons which are capable of accepting protons and can both form complexes with transition metal ions.
A solution of hydrochloric acid could be thought of as being H3O+Cl- just as ammonium chloride is NH4+Cl-.
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updated: 28 January 2005
