Ammonia is NH₃, or hydrogen nitride, so it would seem like it would be an acid. However, as we all know, it's a base. Why is this?

actually ammonia, like water, is amphiprotic, meaning it can act as a base OR an acid. It can even autoionize like water:

 

[ce]NH3 + NH3 -> NH2- + NH4+[/ce]

 

The NH2- ion isn't a common one, though, and the equilibrium constant for the reaction above is about 10^-30.

 

NH3 is much more likely to gain a proton (or give away its lone pair) than to lose a proton.

Ammonia dissolves in water to give ammonium hydroxide.

Thats the reason why it turns moist red litmus blue.

By Lowry Bronsted theory bases are proton acceptors.

ammonia accepts a proton from water(hydrogen ion).

Ammonia also accepts hydogen ions from acids and forms the respective ammonium salts.

 

Ammonia can also behave as a weak acid:

[ce]2Li + 2NH3 -> 2LiNH2 + H2[/ce]

Edited May 14, 201015 yr by Physicsfan

Ammonia dissolves in water to give ammonium hydroxide.

Thats the reason why it turns moist red litmus blue.

By Lowry Bronsted theory bases are proton acceptors.

ammonia accepts a proton from water(hydrogen ion).

Ammonia also accepts hydogen ions from acids and forms the respective ammonium salts.

 

Ammonia can also behave as a weak acid:

[ce]2Li + 2NH3 -> 2LiNH2 + H2[/ce]

 

ammonium hydroxide has never been isolated. it may form ammonium ions and hydroxide ions, but not ammonium hydroxide. we dont say that water forms hydronium hydroxide.

The number of [ce]H3O+[/ce] ions and the number of [ce]OH-[/ce] ions in pure water is equal, and so it is neutral. But in a solution of ammonia, the number of [ce]OH-[/ce] ions exceeds the number of [ce]H3O+[/ce] ions so it exhibits the properties of an alkali.