Why is ammonia a base?

[flarn2006]

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?

[hermanntrude]

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.

[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]

Edited May 14, 2010 by Physicsfan

[hermanntrude]

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.

[Physicsfan]

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.