What is the difference between ammonium and ammonia?

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t-nez eNotes educator| Certified Educator

Ammonia and ammonium differ by one hydrogen ion (H+). Ammonia is the common name for the compound nitrogen trihydride, which has the formula `NH_3` . Ammonium is the name of the ion `NH_4^+` . An ion is an atom or molecule that has a net charge. 

Ammonia is a base, meaning it produces `OH^- ` in solution. When ammonia reacts with water, an H+ ion is transferred from water to ammonia, forming ammonium ion, according to this equation:

`NH_3 + H_2O -> NH_4^+ + OH^-` 

Ammonia and ammonium ion are a conjugate acid-base pair. Ammonium ion is the conjugate acid of ammonia because it forms when when the base ammonia `(NH_3)` accepts a proton (H+ ion), as seen in the equation above. When the `NH_4^+` ion donates a proton, its conjugate base `NH_3` is formed. This occurs in the reverse reaction:

`NH_4^+ + OH^(-) -> NH_3 + H_2O`

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