Editing Ammonium (section)

== Acid–base properties ==
[[File:Hydrochloric acid ammonia.jpg|thumb|Fumes from [[hydrochloric acid]] and ammonia forming a white cloud of [[ammonium chloride]]]]

The ammonium ion is generated when ammonia, a weak base, reacts with [[Brønsted–Lowry acid–base theory|Brønsted acids]] ([[proton]] donors):
: {{chem2|H+ + NH3 → [NH4]+}}
The ammonium ion is mildly acidic, reacting with Brønsted bases to return to the uncharged ammonia molecule:
: {{chem2|[NH4]+ + B- → HB + NH3}}
Thus, the treatment of concentrated solutions of ammonium salts with a strong base gives ammonia. When ammonia is dissolved in water, a tiny amount of it converts to ammonium ions:
: {{chem2|H2O + NH3 ⇌ OH- + [NH4]+}}

The degree to which ammonia forms the ammonium ion depends on the [[pH]] of the solution. If the pH is low, the equilibrium shifts to the right: more ammonia molecules are converted into ammonium ions. If the pH is high (the concentration of [[hydrogen ion]]s is low and [[hydroxide ion]]s is high), the equilibrium shifts to the left: the [[hydroxide]] ion abstracts a proton from the ammonium ion, generating ammonia.

Formation of ammonium compounds can also occur in the [[vapor]] phase; for example, when ammonia vapor comes in contact with hydrogen chloride vapor, a white cloud of ammonium chloride forms, which eventually settles out as a [[solid]] in a thin white layer on surfaces.