Aquaculture Technician Industry Certification Practice Test

In water, ammonia exists in two forms: the uncharged molecule NH3 and the ionized form NH4+. Ammonia acts as a weak base and accepts a proton from water, forming ammonium and hydroxide: NH3 + H2O ⇌ NH4+ + OH−. Because of this equilibrium, the ionized form NH4+ is the predominant species at typical environmental pH levels, while NH3 is more prevalent only at higher pH.

The other ions shown, NO2− and NO3−, are nitrite and nitrate—different nitrogen species altogether and not related to the ionization of ammonia. So the ionized form of ammonia in water is NH4+.