Ammonium chloride Question

[Kyle461]

A bit of an embarrassment but I can't seem to wrap my head around this connection to saltwater tanks, even as a chemistry teacher. It's highly recommended in a fishless cycle to use solutions that are basically NH4Cl dissolved in water as an introductory solution of ammonia needed to start the cycle.

Here's my question. As far as I know when NH4Cl dissolves in water it breaks into its ions: NH4+ and Cl-. Where does ammonia (NH3) come from when using this as a way to introduce ammonia?

 

[Kyle461]

Nevermind.....I may have answered my own question. I forgot to consider partial ionization.

"For example, when ammonium chloride is dissolved in water, it gives an acidic solution because ammonium ion is a strong conjugate acid of the weak base ammonia, but chloride ion is a weak conjugate base of the strong acid hydrochloric acid.

NH 4 + ( aq ) + H 2 O ( l ) → NH 3 ( aq ) + H 3 O + ( aq )"

 

[shermanator]

The pKa is ~9.5, so ammonia in water will be ammonium ion (at least 10:1, depending your tank pH).