Question #a20b5

1 Answer
Stefan V.
Nov 7, 2016

The solution is basic.

Explanation:

Take a look at the balanced chemical equation given to you

#"NH"_ (3(g)) + "H"_ 2"O"_ ((l)) rightleftharpoons "NH"_ (4(aq))^(+) + "OH"_ ((aq))^(-)#

Notice that the reaction produces hydroxide anions, #"OH"^(-)#, so right from the start you can say that the resulting solution will be basic, i.e. its pH will be #>7#.

It's true that the ammonium cation, #"NH"_4^(+)#, is a weak acid, but the small concentration produced by the ionization of ammonia and the very low concentration of ammonium cations that actually produce hydronium cations in solution allow you to completely ignore this species in the resulting solution.

So, the reaction produces hydroxide anions, which in turn decrease the concentration of hydronium cations and increase the pH of the solution.

Ammonia is considered a weak base because it does not ionize completely to produce hydroxide anions, i.e. the majority of the ammonia molecules dissolved in aqueous solution will not ionize.

http://academic.cuesta.edu/gbaxley/chem1a/notes/all_you_need_to_know_about_acids.htm

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