Question

Which of the following represents the hydrolysis of the ammonium ion?

		NH3(aq) + H2O(l) ⇄ NH4+(aq) + OH-(aq)
		NH3(aq) + H3O+(aq) ⇄ NH4+(aq) + H2O(l)
		NH4+(aq) + OH-(aq) ⇄ NH3(aq) + H2O(l)
		NH4+(aq) + H2O(l) ⇄ NH3(aq) + H3O+(aq)

Answer 1

NH3(aq) + H2O(l) ⇄ NH4+(aq) + OH-(aq) ------------------ (1)

NH3(aq) + H3O+(aq) ⇄ NH4+(aq) + H2O(l) ----------------(2)

NH4+(aq) + OH-(aq) ⇄ NH3(aq) + H2O(l) ------------------ (3)

NH4+(aq) + H2O(l) ⇄ NH3(aq) + H3O+(aq) ----------------(4)

By definition hydrolysis is a simple chemical reaction where water is used to break down bonds of any substance into its ions. Specifically hydolysis means seprating the chemicals when they are added in water. There are three common types of hydolysis acid, base and salt hydrolysis.

The first reaction (reaction 1) is an example of base hydrolysis where ammonia acts as a base and accepts proton from from water to form NH4+ and OH- ions. So this not hydrolysis of ammonium ion, but a base. Therefore this does not represent the hydrolysis of ammonium ion.

The second reaction (reaction 2) NH3 again acts as a base and reacts with H3O+ to give NH4+ ion and water. Also here the solvent is not liquid water but an acidic solution (H3O+). Therefore it is also not hydolysis of ammonium ion.

In the third reaction (reaction 3) the NH4+ reacts as an ion with OH- to give NH3 and liquid water. Although NH4+ ion present here but the solvent is basic in nature. Infact liquid water being produced due to the reaction. Therefore this is also not hydrolysis of ammonium ion.

In the last reaction (reaction 4) NH4+ ion reacts with liquid water to produce aqueous ammonia and H3O+. This is an example of salt hydrolysis where salt (NH4+) of a weak base reacts with liquid water directly. This is most common type hydrolysis and hence represents the hydrolysis of ammonium ion.

Therefore the last reaction (reaction 4) represents the hydrolysis of the ammonium ion.