When ammonia (NH3) dissolves in water, it undergoes a chemical reaction known as ionization or dissociation. During this process, the ammonia molecule interacts with water molecules to produce two types of ions: ammonium ions (NH4+) and hydroxide ions (OH-).

The ionization of ammonia in water can be represented by the following chemical equation:

NH3 + H2O ⇌ NH4+ + OH-

In this reaction, an ammonia molecule (NH3) accepts a hydrogen ion (H+) from a water molecule (H2O), forming an ammonium ion (NH4+). Simultaneously, the water molecule that donates the hydrogen ion releases a hydroxide ion (OH-).

The equilibrium constant (Kb) for the ionization of ammonia in water at room temperature (25°C) is approximately 1.8 x 10-5. This indicates that the ionization of ammonia is a relatively weak process, meaning that the majority of the ammonia molecules remain un-ionized in solution.

The presence of ammonium and hydroxide ions in the solution contributes to the basic properties of aqueous ammonia. The hydroxide ions produced during ionization can react with other acids present in the solution, leading to an increase in the pH and a decrease in the acidity of the solution.