This animation demonstrates the difference in ionization between a strong base, sodium hydroxide, and a weak base, ammonia. Click on one of the buttons to view sodium hydroxide (NaOH) or ammonia (NH3) dissolving in water.
Sodium hydroxide (NaOH) dissolved in water, is a strong base. Strong bases are strong electrolytes. For most purposes, strong bases ionize completely in water and produce a significant number of hydroxide ions. The Arrhenius definition of a base is a substance that ionizes in water to produce hydroxide ions. The Brønsted definition of a base is a substance that accepts protons or hydrogen ions (H+). Hydroxide is the strongest base that can exist in water. Hydroxide ions will readily accept H+ from an added acid to produce water. OH- + H+ --> H2O
Ammonia (NH3) dissolved in water, is a weak base. Weak bases are weak electrolytes, which only ionize to a limited extent in water. At equilibrium, an aqueous solution of ammonia contains mostly non-ionized ammonia molecules (NH3) and a small amount of ammonium ions (NH4+) and hydroxide ions (OH-). Given equal concentrations of an ammonia solution and a sodium hydroxide solution, the weak base (ammonia) will produce a much lower concentration of hydroxide ions than the strong base (sodium hydroxide).
Note that water molecules surrounding or hydrating each of the ions or molecules in solution were not shown in this animation. The main focus of this animation is to show the transfer of a hydrogen ion from water to ammonia.