The strength of a base is determined by its ability to donate hydroxide ions (OH-) in water. The more hydroxide ions a base can donate, the stronger it is.

- NaOH is a strong base because it completely dissociates in water, releasing all of its hydroxide ions.

$$NaOH_{(aq)} \rightarrow Na_{(aq)}^++ OH^-_{(aq)}$$

- NH3 is a weak base because only a small portion of it dissociates in water, releasing hydroxide ions.

$$NH_{3(aq)}+H_2O}_{(l)} \rightleftharpoons NH^+_{4(aq)}+ OH^-_{(aq)}$$

The equilibrium constant for the dissociation of NH3 in water is very small, which means that very few NH3 molecules actually dissociate. As a result, NH3 is a much weaker base than NaOH.