NH3 is not a strong base. A weak base is defined as a base that does not completely dissociate into ions when in a solution. Weak bases are also known as weak electrolytes and reactions with them are reversible.
Weak bases only react with water in a small amount when in a solution. When reacting with water, the weak base accepts H+ ions. However, the majority of the solution in a state of equilibrium consists of the unionized form of the base, with about 10 percent consisting of the hydroxide ions and the conjugate acid.
In contrast, a strong base, such as an alkali metal, will completely break down into ions when placed in a solution.