Strength of acids or bases refers to their ability to donate and accept H ions respectively. When nitric acid is dissolved in water all or almost all of the H in the acid is released as H . None or almost none of the nitric acid molecules exist as such. When lactic acid is dissolved in water a considerable quantity remains as lactic acid molecules. Lactic acid is, therefore, said to be a weaker acid than nitric acid and the lactate ion a stronger base than nitrate ion.
Carbonic acid ionizes less than lactic acid and so is weaker than lactic acid.
Thus lactic acid might be referred to as weak when considered in relation to nitric acid but strong when compared to carbonic acid. Weak and strong in relation to acids and bases are thus relative terms. As we now measure pH rather than quantitate the levels of base in the blood, pH status would be a more appropriate term than acid-base status. Such a solution contains both acidic and basic groups. A mixture of a weak acid or a weak base and a salt of that acid or base in solution is a buffer solution.