Definition of Hydrolysis

Hydrolysis is the reaction of a substance with water. Some hydrolysis reactions involve reaction with H+ or OH- ions.
One common kind of hydrolysis involves reaction of the anion of a weak acid with water to form nonionized acid molecules and OH- ions. This upsets the H+/OH- balance in water and produces basic solutions.
In Brønsted–Lowry terminology anions of strong acids are extremely weak bases, whereas anions of weak acids are stronger bases. To refresh your memory, consider the following examples.
Nitric acid, a common strong acid, is essentially completely ionized in dilute aqueous solution. Dilute aqueous solutions of HNO3 contain equal concentrations of H+ and NO3- ions. In dilute aqueous solution nitrate ions show almost no tendency to react with H+ ions to form nonionized HNO3; thus, NO3- is a very weak base.

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HNO3 + H2O  H+ + NO3-
On the other hand, acetic acid (a weak acid) is only slightly ionized in dilute aqueous solution. Acetate ions have a strong tendency to react with H+ to form CH3COOH molecules. Acetic acid ionizes only slightly.
CH3COOH + H2O  H+ + CH3COO-
Hence, the CH3COO- ion is a stronger base than the NO3- ion, but it is still weak.
In the following sections we consider dilute aqueous solutions of salts. Based on our classification of acids and bases, we can identify four different kinds of salts.
1. Salts of strong bases and strong acids
2. Salts of strong bases and weak acids
3. Salts of weak bases and strong acids
4. Salts of weak bases and weak acids