salt hydrolysis
/ hy-DROL-ih-sis /
You might expect that dissolving a salt — a product of an acid meeting a base — always gives plain neutral water. Yet dissolve baking soda and the water turns mildly basic; dissolve ammonium chloride and it turns slightly acidic. That surprise is salt hydrolysis: the salt's own ions quietly reacting with water.
When a salt dissolves, its ions separate, and some of them are the conjugate partners of weak acids or weak bases. Such an ion is not a passive bystander: it can pull a proton from water or donate one to it, generating a little extra hydroxide or hydronium. The ion of a weak acid makes the solution basic; the ion of a weak base makes it acidic; ions from strong acids and strong bases leave the water neutral.
Salt hydrolysis matters because it explains why so many real solutions are not at pH 7 even when no obvious acid or base was added — soil, blood, and processed foods all feel its touch. The key to predicting it is to remember which parent acid and base each ion came from: only the leftovers of weak parents are active enough to shift the pH.
Sodium acetate is the salt of a strong base and a weak acid. Dissolved in water, the acetate ions grab protons from water, releasing hydroxide, so the solution turns mildly basic.
Ions left over from a weak parent acid or base react with water and shift the pH.
A quick rule: salt of strong acid + strong base is neutral; strong base + weak acid is basic; strong acid + weak base is acidic; weak acid + weak base depends on which is weaker (compare their Ka and Kb).