Acid salt

For example, in preparing sodium sulphate (Na2SO4) a certain amount of sodium hydroxide (NaOH) is needed to neutralize the sulphuric acid (H2SO4) to produce this salt. When preparing sodium hydrogen sulfate (NaHSO4, an acid salt), half of the required amount of sodium hydroxide for neutralization is used.

Such compounds can act as an acid or a base: Addition of an acid will restore protons, and addition of a base will consume protons. The actual pH of a solution of an acid salt will depend on the equilibrium constants involved, and whether the anion is a better proton donor or proton acceptor. A comparison between the Kb and Ka will indicate this: if Kb > Ka, the solution will be basic, whereas if Kb < Ka, the solution will be acidic.

Examples of acid salts include: sodium hydrogen sulfate (NaHSO4), sodium hydrogen carbonate[bisulphate bicarbonate] as well (NaHCO3), sodium hydrogen sulphide (NaHS), and phosphatase (a class of enzymes).

Common low-temperature acid salts include cream of tartar or, calcium phosphate, and citrate. High-temperature acid salts are usually aluminium salts, such as calcium aluminum phosphate. They can be found in many baking powders, also in many non-dairy coffee creamers.

Sal ácido 酸式盐