Acid salt

Chemical structure of sodium bicarbonate

Acid salts are a class of salts formed when a dibasic or tribasic acid has been neutralized to some degree. Because the acid is only partially neutralized, one or more replaceable protons remain. Typically this will lead to a formula with one or more metal ions, one or more protons, and an anion, such as sodium bicarbonate (NaHCO₃), sodium hydrosulfide (NaHS), sodium bisulfate (NaHSO₄), monosodium phosphate (NaH₂PO₄), and disodium phosphate (Na₂HPO₄).

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

Such compounds can act either 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 K_b and K_a will indicate this: if K_b > K_a, the solution will be basic, whereas if K_b < K_a, the solution will be acidic.

Use in food

Some acid salts are used in baking. They are found in baking powders and are typically divided into low-temperature (or single-acting) and high-temperature (or double-acting) acid salts. Common low-temperature acid salts react at room temperature to produce a leavening effect. They include cream of tartar, calcium phosphate, and citrates. High-temperature acid salts produce a leavening effect during baking and are usually aluminium salts such as calcium aluminium phosphate. Some acid salts may also be found in non-dairy coffee creamers.

See also

• alkali salt

References

This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (February 2008)