Acid: definition in chemistry
Acid: A substance that donates hydrogen ions (H⁺) to other substances. In water, acids raise the concentration of H⁺ ions and give a pH below 7.
Strong acids such as hydrochloric acid ionize almost completely in water, while weak acids such as acetic acid ionize only partly. Acids turn blue litmus red, react with many metals to release hydrogen gas and react with carbonates to release carbon dioxide. A broader definition, the Lewis theory, describes an acid as any substance that accepts a pair of electrons.
Examples
- Hydrochloric acid (HCl) — found in stomach acid
- Acetic acid (CH₃COOH) — gives vinegar its sour taste
- Citric acid — in lemons and limes
- Sulfuric acid (H₂SO₄) — used in car batteries
On the periodic table
Oxides of nonmetals on the right of the table, such as CO₂, SO₃ and P₄O₁₀, react with water to form acids.