Acid
A substance that donates protons, produces hydrogen ions in water, or accepts a pair of electrons.
Formula / equation
HA → H⁺ + A⁻
Unit
Dimensionless
In depth
Acids taste sour, turn litmus red, conduct electricity in solution and react with metals, carbonates and bases. Their strength depends on how readily the proton is released, which is governed by the stability of the resulting anion and the polarity and strength of the bond to hydrogen.
Examples in the real world
Hydrochloric acid in the stomach, citric acid in lemons, and sulfuric acid in a car battery.