Normality

In chemistry, normality (N) is a term used to indicate chemical concentrations that is typically only used for acid-base reactions. A 1 normal (1 N) solution of any acid can neutralize an equal volume of any 1 N base solution. A one liter volume of a 1 N acid solution will neutralize one mole, or about 6.02⋅10²³ (Avogadro's number) hydroxide ions OH⁻. Normality is always greater than or equal to the related concentration unit molarity, such that

$\mathbf {N} =\mathbf {n} \times \mathbf {M}$

where n is an integer greater than or equal to 1. In acid-base reaction n is the number of protons (forming H₃O⁺) donated by one molecule of the acid. The molecular weight divided by n is the equivalent weight.

For a monoprotic acid like hydrochloric acid, HCl, which can provide only 1 mole of protons ( hydronium ions, H₃O⁺) per mole of acid, 1 M = 1 N. A diprotic acid like sulfuric acid, H₂SO₄, provides two moles of protons per mole of acid (n=2) and thus a 1 M solution of sulfuric acid is a 2 N solution.