Normalidade

Normality (N): equivalents per liter

Normality states concentration as equivalents per liter of solution: N = M · z. M is the molarity and z is the equivalence factor, which counts how many H⁺ an acid donates, how many OH⁻ a base donates, or how many electrons change hands in a redox reaction. Take H₂SO₄ at 1 M: it comes out to 2 N, since each molecule releases 2 H⁺ (it's diprotic). NaOH 1 M, being monobasic, is just 1 N. Modern IUPAC steers people toward molarity instead, yet normality still earns its keep in classical analytical work, where the stoichiometry collapses to N_a · V_a = N_b · V_b.

Applications

It shows up in acid-base titration when you need the neutral point precisely, in redox titration such as permanganometry and iodometry, and in clinical chemistry, where electrolytes like sodium, potassium and calcium in blood plasma are reported in mEq/L. Classical water analysis for total hardness uses it too, as do qualitative analytical chemistry textbooks.

FAQ

Normality vs molarity? When z = 1, as with HCl or NaOH, the two numbers match. With H₂SO₄, H₃PO₄ or Ca(OH)₂ they split apart, and N always lands at or above M.

Why is normality discouraged? Because z hangs on the reaction itself. The same compound can carry different N values depending on the context, which leaves room for ambiguity.

What is mEq/L? Milliequivalents per liter, or N · 1000. It's the unit clinical laboratories reach for when reporting electrolytes.