Normality measures concentration in reactive equivalents per litre rather than moles per litre. The point is that some molecules pack more punch: one sulfuric acid molecule donates two protons, so a 1 M acid is "twice as reactive" — 2 N. The bridge is the n-factor, the number of reactive units (H⁺, OH⁻ or transferred electrons) per molecule, giving the simple rule N = M × n. It is the natural unit for titrations, where equivalents react one-for-one and the endpoint is just N₁V₁ = N₂V₂.
Reviewed: June 19, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: equivalent-concentration definitions.
The normality equations
The n-factor is the heart of it: 1 for monoprotic acids and bases (HCl, NaOH), 2 for diprotic species (H₂SO₄, Ca(OH)₂), 3 for triprotic H₃PO₄, and the number of electrons transferred for redox reagents. Equivalent weight is just the molar mass shared out among those equivalents. Both routes give the same answer — molarity times n, or mass per equivalent weight per litre — so use whichever data you have.
Worked example — standardising sulfuric acid
Scenario: A 0.5 M sulfuric acid solution; H₂SO₄ donates 2 H⁺, so n = 2 (molar mass 98 g/mol).
The acid is 1.0 N — twice its molarity, because each molecule supplies two protons. Both methods agree: 0.5 M × 2, or 4.9 g of acid (one-tenth of an equivalent weight per 100 mL) gives 1.0 N. In a titration this 1.0 N acid would neutralise a 1.0 N base in equal volumes, since equivalents always react 1:1 — the convenience that keeps normality in use for analytical work.
Frequently Asked Questions
N = M × n (n-factor). 0.5 M H₂SO₄ (n=2) = 1.0 N. Or N = mass/(equiv. weight × V_L).
Molarity = mol/L; normality = equivalents/L. Equal when n=1 (HCl, NaOH); differ otherwise. N = M × n.
Reactive units per molecule: H⁺ for acids, OH⁻ for bases, electrons for redox. HCl 1, H₂SO₄ 2, H₃PO₄ 3.
molar mass ÷ n. H₂SO₄: 98/2 = 49 g/equivalent. Mass ÷ eq. weight = equivalents.
Acid–base and redox titrations: equivalents react 1:1, so N₁V₁ = N₂V₂. IUPAC discourages it elsewhere.