BioDeviceHub

Normality Calculator

Convert between molarity and normality, or find the mass of solute for a normal solution, from the number of equivalents per mole in your reaction.

Formula

N=M×nN = M \times n
equivalent weight=MWn\text{equivalent weight} = \dfrac{\mathrm{MW}}{n}
m=N×V×MWnm = \dfrac{N \times V \times \mathrm{MW}}{n}
NN
normality, in equivalents per litre
MM
molarity, in mol/L
nn
equivalents supplied by one mole of the reagent in the reaction at hand
VV
final volume of the solution, in litres
mm
mass of solute, in grams

How it works

An equivalent is the amount of a reagent that supplies or consumes one mole of the reacting unit: one mole of H⁺ in an acid-base reaction, or one mole of electrons in a redox reaction. Normality is the number of equivalents per litre, so it equals the molarity multiplied by the equivalents each mole provides.

The number of equivalents belongs to the reaction, not to the compound. The same bottle of phosphoric acid is 1, 2 or 3 equivalents per mole depending on which end point it is titrated to. For that reason NIST describes normality as obsolete and recommends stating the amount concentration instead; it remains in wide use in titration procedures and pharmacopoeias, which is why it is supported here.

Worked example

Prepare 500 mL of 0.1 N sodium carbonate (Na₂CO₃, 105.99 g/mol) for a titration to the second end point, where each mole accepts two H⁺.

  1. Equivalent weight = 105.99 g/mol / 2 = 52.995 g per equivalent.
  2. m = 0.1 eq/L × 0.5 L × 52.995 g/eq = 2.64975 g.

Weigh 2.65 g of sodium carbonate and make the volume up to 500 mL. The same solution is 0.05 M.

These are the values the calculator opens with, so you can check its output against this example.

Assumptions

  • The reaction proceeds with the number of equivalents you enter.
  • The reagent is 100% pure and the molecular weight matches the form in the bottle.
  • The volume is that of the finished solution.

Common mistakes

  • Taking the equivalents from the formula without checking the reaction. Phosphoric acid titrated to its first end point supplies one H⁺, not three.
  • Using five equivalents per mole for permanganate outside acidic solution. The five-electron reduction to Mn²⁺ applies only in acid.
  • Mixing normal and molar concentrations in one calculation without converting.

Related tools

Molarity CalculatorMass, concentration or volume for a molar solutionOpen calculatorMolecular Weight CalculatorMolar mass and composition from a chemical formulaOpen calculatorBuffer Calculator (Henderson-Hasselbalch)Acid and base amounts for a buffer at a target pHOpen calculatorConcentration Unit ConverterMolar, mass per volume, mg/dL and % w/vOpen calculator