Pharmaceutical Chemistry

Normality Calculator

Calculates the normality of a solution, or how much solid or liquid reagent you need for a target normality.

Normality

0.0274N (eq/L)

Moderately dilute solution

Reagent

Pick a common reagent, or enter its equivalent weight yourself.

Quick chemical selection

Gram equivalent weight (Eq.W)

g/eq

MW divided by n-factor. HCl 36.46, NaOH 40.00, H₂SO₄ 49.04.

Inputs

Amount of solid

Mass weighed out and dissolved.

Final volume of solution (V)

Volume after making up in a volumetric flask.

Working

The numbers you entered, plugged into the formula.

Equivalent weight36.46g/eq

Final volume1 L = 1.0000L

N = (1 g = 1.0000 g) / (36.46 × 1.0000) = 0.0274

For solids:

N = (mass in g) / (Eq.W × volume in L)

For liquids:

N = (A × sg × purity%) / (Eq.W × V)

Required mass (g) = N × Eq.W × V · Required volume (mL) = (N × Eq.W × V) / (sg × purity%)

N — normality (eq/L). Eq.W — equivalent weight = MW / n. mass — mass of solid, converted to grams. A — amount of liquid (mL). sg — specific gravity (g/mL). purity% — percentage purity, used as a decimal. V — final volume, converted to litres.

For a liquid, A × sg gives the mass of liquid taken, and × purity leaves only the mass of the pure substance. Dividing mass by Eq.W gives equivalents; dividing by litres gives normality.

References

Beckett AH, Stenlake JB. Practical Pharmaceutical Chemistry, Part 1. 4th ed. London: Athlone Press; 1988.

Common questions

Molarity counts moles per litre; normality counts equivalents per litre. N = M × n-factor, so 1 M H₂SO₄ (n = 2) is 2 N, while 1 M HCl (n = 1) is 1 N.

For acids it is the number of replaceable H⁺, for bases the number of OH⁻, for salts the total cation charge, and for oxidising or reducing agents the electrons gained or lost per molecule in that reaction.

Concentrated reagents are measured by volume but are not pure. Volume × specific gravity gives the mass of liquid, and purity tells you how much of that mass is the actual acid or base.

Normalities below 0.001 N are shown as, for example, 2.743e-8 — that means 2.743 × 10⁻⁸ N. Check the mass unit if you did not expect such a dilute solution.

About normality

Normality (N) is the number of gram equivalents of a substance per litre of solution. One equivalent is the amount that supplies or reacts with one mole of H⁺, OH⁻ or electrons, so normality counts reacting capacity rather than molecules.

Use it when

Preparing standard acid, base or redox solutions for titration

Converting between the mass of a solid and the normality it gives

Diluting a concentrated liquid reagent (e.g. conc. H₂SO₄ or HCl) to a set normality

n-factor guidelines

AcidsNumber of H⁺ ions

HCl:1, H₂SO₄:2, H₃PO₄:3

BasesNumber of OH⁻ ions

NaOH:1, Ca(OH)₂:2

SaltsTotal charge

Na₂CO₃:2, KMnO₄:5

Redox AgentsElectrons transferred

KMnO₄:5, K₂Cr₂O₇:6

Read with care

The n-factor depends on the reaction: KMnO₄ is 5 in acid but 3 in neutral solution

For liquids, purity is the % w/w assay on the bottle label and sg its specific gravity

Always add concentrated acid to water, never water to acid

Prepared by the PharmaWallah student team. Verify results with your textbook or instructor. Report an error · Editorial policy