How to use this calculator
- Choose what you want to do.
- Pick the chemical to fill molar mass, n-factor, purity and density, or enter your own.
- Enter the target normality and final volume (or the mass you used).
- Read the grams or millilitres to take.
How do you calculate normality?
Equivalent weight = molar mass ÷ n-factor
N = mass (g) × purity ÷ (equivalent weight × volume (L))
Normality of a concentrated reagent = density (g/mL) × 1,000 × assay ÷ equivalent weight
N₁V₁ = N₂V₂
Normality = molarity × n-factor. 98% H₂SO₄ is about 36.8 N (18.4 M); 37% HCl is about 12.1 N.
Worked example
With what do you want to do?: Grams needed to make a solution, chemical: Sodium hydroxide, NaOH, molar mass 40 g/mol, n-factor (equivalents per mole) 1, purity or assay 100 % w/w, target normality 0.1 N, final volume 1,000 mL:
Weigh out: 4 g
The calculator also gives equivalent weight 40 g/eq; molarity of the solution 0.1 M; final volume 1,000 mL.
Assumptions and limits
- Purity is weight percent. For hydrated salts, use the hydrate molar mass.
- n-factor depends on the reaction: KMnO₄ is 5 in acid but 3 in neutral solution.
Frequently asked questions
How do you prepare 0.1 N NaOH?
Dissolve 4.0 g of NaOH pellets in about 800 mL of distilled water, cool, and make up to 1,000 mL. Standardise against potassium hydrogen phthalate because NaOH absorbs moisture and CO₂.
How do you prepare 0.1 N H₂SO₄ from 98% acid?
Concentrated 98% sulphuric acid is about 36.8 N. Take 2.72 mL and add it slowly to about 800 mL of water, cool, then make up to 1,000 mL.
What is the difference between normality and molarity?
Molarity counts moles per litre. Normality counts reacting equivalents per litre, so N = M × n-factor. For HCl they are equal; for H₂SO₄ normality is twice the molarity.
References
- APHA, Standard Methods for the Examination of Water and Wastewater, 24th ed.
- Vogel's Textbook of Quantitative Chemical Analysis, 6th ed.