How to use it
- Choose to start from the molarity or from the mass and volume.
- Pick the substance. For anything not listed, choose “Other substance” and enter its molar mass and how many H⁺, OH⁻ or electrons one formula unit exchanges.
- Enter the molarity, or the grams dissolved and the final volume of the solution.
Formulas
- Equivalent weight: Eq = M ÷ n (g/eq).
- From molarity: N = Molarity × n.
- From mass: equivalents = mass ÷ Eq; N = equivalents ÷ volume in litres.
- mEq/L = N × 1000.
Molar masses of the presets are worked out from the standard atomic weights (for H₂SO₄: 2 × 1.008 + 32.06 + 4 × 15.999 = 98.072 g/mol).
Worked example
0.5 M sulfuric acid: N = 0.5 × 2 = 1 N, which is 1,000 mEq/L, and the equivalent weight is 49.036 g/eq.
4.9 g of H₂SO₄ made up to 500 mL: 4.9 ÷ 49.036 = 0.099927 eq; divided by 0.5 L that is 0.199853 N (a 0.099927 M solution).
4 g of NaOH (39.997 g/mol) in 1 L: 4 ÷ 39.997 = 0.100008 N.
Tips
- Volume of solution, not of water. Dissolve and then make up to the mark.
- Same acid, different n. Phosphoric acid titrated only to its first end point acts as 1 equivalent, not 3; enter the n that matches your reaction.
- Titration shortcut. At the end point N₁V₁ = N₂V₂, which is why normality is handy for titrations.