Normality is molarity times the reacting capacity
Normality (N) is the number of equivalents of a substance per litre of solution. An equivalent is one unit of reacting capacity — one H+, one OH−, or one electron transferred. Multiply the molarity by n, the equivalents each molecule supplies, and you have the normality. From mass, N = mass ÷ (molar mass × n × volume in L).
Why 1 M sulfuric acid is 2 N
Same solution, two different numbers. Molarity counts the molecules; normality counts how many protons they can donate. Sulfuric acid gives two H+ per molecule, so its normality is double its molarity.
Both solutions have the same number of molecules per litre, but sulfuric acid carries twice the reacting capacity, so it is twice as normal.
Equivalents per molecule for common acids and bases
| Substance | Formula | Equivalents (n) | N for 1 M |
|---|---|---|---|
| Hydrochloric acid | HCl | 1 | 1 N |
| Nitric acid | HNO₃ | 1 | 1 N |
| Sulfuric acid | H₂SO₄ | 2 | 2 N |
| Phosphoric acid | H₃PO₄ | 1–3 | up to 3 N |
| Sodium hydroxide | NaOH | 1 | 1 N |
| Calcium hydroxide | Ca(OH)₂ | 2 | 2 N |
| Potassium permanganate | KMnO₄ | 5 | 5 N |
Phosphoric acid and redox agents like permanganate depend on the reaction: n is the number of protons or electrons actually exchanged, not always the maximum the molecule can give.
Two things people get wrong
- Volume in litres. The formula needs litres, but you often measure in millilitres. Divide by 1000 first (250 mL = 0.25 L), or the normality comes out 1000 times too small.
- Equivalent weight. To weigh out a 1 N solution, use the equivalent weight = molar mass ÷ n. For sulfuric acid that is 98 ÷ 2 = 49 g per equivalent, so 1 N needs 49 g/L, not 98.
Common questions
What is the difference between normality and molarity?
Molarity counts moles of the substance per litre. Normality counts equivalents per litre, where an equivalent is one unit of reacting capacity (one H+, one OH-, or one electron). They are linked by N = M x n, so for sulfuric acid, which gives two H+, a 1 M solution is 2 N.
How do I convert molarity to normality?
Multiply the molarity by the number of equivalents per molecule. For 0.5 M sulfuric acid, n = 2, so N = 0.5 x 2 = 1 N. For any acid or base with a single reacting group, n = 1 and normality equals molarity.
What does a "1 N solution" mean?
It contains exactly one equivalent of the substance per litre. For HCl (n = 1) that is the same as 1 M. For sulfuric acid (n = 2) it is only 0.5 M, because each molecule supplies two equivalents.
