Normality vs molarity and equivalents
How normality and molarity differ, what an equivalent is, and when eq/L is the more useful way to describe a solution.
Counting moles versus counting equivalents
Molarity counts moles of solute per litre of solution, treating every molecule as one unit. Normality counts reactive equivalents per litre instead, where an equivalent is one unit of reacting capacity such as a single proton, hydroxide ion or electron. A mole of sulfuric acid can donate two protons, so one mole of it is two equivalents. That is why the same bottle can be labelled 1 M and 2 N at the same time without any contradiction.
What an equivalent means for acids, bases and redox
For an acid the equivalence factor is the number of acidic protons it can release: 1 for HCl, 2 for sulfuric acid and 3 for phosphoric acid. For a base it is the number of hydroxide ions or protons it can accept, so Ca(OH)2 has a factor of 2. In a redox reaction the factor is the number of electrons transferred per mole of the species. Choosing the correct factor is the whole skill of using normality, because the arithmetic itself is just one multiplication.
Why titration chemists like normality
At the equivalence point of a titration the equivalents of acid equal the equivalents of base, which leads to the compact rule N1 times V1 equals N2 times V2. Because normality already folds in each substance's reacting capacity, you can compare a diprotic acid with a monoprotic base directly, without separately tracking mole ratios. That convenience is why analytical procedures and older textbooks often specify a reagent as 0.1 N rather than a molarity.
Converting between the two
To turn molarity into normality, multiply by the equivalence factor: a 2 M sulfuric acid solution is 2 times 2, or 4 N. To go the other way, divide the normality by the factor: 6 N phosphoric acid is 6 divided by 3, or 2 M. When the factor is 1 the two numbers coincide, which is a useful sanity check. This tool automates both directions and keeps the equivalence factor visible so you always see which value drove the result.