How it works
Molarity measures how concentrated a solution is — moles of solute per litre of solution. The same relationship rearranges to give moles or volume instead, depending on which two values you already know.
molarity = moles ÷ volume
moles = molarity × volume
volume = moles ÷ molarity
moles = mass ÷ molar mass — when starting from a weighed-out amount
Worked example
Dissolving 1 mole of solute into 2 litres of solution.
- Divide moles by volume: 1 ÷ 2.
- That gives 0.5.
The molarity is 0.5 M. (58.44 g of table salt, NaCl, is 1 mole — so 58.44 g dissolved to make 2 L would give the same 0.5 M solution.)
Common questions
What's the difference between molarity and molality?
Molarity is moles per litre of solution; molality is moles per kilogram of solvent. They're close for dilute aqueous solutions but diverge as concentration rises, since solute takes up its own volume.
Where do I find a compound's molar mass?
Add up the atomic masses of every atom in its formula from the periodic table — for NaCl that's sodium (≈22.99) plus chlorine (≈35.45), giving about 58.44 g/mol.
Does volume mean the volume of solvent I start with?
No — it's the volume of the final solution after the solute is fully dissolved and topped up, which is usually slightly more than the starting solvent volume alone.