Molarity (M) is a concentration unit indicating the moles of solute dissolved in one liter of solution — the most widely used concentration notation in chemistry labs.
Enter the moles of solute (mol) and the volume of solution (L) to calculate the molarity (mol/L, M).
For example, dissolving 1 mol of solute to make a total volume of 2 L gives a molarity of 0.5 M.
Molarity (M) is the concentration of a solution: moles of solute per litre of solution. It is the standard way of expressing concentration in laboratory chemistry and the basis for dilution and titration calculations.
Enter the moles of solute and the solution volume in litres to get the molarity.
Molarity is moles of solute per litre of solution, written mol/L or M. A 0.9 % saline drip is about 0.154 mol/L sodium chloride, and seawater is roughly 0.6 mol/L in total dissolved salts. Because the volume of a liquid expands with temperature, high-precision work uses molality (moles per kilogram of solvent) instead.
M = n (mol) / V (L)Molarity is moles per litre of solution, while molality is moles per kilogram of solvent. Molarity changes slightly with temperature because the solution expands; molality does not, so it is preferred for precise work.
Work out the moles you need from the volume, convert to grams with the molar mass, dissolve the solid in a little solvent, then top up to the final volume in a volumetric flask — always make up to volume last.
You need 0.250 × 0.5 = 0.125 mol, which is 0.125 × 58.44 = 7.31 g. Dissolve the salt in rather less than 250 mL of water, then top up to the mark, because it is the final solution volume that defines the concentration.
The solute amount is fixed but the solution volume expands when warm, so the same moles occupy more space and the concentration falls. Molality uses the mass of solvent, which does not change with temperature.
2026-10-19