Enter the mass of solute, its molar mass, and the solution volume to get the molarity, mass concentration, and moles. Add the solvent mass or the solution density for molality and mass percentage as well.
Not sure of the molar mass? Add up the atomic masses of every atom in the formula, or look them up with the Periodic Table Lookup tool.
Only needed if you have not entered a solvent mass above. If both are left blank, the mass percentage cannot be calculated.
Enter the mass of solvent above to calculate molality.
Enter the mass of solvent or the solution density above to calculate the mass percentage.
This calculation assumes an ideal dissolution with no volume contraction and no complex ionic interaction between species, which is accurate enough for dilute solutions but only approximate for concentrated ones.
Concentration calculations for GCSE and A-level Chemistry
Concentration is one of the first quantitative ideas UK Chemistry students meet, from GCSE titration sums through to A-level moles and molarity questions. This calculator starts from the mass of solute and its molar mass to find the number of moles, then converts that into molarity, mass concentration in g/L, and, if you supply the solvent mass or the solution density, molality and mass percentage as well. Molarity is written mol/L or M (with a capital M sometimes used as shorthand, though it does not appear in exam mark schemes), and A-level papers occasionally use dm3 instead of L, which is the same volume.
Key formulas
| Quantity | Formula | Unit |
|---|---|---|
| Moles (n) | mass of solute / molar mass | mol |
| Molarity | n / volume of solution (L) | mol/L |
| Mass concentration | mass of solute / volume of solution (L) | g/L |
| Molality | n / mass of solvent (kg) | mol/kg |
| Mass percentage | (mass of solute / total mass of solution) x 100 | % m/m |
What this calculator cannot do
The results assume the solute dissolves fully and ideally, with no change in total volume on mixing and no interaction between dissolved species. Strong electrolytes dissociate into ions, which affects properties such as conductivity or freezing-point depression, but this tool works with the concentration of the solute as dissolved, not the resulting ion concentrations. Weak acids and bases that only partially dissociate need an equilibrium calculation this tool does not attempt. Mass percentage without a density value is only calculated when a solvent mass is entered, since the total solution mass otherwise cannot be worked out from volume alone.
A worked example
To prepare 500 mL of a 0.5 mol/L sodium chloride solution, first find the mass needed: n = molarity x volume = 0.5 x 0.5 = 0.25 mol, then mass = n x molar mass = 0.25 x 58.44 = 14.61 g of NaCl, made up to 500 mL with water. Enter 14.61 g, a molar mass of 58.44 g/mol, and 500 mL above to check this. For the molar mass of any element in a formula, the Periodic Table Lookup tool gives the exact atomic mass to use.