To calculate molarity, the moles of solute must be divided by the volume of solution in liters. The unit of molarity is reported in moles/liter or molar.
- Calculate the moles of solute
If the moles of solute are not given, then convert the mass of the solute from grams to moles. The mass can be obtained by weighing the solute on a scale. Obtain the molecular weight of the solute from the periodic table. Divide the grams of solute by the molecular weight. This value is the number of moles present in the solute.
- Calculate the volume of solution in liters
The volume of solution should be calculated. If not given, the volume can be measured through the use of a volumetric flask or beaker. It is important to make sure this is the final volume of solution, not the volume of the solute or solvent.
- Divide the moles of solute by the volume of solution
Take the number of moles of solute obtained in Step 1 and divide it by the total liters of the final solution obtained in Step 2. This value represents the molarity of the solution. The final unit must be in molar, signified by M.