The concentration of a solution is generally measured in molarity. To determine the molarity of a solution, divide the number of moles of solute by the volume of the solution in liters.
- Determine the weight of the molecule
Use a scale to obtain the weight of the solute before the solution has been mixed. This weight should be determined in grams.
- Obtain the molecular weight of the solvent
Use a periodic table to find the molecular weight of the solute by adding together the molecular weights of each individual element present in the solute. This value is given in grams.
- Convert from grams to moles
Divide the weight of the solute obtained in Step 1 by the molecular weight of the solute obtained in Step 2. Because 1 mole is equal to the molecular weight in grams, the grams unit cancels, and the resulting answer is the moles of solute.
- Determine the volume of the solution
A solute is added to a solvent to create a solution. The volume of the solution can be measured in a volumetric container, such as a volumetric flask or beaker. It is necessary that this value be determined in liters. If the volume is given in milliliters, it can be divided by 1000 to determine the value in liters.
- Divide the moles by the volume
Divide the value of the moles of solute obtained in Step 3 by the liters of solution obtained in Step 4. This value is moles/L, which is also known as molarity.