how to find moles of solute
3. Find the molar mass of the solute. In order to calculate the number of moles from the mass or grams of solute used, you must first determine the molar mass of the solute. This can be done by adding together the separate molar masses of each element found in the solution.ivide the number of moles by the number of liters. Now that you have the number of moles, you can divide this value by the number of liters of solution in order to find the molarity. 1  Example problem: molarity = moles of solute / liters of solution = 0.0215 mol / 5.2 L = 0.004134615.