Calculate the Number of Moles of Solute Present

Calculating Molarity

Example: What is the molarity of a solution prepared by dissolving 15.0 g of sodium hydroxide in enough water to make a total of 225 mL of solution?

 Calculate the number of moles of solute present.

mol = 15.0g NaOH x 1 mol NaOH NaOH 40.0 g NaOH mol 0.375 mol = NaOH NaOH

 Calculate the number of liters of solution present. L soln = 225 mL x 1 L = 0.225 L soln 1000 mL  Divide the number of moles of solute by the number of liters of solution.

0.375 mol M = = 1.67 M NaOH NaOH 0.225 L soln

2. What is the molarity of a solution that contains 1.724 moles of H2SO4 in 2.50 L of solution?

 Calculate the number of moles of solute present.

mol H2SO4 = 1.724 mol (given)

 Calculate the number of liters of solution present. L soln = 2.50 L (given)

 Divide the number of moles of solute by the number of liters of solution.

M = 1.724 mol = 0.690 M H2SO4 H2SO4 2.50 L soln

3. What is the molarity of a solution prepared by dissolving 25.0 g of HCl (g) in enough water to make 150.0 mL of solution?

M = 25.0 g HCl x 1 mol HCl x 1000 mL soln 150.0 mL 36.5 g 1 L soln soln HCl M = 4.57 M HCl