Solution Stoichiometry - Dillutions

When two solutions are mixed together the molarity changes. Dillution is the process of decreasing the concentration by adding a solvent (usually H20). The amount of solute does not change as n1 = n2. And because concentration is mol/L we can write..

• C = n/V and..
• n = CV so..
• C1V1 = C2V2

Example:

• Determine the concentration when 100mL of 0.10M HCl is diluted to a final volume of 400mL

     C1V1 = C2V2

     (0.1M)(0.100L) = C2(0.400L)

     C2 = 0.025 M

• How much water must be added to 10.0mL of 10.0M Na2SO4 to give a solution with a concentration of 0.50M?

     C1V1 = C2V2

     (10.0M)(0.010L) = (0.50M)V2

     V2 = 0.200L

              200mL - 10mL = 190mL