Question

A stock solution of MgCl2 (MM=95.21g/mol) is prepared by dissolving 5.25g sample to make a 500.0ml aqueous solution. If a 5.00ml aliquot diluted to 100.0ml, what is the molar concentration of this new MgCl2?

Answer 1

Ans. # Stock solution:

            Moles of MgCl₂ = Mass/ Molar mass

                                                = 5.25 g / (95.21 g/ mol)

                                                = 0.0551413 mol

Molarity of solution = Moles of MgCl₂ / Volume of solution in liters

                                    = 0.0551413 mol / 0.500 L

                                    = 0.1102826 M

# Solution 2: 5.0 mL of stock solution is diluted to 100.0 mL to make solution 2.

Now,   Using C1V1 (stock solution) = C2V2 (solution 2)

            Or, 0.1102826 M x 5.0 mL = C2 x 100.0 mL

            Or, C2 = (0.1102826 M x 5.0 mL) / 100.0 mL

            Or, C2 = 0.00551413 M

Hence, [MgCl₂] in solution 2 = 0.00551413 M