Question

What volume of 0.5 M CaCl2 solution is needed to prepare 250 ml of solution that has Cl- concentration 0.1M?

Answer 1

First we need to calculate the Molarity of the CaCl₂ from the molarity of the Cl⁻ ions.

Molarity  of CaCl₂ in the concentration of 0.1M Cl⁻ is 

                                                           0.1M / 2 = 0.05M of CaCl₂

Using the equation of M₁V₁ = M₂V₂ to the volume required of the 0.5M CaCl₂

(Where M₁ is the molarity of the concentrated solution, V₁ is the volume of the concentrated solution while M₂ is the concentration of the dilute solution and V₂ is the volume of the dilute solution)

The volume required:

               M₁V₁ = M₂V₂ 

             0.5M × V₁ = 0.05M × (250/1000 = 0.25)

              V₁ = 0.05 × 0.25 / 0.5

                   =  0.025 L

Therefore the volume required of the 0.5 M CaCl₂ is 0.025L or 25ml