Calcium chloride dissociates as follows:
CaCl₂(s) ⇄ Ca²⁺(aq) + 2Cl⁻(aq)
According to the dissociation equation, it can be seen that CaCl₂ and Cl⁻ ions have stoichiometric ratio:
n(CaCl₂) : n(Cl⁻) = 1 : 2
n(CaCl₂) = n(Cl⁻)/2
So, it is necessary 2 times more moles of calcium chloride for producing 1 mole of Cl⁻.
n(CaCl₂) = 0.252/2 = 0.126 mole
Finally, we can calculate the necessary mass of calcium chloride:
m(CaCl₂) = n x M = 0.126 x 110.98 = 13.98 g of CaCl₂