The molar solubility of magnesium chloride in water is 0.23 M.

Question

What is the numerical value for Ksp for MgCl2?
Suppose you wanted to reduce the concentration of dissolved Mg2+ to 0.00537 M by adding NaCl. What concentration of NaCl would you need?

Answer 1

MgCl2 ==> Mg^2+ + 2Cl^-
.........0.23....0.46
Substitute those number into the Ksp expression and solve for Ksp.

part 2.
Then Ksp = (Mg^2)(Cl^-)^2
Plug in 0.00537 for Mg^2+ and solve for Cl^-.