What concentration of Mg 2+ ions will reImain in solution after adding NaOH to a solution composed of 200.0mL of 0.01M Mg 2+ and 0.005M Ca2+?

Question

What concentration of Mg 2+ ions will remain in solution after adding NaOH to a solution composed of 200.0mL of 0.01M Mg 2+ and 0.005M Ca2+?

Answer 1

We need to know the Ksp for Mg(OH)₂ and for Ca(OH)₂.

You have the following situation:

Mg²⁺ + 2NaOH ==> Mg(OH)₂(s) + 2Na⁺(aq)

Ca²⁺ + 2NaOH ==> Ca(OH)₂(s) + 2Na⁺(aq)

To find [Mg²⁺] remaining after addition of NaOH, one needs to know the Ksp for Ca(OH)₂ assuming it precipitates first, and then also the Ksp for Mg(OH)₂.