You are right. More effective is when we discuss.I resolved these two tasks, but I need help with the following: In a solution volume of 100 cm3 concentracion of Mg and Ca are the same and the amount 0.01 mol/dm3. The solution of EDTA whit 10 times higher concentration is added. Calculate concentration of Mg and Ca at the point of equivalence on pH 12. For the Ca I did over the formula for conditional stability constant and got a good solution, and for Mg as magnesium will be as much as let it sediment, I worked through the solubility product Ksp (Mg (OH) 2) = 6 * 10-10

Ksp= C(Mg2+)*C(OH-)2, Ksp=R*(2R)2=4R3 R=5.3 *10-4 R is dissolubility but I do not know how to calculate concentration for Mg.

Solution should be 2.45 *10-5 mol/dm3 .Can you help me about Mg?