[VOH]

1. Mixture of Na2S and sodium chloride is dissolved in water and through it, was it conducted Cl2. Featured is the 0.205 g sediment. The remaining solution is acidify with  nitric acid and AgNo3 was added to whiskey. Provided by the 3.560 g sediment. Calculate the mass proportion of Na2S and NaCl in the sample.
2.What volume of barium chloride concentration of 2 mol / l should be added to 100 l KNH4SO4 (C = 0.01 mol / l) to a) start a deposition sulfate b) the sulfates are quantitatively calm?

[Borek]

Please read forum rules.

You just don't ask. You try, you tell us what you did, we push you in the right direction.

[VOH]

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?

[Borek]

pH is 12, that defines concentration of OH^-.

I resolved these two tasks

In English: you solved two questions.

[VOH]

Yes, I know that. But when I insert that in equation I do not get the correct solution.

[Borek]

Perhaps there is an error in the key and they want you to assume just another complexation equilibrium?