Question

Calculate the Ksp of a saturated solution of Mg(OH)2 upon titration with 0.0100 HCl in the presence of phenolphthalein indicator utilizing the data below.

mL saturated Mg(OH)2 titrated - 1382
mL of 0.0100 M HCl to endpoint - 38.7

Please help me and show how you solve this.

Answer 1

Let's work in millimoles. mols = L x M and millimols = mL x M
millimols HCl used = mL x M = 38.7 x 0.01 = 0.387
So millimoles OH = 0.387
(OH^-) in molarity = millimoles/mL = 0.387/1382 = ?approx 3E-4 but that's an estimate.
......................Mg(OH)2 ==> Mg^2+ + 2OH^-
.......................solid..............(3E-4)/2....3E-4

Plug the concns of Mg and OH into the Ksp expression and solve for Ksp.
Post your work if you get stuck.