Question

The hydroxide ion has the formula OH?. The solubility-product constants for three generic hydroxides are given here.

Generic hydroxide	Ksp
XOH	1.60

Answer 1

#immitate this

In the question, it tells you that the Ksp for Y(OH)2 is 2.10 x10^-10, so first write out the Ksp equation:

Ksp = [Y2+][OH-]^2
Also, it tells you that in order for the removal of an ion to be considered complete, its concentration must be 1.0x10^-6. So you know:
[Y2+] = 1.0x10^-6

Plugging all this into the Ksp equation above, you get:

Ksp = [Y2+][OH-]^2
2.10 x10^-10 = (1.0x10^-6)[OH-]^2
[OH-] = 0.0145

B) For this part, it tells you that pH= 10.5, so you can calculate [OH-] in the following way:

pOH = 14- pH
= 14-10.5
= 3.5
[OH-] = antilog(-3.5)
= 0.000316 M

From here, you can calculate the amount of X, Y, and Z, using the following equations:
(1) Ksp = [X][OH-] ---> solve for x
(2) Ksp = [Y2+][OH-]^2 ---> solve for y
(3) Ksp = [Z3+][OH-]^3 ---> solve for z

the values you get for X, Y, and Z will tell you the concentration of the cations.
I will let you solve for [X], [Y], and [Z], but the answer you should get is:

Highest -----------> Lowest

Y, Z, X