Hello, Leya,
Let's look at the equations defined by the Ksp.
For a solubility of a compound that dissolves in water, we can write:
aA(s) = cC(aq)+dD(aq)
The solubility coefficient is defined as:
Ksp=[C]c[D]d
Now let's look at each of the questions:
1) Colbalt (II) hydroxide Co(OH)2; Ksp 5.92x10-15
Co(OH)2 = Co++ + 2OH-
Ksp = [Co++]*[OH-]2
If the concentration of Co++ is x, then OH- will be 2x. So we have:
Ksp = x3
5.92x10-15 = x3
x = 1.8x10-5
2) lead(II)chloride PbCI2 , Ksp 1.70x10-5
PbCL2 = Pb++ + 2Cl-
Ksp = [Pb++]*[Cl-]2
We have the same situation with the product concentrations, so we can again write:
Ksp = x3
1.70x10-5 = x3
x = 2.57x10-2
When we compare the two, we can see that the larger Ksp favors the products, while the lower Ksp favors the reactants.(Remember that 10-15 is smaller than 10-5, despite the initial impression :) )
Bob