[AllHallows20]

This is the question I'm trying to answer:
If a 0.100 M solution of NaOH is added to a solution containing 0.200 M Ni2+, 0.200 M Ce3+, and 0.200 M Cu2+, which metal hydroxide will precipitate first? Ksp for Ni(OH)2 = 6.0 X 10-16, Ksp for Ce(OH)3 = 6.0 X 10 -22, and Ksp for Cu(OH)2 = 4.8 x 10-20.

I know to first calculate when each of the metals will precipitate but I can't seem to get that to work out correctly

[Borek]

Calculate - for each metal separately - concentration of OH^- needed for precipitation.

[AllHallows20]

I'm attempting that but I'm pretty sure I'm doing it wrong, I used the formula  ksp=[2.00M][1.00x]^2 for Ni and cu and to the 3rd power for ce

[Borek]

You are doing strange things.

Write Ksp formula for Ni(OH)₂.

[AllHallows20]

6.0X10^-16=[Ni][OH]^2

[Borek]

OK, what is Ni²⁺ concentration?

[AllHallows20]

.200 M

[Borek]

So, what is OH^- concentration needed for precipitation?

[AllHallows20]

.200 M?

[AllHallows20]

no wait would it be .4M

[Borek]

Why do you guess instead of calculating? Plug Ni²⁺ concentration into the formula and solve for the only unknown - [OH^-]. Basic algebra.

[AllHallows20]

oh jeeze, thanks I have no idea how I made things so much more complicated than they had to be.