Question

what concentration of hydroxide ion ust be exceeded in a .01M solution of nickel(II) nitrate in order to precipitate nickel (II) hydroxide?

Answer 1

Ni(OH)2 ==> Ni^2+ + 2OH^-

Ksp = (Ni^2+)(OH^-)^2
(Ni^2+) = 0.01 in the problem.
Solve for OH^-.