If you place 5 mg NiCO3 in 1 L of pure water, does all the salt dissolve? If not, how much salt remains undissolved? The Ksp for NiCO3 is 6.6x10^-9 M.

Answer 1

........NiCO3 ==> Ni^2+ + CO3^2-
I.......solid.....0........0
C.......solid.....x........x
E.......solid.....x........x

Substitute the E line into the Ksp expression and solve for x = (NiCO3) in mols/L.
Then grams = mols x molar mass = ?
Compare the solubility with the 5 mg you have.