Find pH given solubility constant Ksp? Need help with this problem?

A metal plating solution contains 50 mg/l of copper. Determine the concentration, in moles/L, to which hydroxide concentration must be raised to precipitate all but 1.3 mg/l of the copper using lime. The Ksp of copper hydroxide is 2 x 10^-19. Find the final pH. Ok so I know the equation to use is: Ksp = [Cu]... show more A metal plating solution contains 50 mg/l of copper. Determine the concentration, in moles/L, to which hydroxide concentration must be raised to precipitate all but 1.3 mg/l of the copper using lime. The Ksp of copper hydroxide is 2 x 10^-19. Find the final pH.

Ok so I know the equation to use is:
Ksp = [Cu] [OH}^2

Do I need to subtract 1.3 mg/l from 50 mg/l and convert that to moles/L of Cu. For the final pH, I get 6.21. Is my answer is correct?
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