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Ksp for Cu(OH)2 is 2.6 x 10-19. If a solution is 0.010 M with respect to Cu2+, w

ID: 758527 • Letter: K

Question

Ksp for Cu(OH)2 is 2.6 x 10-19. If a solution is 0.010 M with respect to Cu2+, what must be the hydroxide ion concentration in order for precipitation to begin?

Explanation / Answer

First of all, always write the dissociation reaction: Cu(OH)2 (s) --> Cu 2+ (aq) + 2OH - (aq) Ksp is the equilibrium constant for this reaction (remember, you ignore solids or pure liquids). Ksp = [Cu 2+] * [OH -]^2 For every mole of Cu(OH)2, you get one mole of Cu 2+ and two moles OH- as the equation indicates so let [Cu 2+] = x and [OH-] = 2x Ksp = x * (2x)^2 2.6 * 10^-19 = 4x^3 x = 4.0 * 10^ -7 Remember [OH-] = 2x so [OH-] = 8.0 * 10^-7 M