Question

The hydroxide ion has the formula OH−. The solubility-product constants for three generic hydroxides are given here.

Generic hydroxide	Ksp
XOH	1.70×10−8
Y(OH)2	2.70×10−10
Z(OH)3	8.30×10−15

The removal of an ion is sometimes considered to be complete when its concentration drops to 1.00×10−6  M. What concentration of hydroxide would cause Y2+ to "completely" precipitate from a solution?

Answer 1

concentration of hydroxide = 0.0164 M

Explanation

K_sp Y(OH)₂ = 2.70 x 10^-10

For complete precipitation of Y(OH)₂, concentration of Y²⁺ = [Y²⁺] = 1.00 x 10^-6 M

K_sp Y(OH)₂ = [Y²⁺][OH^-]²

2.70 x 10^-10 = (1.00 x 10^-6 M) * [OH^-]²

[OH^-]² = (2.70 x 10^-10) / (1.00 x 10^-6 M)

[OH^-]² = 2.70 x 10^-4

[OH^-] = (2.70 x 10^-4)^1/2

[OH^-] = 0.0164 M