What Is the pH of a Saturated Zn(OH)2 Solution?

[tua28494]

Homework Statement

What is the pH of a saturated Zn(OH)₂ solution?

Ksp = 1.2 x 10^-17

Homework Equations

Ksp = [Zn2+] [OH-]^2

Zn(OH)2 <----> Zn2+ + 2OH-

pOH = -log [OH-]

pH = 14- pOH

The Attempt at a Solution

Ksp = 1.2 x 10^-17 = [Zn2+] [OH-]^2

Zn(OH)2 <----> Zn2+ + 2OH-
- x +x +2x
1.2 x 10^-17 = [x][2x]^2 = 4x^3
x = 1.4 x 10^-6 M
[OH-] = 2x = 2.8 x 10^-6 M
pOH = - log 2.8 x 10^-6 = 5.5
pH = 14 - 5.5 = 8.5

Again I am learning this on my own and do not have a solution manual to the textbook I am using. So just s quick check would be greatly appricated. Thank you for your time.

 

[Borek]

Approach looks OK and final result seems reasonable.

Note that this is very close to the place were OH^- from water dissociation may play an important role.

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