Question #c548d

1 Answer
Sep 18, 2015

Question 1: Ksp=1.1×1011

Question 2: s=4.9×1012M

Explanation:

Quest (1) determine the ksp for magnesium hydroxide Mg(OH)2 where the molar solubility of Mg(OH)2 is 1.4×104M?

We will use ICE table to solve this question.

The dissolution of Mg(OH)2 can be written as follows:

Mg(OH)2(s)Mg2+(aq)+2OH(aq)
Initial: 0M 0M
Change: sM +sM +2sM
Equilibrium: sM 2sM

The expression of Ksp can be written as follows:

Ksp=[Mg2+(aq)][OH(aq)]2

Ksp=s(2s)2=4s3=4×(1.4×104)3

Ksp=1.1×1011

Quest (2) The Ksp for Zn(OH)2 is 5.0×1017 . Determine the molar solubility of Zn(OH)2 in a buffer solution with a pH of 11.5?

We will use ICE table to solve this question.

pH=11.5[H+]=1011.5

[OH]=102.5=3.2×103M

The dissolution of Zn(OH)2 can be written as follows:

Zn(OH)2(s)Zn2+(aq)+2OH(aq)
Initial: 0M 3.2×103M
Change: sM +sM +2sM
Equilibrium: sM (3.2×103+2s)M

The expression of Ksp can be written as follows:

Ksp=[Zn2+(aq)][OH(aq)]2

5.0×1017=s(3.2×103+2s)2

Solve for s=4.9×1012M

Here is a video that explains the solving of Q2 (start at minute 5:14):