Question

QUESTION 20 What is the molar solubility of Mg(OH)2 in a basic solution with a pH of 12.00? Ksp for Mg(OH)2 is 5.60E-10 Enter your answer in exponential (E) format (sample 1.23E-4) with one decimal place and without units.

please give answer in the format asked

Answer 1

Answer -

Given,

pH = 12.00

Ksp = 5.60E-10 or 5.60 * 10-10

Molar Solubility of Mg(OH)2 = ?

We know that,

pH + pOH = 14

So,

pOH = 14 - pH --------A

Also,

pOH = - log [OH-] --------------B

from A and B,

-log[OH-] = 14 - pH

log[OH-] = pH- 14

Now,

10log[OH-] = 10(pH-14)

[OH-] = 10(pH-14)

Put the value of pH,

[OH-] = 10(12.00-14)

[OH-] = 10-2 M ----------------- X

Now,

Mg(OH)2 (s) ⇌ Mg2+(aq) + 2OH− (aq)

solids and liquids are not considered to calculate Ksp

So,

Ksp = [Mg2+] [OH-]2

Put the X and Ksp in this,

5.60 * 10-10 = [Mg2+] (10-2)2

5.60 * 10-10 = [Mg2+] (10-2)2

[Mg2+] = 5.60 * 10-10 / (10-2)2

[Mg2+] = 5.60 * 10-10 / (10-4)

[Mg2+] = 5.60 * 10-6 M

Mg(OH)2 (s) ⇌ Mg2+(aq) + 2OH− (aq)

Using Stiochiometry, it can be analyzed that molar ratio of Mg(OH)2 and Mg2+ is 1:1.

So, Molar Solubility of Mg(OH)2 is 5.60 * 10-6 M [ANSWER]