Question

Part B -

Calculate the molar solubility in NaOH Based on the given value of the Ksp, what is the molar solubility of Mg(OH)2 in 0.160 M NaOH?

Express your answer with the appropriate units.

Part D

What is the pH change of a 0.210 M solution of citric acid (pKa=4.77) if citrate is added to a concentration of 0.175 M with no change in volume?

Express the difference in pH numerically to two decimal places.

Answer 1

part B)

[OH-] = 0.160 M

Mg(OH)2 , Ksp = 5.61 x 10^-12

Mg(OH)2 -------------------------> Mg+2 + 2OH-

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

5.61 x 10^-12 = (S ) (0.160)^2

S = 2.19 x 10^-10 M

molar solubility = 2.19 x 10^-10 M

part D)

initial pH = 1/2 [pKa -logC]

pH = 1/2 [4.77 - log0.210]

pH = 2.72

new pH

pH = 4.77 + log (0.175 / 0.210)

pH = 4.69

pH change =   4.69 - 2.72

                  = 1.97

pH change = 1.97