Question

1. Mg(OH)2 is a sparingly soluble compound, in this case a base, with a solubility product, Ksp, of 5.61×10−11. It is used to control the pH and provide nutrients in the biological (microbial) treatment of municipal wastewater streams. Based on the given value of the Ksp, what is the molar solubility of Mg(OH)2 in pure H2O?

Answer = Mol Solubility = 2.41 x 10^-4

2. Based on the given value of the Ksp, what is the molar solubility of Mg(OH)2 in 0.130 M NaOH? Express your answer with the appropriate units.

3. What is the pH change of a 0.300 M solution of citric acid (pKa=4.77) if citrate is added to a concentration of 0.170 M with no change in volume? Express the difference in pH numerically to two decimal places.

Answer 1

Answer to the problem For mg6Hh we have the following equilibrium Mg(OH)₂ = Mgt2 + 20H ; Let the schbility of s 25 mg6uh is s (ND [ngtys Tox1 = 25 Schubility product, keep = tungth 1 tot ² Ke = 5:61x10" or 5. 61x10 - (5) x (29) 2 or 45% = 5.61 x 10" a 5% = 5.61 x 10" om s - (5.61 x 16" ); ^. 5 = Esperanto 2.41X1074 M Solubility of Mgot in pure water 2:41x109 M. Aus

2. new solubility of Ma Colf in 0.130 M NAOH Let is the s'. Mg(OH)2 4 Mg + 204 [M9+] = 5 C = Concentration of Nash ToH7 = 25+ c = 25 +0.130 Kep= 5.61x10" solubility product, Kex = lngth 1 10H2² • 5-61x7" = ($')(26+0-180), Assuming 26 LL 0.130 5. 61 x 10" = x (0130) or, Ś = 5.61X10" 0.0109 or é = 3.3 2.10 m Molar solubility of Mg(OH)2 in 0.130 M NaOH is 3.32x10 m Ans.