The dissolution of magnesium hydroxide in water is represented by the ionic equilibrium
Mg(OH)2(s)⇌Mg2+(aq)+2OH−(aq)ΔH∘=+37kJmol−1
Consider the following independent actions applied to saturated seawater at 298 K that is initially at equilibrium with excess solid Mg(OH)2 present.
I. Add 10.0 mL of 6.0 M NaOH to one liter of the suspension.
II. Dilute the suspension by adding one liter of pure water.
III. Bubble carbon dioxide gas through the mixture, producing the reaction OH−+CO2→HCO3−.
IV. Increase the temperature to 310 K while keeping volume constant.
V. Remove a portion of the solid Mg(OH)2 while leaving the solution volume unchanged.
a. Rank actions I–V and an untreated control (VI) from lowest to highest concentration of Mg2+ at the new equilibrium.
b. For each action, explain the chemical reasoning that led to its placement in your ranking, referencing shifts in equilibrium, ion–product considerations, and heat effects where appropriate.
c. State which actions, if any, cause a change in the numerical value of the solubility product Ksp, and justify your answer.