Calculate the molar solubility of Mg(OH)2 in the following solvents:
(i) 8.60×10−2M MgCl2
(ii) 3.70×10−2M KOH(aq)
Please help!!!
This is parts 2 and 3 of your former post. These are common ion problems; otherwise, they are worked the same way.
To calculate the molar solubility of Mg(OH)2 in the given solvents, we need to use the concept of the solubility product constant (Ksp). Ksp is the equilibrium constant for the dissociation of a sparingly soluble compound in a solution.
The chemical equation for the dissociation of Mg(OH)2 is:
Mg(OH)2(s) ⇌ Mg2+(aq) + 2OH-(aq)
The Ksp expression for this dissociation is:
Ksp = [Mg2+][OH-]^2
(i) 8.60×10−2M MgCl2:
When MgCl2 is dissolved in water, it dissociates into Mg2+ and Cl- ions. Since Cl- is a common ion with Mg(OH)2, it will affect the solubility of Mg(OH)2. To calculate the molar solubility, we need to consider the common ion effect.
The initial concentration of Mg2+ ion in the solution is 8.60×10−2M. However, due to the common ion effect, some of the Mg2+ ions will react with OH- ions, forming Mg(OH)2 that will precipitate.
Let's assume the molar solubility of Mg(OH)2 is "x". Thus, the concentration of Mg2+ ions in the solution will be (8.60×10−2 - x) M, and the concentration of OH- ions will be 2x M.
Using the Ksp expression, we can write:
Ksp = (8.60×10−2 - x)(2x)^2
Solving this equation for x will give us the molar solubility of Mg(OH)2 in the given solvent.
(ii) 3.70×10−2M KOH(aq):
When KOH is dissolved in water, it completely dissociates into K+ and OH- ions. Only OH- ions will react with Mg2+ ions to form Mg(OH)2.
The concentration of OH- ions in the solution is 3.70×10−2M. The concentration of Mg2+ ions will depend on the molar solubility of Mg(OH)2, so let's consider it as "y".
Using the Ksp expression, we can write:
Ksp = (y)(3.70×10−2)^2
Solving this equation for y will give us the molar solubility of Mg(OH)2 in the given solvent.
Please note that to obtain an accurate value for the molar solubility, you need to solve these equations using an appropriate method such as setting up an ICE table or using a quadratic equation solver.