Consider a solution of CaCl2 and Mg(NO3)2 in which the concentrations of both Mg2+ and Ca2+ are the same, 0.01. M. Is it possible to separate Ca2+ from Mg2+ by selective precipitation of Mg(OH)2? To be precise, is it possible to precipitate 99.99% of magnesium without precipitating any calcium as hydroxides? For the sake of simplicity, assume that the precipitation reactions do not result in any change of the volume of the reaction mixture. The Ksp values of the calcium and magnesium hydroxides are 6.5 x 10-5 and 7.1 x 10-12, respectively.

I don't have access to my textbook right now (im on mobile) so I cant do much work on this. Please help, I'm SO lost.

To determine if it is possible to selectively precipitate Mg(OH)2 and separate calcium from magnesium, we need to compare the solubility product constants (Ksp) of calcium hydroxide (Ca(OH)2) and magnesium hydroxide (Mg(OH)2).

The solubility product constant (Ksp) is an equilibrium constant that represents the degree to which a sparingly soluble salt will dissolve in water. It is defined as the product of the concentrations of the ions in the equilibrium expression, each raised to the power of their stoichiometric coefficients.

The balanced equations for the precipitation reactions of Ca(OH)2 and Mg(OH)2 are as follows:

Ca(OH)2(s) ⇌ Ca2+(aq) + 2OH-(aq)
Ksp = [Ca2+][OH-]^2

Mg(OH)2(s) ⇌ Mg2+(aq) + 2OH-(aq)
Ksp = [Mg2+][OH-]^2

To determine if it is possible to selectively precipitate Mg(OH)2 while keeping Ca(OH)2 in solution, we need to consider the relative values of the Ksp of Ca(OH)2 and Mg(OH)2.

Given that the Ksp of Ca(OH)2 is 6.5 x 10^-5 and the Ksp of Mg(OH)2 is 7.1 x 10^-12, it is clear that Mg(OH)2 is much less soluble than Ca(OH)2. This means that, under normal conditions, Mg(OH)2 will have a lower concentration in solution compared to Ca(OH)2.

Therefore, it is possible to selectively precipitate Mg(OH)2 from the solution while keeping Ca2+ in solution. By carefully adjusting the pH of the solution to increase the hydroxide ion concentration, Mg(OH)2 will precipitate out while Ca2+ remains in solution.

To achieve a high level of selectivity and precipitate 99.99% of magnesium without precipitating any calcium, you would need to maintain the pH within a narrow range that favors the precipitation of Mg(OH)2 while not exceeding the solubility limit of Ca(OH)2. This can be achieved through careful control of the pH and the addition of a precipitating agent such as ammonia or sodium hydroxide.

It is important to note that practical considerations such as the presence of other ions in the solution, formation of complex ions, and the formation of amphoteric metal hydroxides may affect the selectivity and efficiency of the precipitation process. Additionally, experimental verification and further calculations should be done to determine the exact conditions required to achieve the desired level of separation.