Question

Calculate the concentration of hydroxide ions in solution if 1.52g of magnesium hydroxide was dissolved in water to make a saturated solution.

For reference, I didn't use Ksp, I calculated the moles. My final answer was around 0.3 something, moles/L I don't remember. Could anyone please help as my friends and I are divided over the answer.

Answer 1

The concentration of hydroxide ions ([OH-]) in a saturated solution of magnesium hydroxide (Mg(OH)2) with a Ksp of 5.6 x 10^-12 is 2.2 x 10^-4 M, considering the stoichiometric relationship in the dissolution reaction.

Step-by-step explanation:

To calculate the concentration of hydroxide ions ([OH-]) in a saturated solution of magnesium hydroxide (Mg(OH)2), we need to use the solubility product constant (Ksp), given that the dissolution of Mg(OH)2 is represented by Mg2+ (aq) + 2OH- (aq). Here, we have a saturated solution, which implies that the dissolved magnesium hydroxide is in dynamic equilibrium with undissolved Mg(OH)2 at this point.

The Ksp equation for this equilibrium would be Ksp = [Mg2+][OH-]2. Given the Ksp for Mg(OH)2 as 5.6 x 10^-12 and using the stoichiometry of the dissolution reaction, where every mole of Mg2+ yields two moles of OH- ions, if [Mg2+] = 1.1 x 10^-4 M, then [OH-] would be approximately 2.2 x 10^-4 M, since the ratio of Mg2+ to OH- is 1:2.

Hence, the concentration of hydroxide ions in the solution, accounting for stoichiometry, is 2.2 x 10^-4 M.