consider the following equilibrium:
Mg(OH)2(aq) <-> Mg2+ (aq) + 2OH-(aq)
a) what would happen to the equilibrium if some acid is added to the soultuion?
--->OH- would increase causing Mg(OH02 to dissolve
b) what would happen to the solubility of Mg(OH)2?
---> it would increase
c) what would happen to the Ksp?
--> I don't know about this part??
I want to quibble a little with your answers. Technically a is incorrect because you are talking about OH and the question is asking what happens to th equilibrium. I would like to see you say that the equilibrium will shift to the right. You are correct that Mg(OH)2 will dissolve. Also, I wonder if you missed the point with adding acid. Adding H3O^+ to OH^- causes the reaction H3O^+ + OH^- ==> 2H2O to occur. That REMOVES OH- so the Mg(OH)2 reaction you show shifts to the right in order to REPLACE the OH^- that has been removed by the acid.
Your answer to b is right.
c. Ksp does not change (unless temperature changes, either up or down). That's why we can use Ksp in these calculations because, at constant T, K is constant.
To determine what would happen to the equilibrium, solubility, and Ksp if acid is added to the solution, let's break it down step by step:
a) What would happen to the equilibrium if some acid is added to the solution?
When an acid is added to the solution, the acid will react with the OH- ion present. This reaction can be represented as follows:
H+ (acid) + OH- (from Mg(OH)2) <-> H2O
This reaction will shift the equilibrium to the left, consuming some of the OH- ions. Since OH- ions are being consumed, the reverse reaction will be favored to maintain the equilibrium.
2OH-(aq) + 2H+(aq) <-> 2H2O
As a result, the concentration of OH- ions will decrease, causing the Mg(OH)2 to dissolve further to replenish the OH- ions that were consumed.
b) What would happen to the solubility of Mg(OH)2?
The solubility of Mg(OH)2 is directly related to the concentration of the dissolved ions in the solution. When acid is added, as explained in the previous step, the concentration of OH- ions decreases. This reduction in OH- concentration drives the equilibrium to the right, causing more Mg(OH)2 to dissolve. Therefore, the solubility of Mg(OH)2 will increase.
c) What would happen to the Ksp?
The Ksp, or the solubility product constant, is an equilibrium constant that is specific to a particular salt and represents the equilibrium expression for the dissociation of that salt. For the given equilibrium:
Mg(OH)2(aq) <-> Mg2+ (aq) + 2OH-(aq)
The Ksp expression can be written as:
Ksp = [Mg2+][OH-]^2
Since both [Mg2+] and [OH-] are involved in the equilibrium expression, and adding acid decreases the concentration of OH- ions, the Ksp value would remain the same. Adding acid does not directly affect the concentration of Mg2+ ions, so the Ksp value would remain unchanged.
In summary:
a) Adding acid would cause the equilibrium to shift to the right, consuming OH- ions and causing more Mg(OH)2 to dissolve.
b) The solubility of Mg(OH)2 would increase due to the decrease in OH- ion concentration.
c) The Ksp value would stay the same as it only depends on the concentration of the ions involved in the equilibrium expression.