Question

Magnesium hydroxide is only very slightly soluble in water. The reaction by which it goes into solution is:

Mg(OH)₂(s) ⇌ Mg²⁺(aq) + 2 OH⁻(aq)

What will happen if H⁺ is added to the solution and why?

Question options:

	Solid dissolves. OH- concentration increases. Reaction moves to the left.
	Solid dissolves. OH- concentration decreases. Reaction moves to the left.
	Solid dissolves. OH- concentration increases. Reaction moves to the right.
	Solid remains. OH- concentration increases. Reaction moves to the right.
	Solid remains. OH- concentration increases. Reaction moves to the left.
	Solid remains. OH- concentration decreases. Reaction moves to the right.
	Solid dissolves. OH- concentration decreases. Reaction moves to the right.
	Solid remains. OH- concentration decreases. Reaction moves to the left.

Answer 1

First, let us state the Le Chatelier principle which deals with changes in an equilibrium:

The statement is as follows:

If any equilibrium is disturbed, that is, change in conditions such as P,T, concentration, partial pressure, etc.., the system will counterbalance such change in order to favour the system's equilbirium.

• Change in concentration
• Change in pressure
• Change in temperature

In this specifric case, we are only changing OH- concentration

since H+ addition will neutralize OH- as follows

OH- + H+ = H2O

therefore

Mg(OH)2(s) ⇌ Mg2+(aq) + 2 OH−(aq)

shifts toward Mg+2 and OH- prodution, since OH- is dissapearing

the solid will becomes MORE soluble

therefore,

solid dissolves; OH- decreases, since Mg+2 ions are taking up for hte neutralization and the shift moves toward the right