* Equilibrium and Le Chatelier's Principle: Magnesium hydroxide is a slightly soluble compound, meaning it exists in equilibrium with its ions in solution:
Mg(OH)₂(s) ⇌ Mg²⁺(aq) + 2OH⁻(aq)
* Ammonium Chloride's Role: Ammonium chloride is a strong electrolyte that dissociates completely in solution:
NH₄Cl(aq) → NH₄⁺(aq) + Cl⁻(aq)
The ammonium ions (NH₄⁺) react with the hydroxide ions (OH⁻) from the magnesium hydroxide equilibrium:
NH₄⁺(aq) + OH⁻(aq) ⇌ NH₃(aq) + H₂O(l)
This reaction removes hydroxide ions from the solution, shifting the equilibrium of the magnesium hydroxide dissolution to the right, favoring the dissolution of more magnesium hydroxide.
In summary:
1. Adding NH₄Cl increases the concentration of NH₄⁺ ions.
2. These ions react with OH⁻ ions from the magnesium hydroxide equilibrium.
3. This reaction removes OH⁻ ions, causing the equilibrium to shift to the right, favoring the dissolution of more Mg(OH)₂.
Result: The overall effect is that more magnesium hydroxide dissolves in the presence of ammonium chloride.
