Write the net ionic equation for the reaction that takes place between aqueous magnesium chloride and aqueous sodium hydroxide: MgCl2(aq) + 2NaOH(aq) → Mg(OH)2(s) + 2NaCl(aq)
The Correct Answer and Explanation is:
Net Ionic Equation:
Mg2+(aq)+2OH−(aq)→Mg(OH)2(s)\text{Mg}^{2+}(aq) + 2\text{OH}^-(aq) \rightarrow \text{Mg(OH)}_2(s)Mg2+(aq)+2OH−(aq)→Mg(OH)2(s)
Explanation:
To write the net ionic equation, we start by understanding what occurs in the reaction between magnesium chloride and sodium hydroxide in aqueous solution.
The full balanced molecular equation is:
MgCl2(aq)+2NaOH(aq)→Mg(OH)2(s)+2NaCl(aq)\text{MgCl}_2(aq) + 2\text{NaOH}(aq) \rightarrow \text{Mg(OH)}_2(s) + 2\text{NaCl}(aq)MgCl2(aq)+2NaOH(aq)→Mg(OH)2(s)+2NaCl(aq)
Both magnesium chloride (MgCl₂) and sodium hydroxide (NaOH) are soluble in water and dissociate completely into their ions:
- Magnesium chloride dissociates into one magnesium ion (Mg²⁺) and two chloride ions (Cl⁻).
- Sodium hydroxide dissociates into sodium ions (Na⁺) and hydroxide ions (OH⁻).
This gives us the full ionic equation:
Mg2+(aq)+2Cl−(aq)+2Na+(aq)+2OH−(aq)→Mg(OH)2(s)+2Na+(aq)+2Cl−(aq)\text{Mg}^{2+}(aq) + 2\text{Cl}^-(aq) + 2\text{Na}^+(aq) + 2\text{OH}^-(aq) \rightarrow \text{Mg(OH)}_2(s) + 2\text{Na}^+(aq) + 2\text{Cl}^-(aq)Mg2+(aq)+2Cl−(aq)+2Na+(aq)+2OH−(aq)→Mg(OH)2(s)+2Na+(aq)+2Cl−(aq)
Next, we eliminate the spectator ions, which are the ions that appear unchanged on both sides of the equation. In this case, sodium (Na⁺) and chloride (Cl⁻) ions are spectator ions.
What remains is the net ionic equation:
Mg2+(aq)+2OH−(aq)→Mg(OH)2(s)\text{Mg}^{2+}(aq) + 2\text{OH}^-(aq) \rightarrow \text{Mg(OH)}_2(s)Mg2+(aq)+2OH−(aq)→Mg(OH)2(s)
This equation shows that when aqueous magnesium ions react with hydroxide ions, an insoluble compound called magnesium hydroxide (Mg(OH)₂) forms as a solid precipitate. This is a typical double displacement reaction that results in the formation of a precipitate, which is why it is classified as a precipitation reaction. The reaction helps illustrate how insoluble compounds can be formed from soluble ionic reactants.
