1. Write the balanced molecular equation:
Al(OH)₃(s) + 3NaOH(aq) → Na₃Al(OH)₆(aq)
2. Write the complete ionic equation:
Al(OH)₃(s) + 3Na⁺(aq) + 3OH⁻(aq) → 3Na⁺(aq) + [Al(OH)₆]³⁻(aq)
3. Identify and cancel spectator ions:
Spectator ions are those that appear on both sides of the equation unchanged. In this case, the spectator ion is Na⁺.
4. Write the net ionic equation:
Al(OH)₃(s) + 3OH⁻(aq) → [Al(OH)₆]³⁻(aq)
Explanation:
* Aluminum hydroxide (Al(OH)₃) is a solid, so it doesn't break apart into ions.
* Sodium hydroxide (NaOH) is a strong base that dissociates completely in solution, forming Na⁺ and OH⁻ ions.
* Sodium aluminate (Na₃Al(OH)₆) is a complex ion that exists in solution.
The net ionic equation shows that aluminum hydroxide reacts with hydroxide ions to form the tetrahydroxoaluminate(III) complex ion, [Al(OH)₆]³⁻.
Key Points:
* Excess NaOH: The reaction requires excess NaOH to drive the formation of the complex ion.
* Amphoteric Nature: Aluminum hydroxide is amphoteric, meaning it can react with both acids and bases. In this case, it's acting as an acid, accepting hydroxide ions.
* Complex Ion Formation: The reaction forms a complex ion, which is a species containing a central metal ion surrounded by ligands (in this case, hydroxide ions).
