1. The Reaction
Crystal violet is a triarylmethane dye with the formula (C₂₅H₃₀N₃Cl). It reacts with hydroxide ions (OH⁻) to form a colorless product.
2. Complete Ionic Equation
* Crystal violet: (C₂₅H₃₀N₃Cl) (This is a complex ion, so we treat it as one unit)
* Sodium hydroxide: Na⁺(aq) + OH⁻(aq)
The complete ionic equation is:
(C₂₅H₃₀N₃Cl)(aq) + Na⁺(aq) + OH⁻(aq) → (C₂₅H₃₀N₃)(aq) + Cl⁻(aq) + Na⁺(aq) + H₂O(l)
3. Identify Spectator Ions
Spectator ions are ions that appear on both sides of the equation and do not participate in the reaction. In this case, the spectator ion is Na⁺.
4. Net Ionic Equation
Remove the spectator ion from the complete ionic equation to get the net ionic equation:
(C₂₅H₃₀N₃Cl)(aq) + OH⁻(aq) → (C₂₅H₃₀N₃)(aq) + Cl⁻(aq) + H₂O(l)
Key Points
* The reaction is a color change reaction. Crystal violet is a deep purple color, but the product is colorless, resulting in a decolorization.
* The reaction is an example of a base-catalyzed nucleophilic aromatic substitution. The hydroxide ion acts as a nucleophile, attacking the positively charged carbon atom in the crystal violet molecule.
