Chromate-Dichromate Equilibrium
2CrO42− + 2H+ ⇌ Cr2O72− + H2O
Overview
Chromate (yellow, CrO₄²⁻) converts to dichromate (orange, Cr₂O₇²⁻) in acidic solution and vice versa in basic solution. This pH-dependent equilibrium involves condensation of two tetrahedral chromate units. While chromium remains at +6 throughout, this equilibrium is fundamental to Cr(VI) redox chemistry.
Participants
| Role | Substance | Coefficient | State |
|---|---|---|---|
| Product | Water H₂O | 1 | (l) |
Everyday Example
Adding acid to yellow potassium chromate solution turns it orange, and adding base reverses it, demonstrating Le Chatelier's principle.
Industrial Importance
Chromate/dichromate equilibrium is important in chrome plating, leather tanning, and in understanding Cr(VI) environmental contamination.
Properties
- Type
- Redox
- Reversible
- Yes
- Energy
- Exothermic
- ΔH
- -14.0 kJ/mol
Related Reactions
Aqua Regia Dissolving Gold
Bleaching with Sodium Hypochlorite
Cerium(IV) Reduction by Iron(II)
Chlorine Oxidation of Bromide
Contact Process SO₂ Oxidation
Copper Displaced by Iron
Copper Oxidation by Nitric Acid
Copper Patina Formation (Verdigris)
Copper Reduction of Silver Ion
Dichromate Oxidation of Ethanol
Frequently Asked Questions
What is the equation for Chromate-Dichromate Equilibrium?
The balanced equation is: 2CrO₄²⁻ + 2H⁺ ⇌ Cr₂O₇²⁻ + H₂O.
What type of reaction is Chromate-Dichromate Equilibrium?
Chromate-Dichromate Equilibrium is a redox reaction. It is reversible under certain conditions.
Is Chromate-Dichromate Equilibrium exothermic or endothermic?
Chromate-Dichromate Equilibrium is exothermic (releases energy). The enthalpy change (ΔH) is -14.0 kJ/mol.