chromatedichromate

ChromateDichromate refers to the chromate-dichromate system in aqueous chromium(VI) chemistry, describing the two oxyanions CrO4^2- and Cr2O7^2-. Both species contain chromium in the +6 oxidation state and are interconvertible through protonation and dehydration.

The interconversion is governed by pH. In acidic solutions, dichromate (Cr2O7^2-) is favored; in basic or neutral solutions, chromate (CrO4^2-) predominates. The equilibrium can be represented approximately as Cr2O7^2- + H2O ⇌ 2 CrO4^2- + 2 H+. The exact distribution of species depends on total chromium and the solution’s pH. The two forms differ visually: dichromate is typically orange, while chromate is yellow, so mixtures may appear yellow, orange, or a blend depending on their relative concentrations.

ChromateDichromate solutions are commonly encountered in laboratory redox chemistry. Potassium dichromate, a widely used oxidizing agent in acidic media, can be reduced to Cr(III), causing a color change from orange to green that aids in monitoring reactions. The chromate form also participates in redox processes and can serve as a mild oxidant under appropriate conditions. Beyond reactions, the chromate-dichromate balance influences qualitative analysis and pigment chemistry, where color differences provide practical cues about acidity and speciation.

Safety and handling are important: chromium(VI) compounds are toxic and carcinogenic, and both chromate and dichromate are strong oxidizers. They should be used with appropriate PPE, in well-ventilated areas, and disposed of according to local regulations.