dichromate

Dichromate refers to the dichromate ion, Cr2O7^2-, and to salts containing this group. The ion comprises two chromate units linked by an oxygen bridge, with two chromium atoms in the +6 oxidation state and seven oxygens in total. Dichromate salts, such as potassium dichromate K2Cr2O7 and sodium dichromate Na2Cr2O7, are typically bright orange crystalline solids. In aqueous solution, the relative amounts of chromate (CrO4^2-) and dichromate depend on pH: acidic conditions shift equilibrium toward Cr2O7^2-, while basic conditions favor CrO4^2-.

Industrial and laboratory context: Dichromate salts are common oxidants and reagents in inorganic and organic chemistry. They are prepared by acidifying chromate solutions and crystallizing the dichromate salt; they are soluble in water, forming orange solutions that are used in redox titrations and qualitative analysis.

Uses and reactions: In acidic media, dichromate is a strong oxidizing agent and is reduced to Cr3+. It has historically been used for oxidation of alcohols, in dyeing and leather processing, and as a gelatin hardener in photography. It remains used in some textile and wood-processing applications, and in analytical chemistry as a standard oxidant and in redox reactions.

Safety and environmental notes: Chromium(VI) compounds, including dichromate, are toxic and carcinogenic to humans and hazardous to the environment. They cause irritation and require careful handling with gloves, eye protection, and proper waste disposal. Dichromate solutions should be kept away from acids and reducing agents and stored in closed containers away from incompatibles.