Overview

Potassium dichromate is a crystalline inorganic salt with the formula K2Cr2O7. It contains potassium cations and dichromate anions; the chromium in the compound is in the +6 oxidation state, commonly written as Cr(VI) and linked to strong oxidizing behavior. As an orange‑red solid, it is readily recognized by its distinctive color and tendency to yield green chromium(III) products on reduction.

Characteristics and chemical behavior

The compound is moderately soluble in water and forms acidic aqueous solutions. In solution equilibrium with the chromate ion governs color and speciation: acidic media favor dichromate, while alkaline media shift the balance toward chromate. As an oxidizing agent it accepts electrons from a range of organic and inorganic substrates and is used to convert alcohols to carbonyl compounds in classical organic procedures. Reduction of Cr(VI) to Cr(III) changes the appearance from orange to green or blue‑green.

Uses and examples

  • Laboratory oxidant: used in classical oxidation reactions and in preparation of chromium(VI) reagents for qualitative and quantitative analysis.
  • Analytical chemistry: historically used in certain titrations and standards and as a reagent in spot tests.
  • Industrial and historical applications: pigments, leather tanning, and photographic processing in the past; many of these uses have declined because of health and environmental concerns.

Hazards, regulation and handling

Chromium(VI) compounds, including potassium dichromate, are toxic and classified as carcinogenic and corrosive. They can cause severe skin irritation, ulceration, respiratory harm if inhaled, and long‑term health risks on chronic exposure. Because of these dangers, many jurisdictions tightly regulate manufacture, sale, and disposal. Safe handling requires personal protective equipment, fumehood use, and procedures to avoid dust and skin contact.

Disposal and environmental notes

End‑of‑life management normally involves chemical reduction of Cr(VI) to the less mobile and less toxic Cr(III), followed by precipitation and secure disposal under applicable regulations. Environmental contamination with hexavalent chromium has prompted remediation efforts and replacement of dichromate by safer alternatives in many applications.

Distinctions and historical context

Potassium dichromate should be distinguished from potassium chromate and from trivalent chromium salts. The dichromate/chromate equilibrium, controlled by pH, is a fundamental concept often demonstrated in teaching laboratories. Over the 20th century dichromate played a prominent role in industry and analytic chemistry; however, use has fallen because of the recognized toxicology of Cr(VI) and the availability of more benign reagents.

For introductory references and safety data see supplier and regulatory guidance: safety data, method summaries at standard references, and regulatory pages at government agencies and professional bodies.