Dichromate ion (Cr₂O₇²⁻)
- Charge
- −2
- Atoms
- Cr × 2, O × 7
- Atoms in total
- 9
- Mass of the ion
- 215.985 g/mol
Dichromate is two chromium atoms linked through a shared oxygen atom, with seven oxygen atoms in all and a 2− charge. Each chromium is in the +6 state, so 2(+6) + 7(−2) = −2. Its orange solutions are strong oxidizing agents used in titrations and in the early breath-alcohol tubes that turned green when alcohol was present.
- The prefix di- shows two chromium atoms; dichromate forms from two chromate ions in acid and turns back into yellow chromate in base.
- When dichromate oxidizes something, chromium drops from +6 to +3 and the color changes from orange to green.
- Potassium dichromate, K₂Cr₂O₇, is the most common dichromate salt, and like other chromium(VI) compounds it is toxic and causes cancer.