Potassium dichromate
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| Names | |
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IUPAC name
Potassium dichromate(VI)
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| Other names
potassium bichromate
bichromate of potash |
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| Identifiers | |
7778-50-9 
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| 3D model (Jmol) | Interactive image |
| ChEMBL | ChEMBL1374101 |
| ChemSpider |
22910
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| ECHA InfoCard | 100.029.005 |
| EC Number | 231-906-6 |
| PubChem | 24502 |
| RTECS number | HX7680000 |
| UN number | 3288 |
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| Properties | |
| K2Cr2O7 | |
| Molar mass | 294.185 g/mol |
| Appearance | red-orange crystalline solid |
| Odor | odorless |
| Density | 2.676 g/cm3, solid |
| Melting point | 398 °C (748 °F; 671 K) |
| Boiling point | 500 °C (932 °F; 773 K) decomposes |
| 4.9 g/100 mL (0 °C) 102 g/100 mL (100 °C) |
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| Solubility | insoluble in alcohol |
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Refractive index (nD)
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1.738 |
| Structure | |
| Triclinic (α-form, <241.6 °C) | |
| Tetrahedral (for Cr) | |
| Thermochemistry | |
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Std molar
entropy (S |
291.2 J K−1 mol−1 |
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Std enthalpy of
formation (ΔfH |
-2033 kJ/mol |
| Hazards | |
| Safety data sheet | ICSC 1371 |
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EU classification (DSD)
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Oxidant (O) Carc. Cat. 2 Muta. Cat. 2 Repr. Cat. 2 Highly toxic (T+) Harmful (Xn) Corrosive (C) Dangerous for the environment (N) |
| R-phrases | R45, R46, R60, R61, R8, R21, R25, R26, R34, R42/43, R48/23, R50/53 |
| S-phrases | S53, S45, S60, S61 |
| NFPA 704 | |
| Flash point | non-flammable |
| Lethal dose or concentration (LD, LC): | |
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LD50 (median dose)
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25 mg/kg (oral, rat) |
| Related compounds | |
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Other anions
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Potassium chromate Potassium molybdate Potassium tungstate |
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Other cations
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Ammonium dichromate Sodium dichromate |
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Related compounds
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Potassium permanganate |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 (what is  ?) |
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| Infobox references | |
bichromate of potash
dipotassium dichromate
dichromic acid, dipotassium salt
chromic acid, dipotassium salt
Potassium dichromate, K2Cr2O7, is a common inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is acutely and chronically harmful to health. It is a crystalline ionic solid with a very bright, red-orange color. The salt is popular in the laboratory because it is not deliquescent, in contrast to the more industrially relevant salt sodium dichromate.
Potassium dichromate is usually prepared by the reaction of potassium chloride on sodium dichromate. Alternatively, it can be obtained from potassium chromate by roasting chrome ore with potassium hydroxide. It is soluble in water and in the dissolution process it ionizes:
Potassium dichromate is an oxidising agent in organic chemistry, and is milder than potassium permanganate. It is used to oxidize alcohols. It converts primary alcohols into aldehydes and, under more forcing conditions, into carboxylic acids. In contrast, potassium permanganate tends to give carboxylic acids as the sole products. Secondary alcohols are converted into ketones. For example, menthone may be prepared by oxidation of menthol with acidified dichromate. Tertiary alcohols cannot be oxidized.
In an aqueous solution the color change exhibited can be used to test for distinguishing aldehydes from ketones. Aldehydes reduce dichromate from the +6 to the +3 oxidation state, changing color from orange to green. This color change arises because the aldehyde can be oxidized to the corresponding carboxylic acid. A ketone will show no such change because it cannot be oxidized further, and so the solution will remain orange.
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