Chromium(III) oxide
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_oxide.jpg) OTC Cr2O3 sold as pigment. It is impure and indurated.
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| Names | |
|---|---|
| IUPAC name
Chromium(III) oxide
| |
| Other names
Chrome green
Chromia Chromium sesquioxide Dichromium trioxide Eskolaite | |
| Properties | |
| Cr2O3 | |
| Molar mass | 151.9904 g/mol |
| Appearance | Green solid |
| Odor | Odorless |
| Density | 5.22 g/cm3 |
| Melting point | 2,435 °C (4,415 °F; 2,708 K) |
| Boiling point | 4,000 °C (7,230 °F; 4,270 K) |
| 3·10-5 g/100 ml (20 °C) | |
| Solubility | Reacts with strong acids, molten alkali Insoluble in alcohol, ethers, ketones |
| Vapor pressure | ~0 mmHg |
| Thermochemistry | |
| Std molar
entropy (S |
81 J·mol−1·K−1 |
| Std enthalpy of
formation (ΔfH |
−1128 kJ/mol |
| Hazards | |
| Safety data sheet | Sigma-Aldrich |
| Flash point | Non-flammable |
| Related compounds | |
| Related compounds
|
Chromium trioxide |
| Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
| Infobox references | |
Chromium(III) oxide, also known as chrome green, chromia, or chromium sesquioxide is the inorganic compound with chemical formula Cr2O3.
Contents
Properties
Chemical
Chromium(III) oxide reacts with acids to form chromium(III) salts, though samples that have been heavily annealed at high temperature, such as commercial varieties, are not readily attacked by acids or bases. Molten alkalis react with chromium(III) oxide to form chromates or chromites. Molten potassium nitrate reacts with it to form potassium dichromate, though indurated chromia reacts very slowly. Chromium(III) oxide can be used to produce a low-energy thermite with aluminum or magnesium powder, which is difficult to ignite. It can catalyze the oxidation of ammonia to nitric oxide when heated to red heat and put into a flask of ammonia gas.
Physical
Chromium(III) oxide is a dark green powder and is slightly hygroscopic. It turns brown when heated, but reverts to its dark green color when cooled.
Availability
Chrome green is available at pottery shops as a green pigment, sometimes with traces of calcium carbonate. This material, however, is generally too unreactive to produce other chromium compounds.
Purer chromium(III) oxide can be purchased from chemical suppliers.
Preparation
Chromium(III) oxide can be prepared by reducing potassium dichromate with sulfur:
- K2Cr2O7 + S → K2SO4 + Cr2O3
It can also be prepared from the thermal decomposition of ammonium dichromate:
- (NH4)2Cr2O7 → Cr2O3 + N2 + 4 H2O
or by reacting chromium trioxide with ethanol.
It is the most common byproduct of the reduction of chromium(VI) compounds, especially in neutral solution.
Projects
- Make chromium metal
- Make sodium chromate
- Make potassium dichromate
Handling
Safety
Chromium(III) oxide is not extremely reactive. If ingested it may cause nausea, vomiting and diarrhea. As it stains, gloves and protective clothing should be worn.
Storage
Chromia doesn't require any special storage. Can be kept in any clean bottle.
Disposal
While not as toxic as chromium(VI) compounds, it's best to avoid dumping it in the environment.
