O₂
Compound · Gas
Oxygen
氧气
Oxygen (氧气), formula O₂, is a gas with a molar mass of 32 g/mol (CAS 7782-44-7). Colourless odourless gas; pale blue when liquid; slightly soluble in water (sustains aquatic life).
Key facts
| Molar mass | 32 g/mol |
|---|---|
| Category | Gas |
| State at 25°C | Gas |
| CAS | 7782-44-7 |
Structure
O=O
Diatomic non-polar molecule; supports combustion
Physical properties
| Appearance | Colourless odourless gas; pale blue when liquid |
|---|---|
| Melting point | −219 °C |
| Boiling point | −183 °C |
| Density | 1.43 g/L (气体) |
| Solubility | Slightly soluble in water (sustains aquatic life) |
Key reactions
C + O₂ →(点燃) CO₂
Supports combustion of carbon
3Fe + 2O₂ →(点燃) Fe₃O₄
Iron burns vigorously in oxygen
2H₂ + O₂ →(点燃) 2H₂O
Combines with hydrogen to form water
Main uses
- Medical oxygen and life support
- Steelmaking and oxy-fuel welding/cutting
- Aeration in wastewater treatment
Hazard
LowNon-flammable itself but strongly supports fire; high-pressure or oxygen-rich settings are a fire risk
Constituent elements
Data sources
Molar mass is computed from IUPAC (CIAAW) standard atomic weights; formula, properties and reactions can be verified on PubChem, NIST and Wikipedia. The CAS number is the substance's unique registry identifier. Educational reference only.