CO₂
Compound · Oxide
Carbon dioxide
二氧化碳
Carbon dioxide (二氧化碳), formula CO₂, is a oxide with a molar mass of 44.01 g/mol (CAS 124-38-9). Colourless odourless gas; solid form is dry ice (sublimes); dissolves in water to form carbonic acid.
Key facts
| Molar mass | 44.01 g/mol |
|---|---|
| Category | Oxide |
| State at 25°C | Gas |
| CAS | 124-38-9 |
Structure
O=C=O
Linear, non-polar molecule
Physical properties
| Appearance | Colourless odourless gas; solid form is dry ice (sublimes) |
|---|---|
| Melting point | −78.5 °C (升华) |
| Boiling point | — |
| Density | 1.98 g/L (气体) |
| Solubility | Dissolves in water to form carbonic acid |
Key reactions
CO₂ + H₂O ⇌ H₂CO₃
Dissolves in water as carbonic acid
CO₂ + Ca(OH)₂ → CaCO₃↓ + H₂O
Turns limewater milky — the CO₂ test
6CO₂ + 6H₂O →(光照) C₆H₁₂O₆ + 6O₂
Photosynthesis fixes carbon
Main uses
- Carbonating beverages
- Dry-ice refrigeration and stage fog
- Fire suppressant and greenhouse enrichment
Hazard
LowNon-toxic, but high concentrations cause asphyxiation
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.