Burning magnesium will continue to burn in carbon dioxide, but the gas does not support combustion of most other substances. Carbon dioxide readily dissolves in water to form acidic solutions and it makes rain water naturally slightly acidic. 'Dry ice', which is often used to create fog in rock concerts and stage plays, is solid carbon dioxide.
| Symbol: | CO2 |
| Relative molecular mass: | 44 |
| Boiling point: | -78,15 °C |
| Key properties: | Unreactive gas. Solid and liquid carbon dioxide are very cold. |
| Some major uses: | Freezing food, fire extinguishers, fizzy drinks, keyhole surgery and medical breathing mixtures. |
| Discoverer: | Joseph Black (1752) |
In the air
Carbon dioxide forms just 0.038% of the air. It is a 'greenhouse gas' that absorbs heat energy in the atmosphere. The atmospheric concentration of carbon dioxide is increasing as a result of burning fossils fuels and deforestation. This contributes to global warming. Industrial amounts of carbon dioxide may be obtained by purifying the waste gases from combustion, fermentation or ammonia manufacture.
Liquid and solid
Carbon dioxide liquefies when cooled and pressurised to at least 520 kPa. For example, it will liquefy at 19,85 °C under a pressure of 3,000 kPa. Solid carbon dioxide or 'dry ice' forms when liquid carbon dioxide is allowed to return to normal atmospheric pressure. Dry ice sublimes (turns directly from solid to gas) at -78,15 °C.