CO2
Carbon dioxide (CO2)
Also known as: carbonic acid gas
Carbon dioxide is a colourless gas produced by respiration, combustion and fermentation, and consumed by photosynthesis. The molecule is linear — O=C=O — and nonpolar overall. Dissolved in water it forms weak carbonic acid, which is why soda water tastes faintly sharp and why rising atmospheric CO₂ slowly acidifies the oceans.
Molar mass breakdown
44.009 g/mol| Element | Atoms | Mass (g/mol) | % by mass |
|---|---|---|---|
| Oxygen (O) | 2 | 31.998 | 72.71% |
| Carbon (C) | 1 | 12.011 | 27.29% |
What carbon dioxide is used for
- Carbonating drinks
- Fire extinguishers (denser than air, smothers flames)
- Dry ice for cooling and stage fog
- Photosynthesis — the carbon source for nearly all life
Key facts
- Molar mass ≈ 44.01 g/mol, denser than air — CO₂ pools in low places.
- Solid CO₂ (dry ice) sublimes directly from solid to gas at −78.5 °C.
- About 0.04% of the atmosphere, up from 0.03% a century ago — the main driver of recent climate change.
Frequently asked questions
What is the molar mass of CO2?
About 44.01 g/mol: 12.011 (C) + 2 × 15.999 (O).
Is CO2 poisonous?
It is not toxic like carbon monoxide, but at high concentrations it displaces oxygen and disrupts breathing — ventilation matters in enclosed spaces.
Why is CO2 nonpolar when its bonds are polar?
The molecule is perfectly linear, so the two polar C=O bonds pull in exactly opposite directions and cancel.