Organic and inorganic compounds, and the oxides of carbon
Most carbon compounds are organic; carbonates, carbides, CO and CO₂ are inorganic. Carbon monoxide is poisonous, while carbon dioxide is used in soft drinks and as dry ice.
Organic and inorganic compounds
| Feature | Organic | Inorganic |
|---|---|---|
| Examples | Starch, petrol, ethanol, proteins | Marble, calcium carbide, carbon monoxide, hydrogen cyanide |
| Sources | Plants and animals, coal and petroleum, and laboratories | Mostly minerals |
| Melting point | Usually low-melting solids, or liquids | Usually solids with high melting and boiling points |
| Solubility | Usually dissolve in organic solvents (benzene, alcohol, chloroform), not in water | Usually dissolve in water, not in organic solvents |
| How many | A very large number, growing every day | Far fewer |
Carbon monoxide and carbon dioxide
| Feature | Carbon monoxide, CO | Carbon dioxide, CO₂ |
|---|---|---|
| Formed by | Burning carbon or hydrocarbons in limited oxygen: 2C + O₂ → 2CO | Burning in plenty of oxygen: C + O₂ → CO₂; CH₄ + 2O₂ → CO₂ + 2H₂O |
| Other sources | Exhaust of motor vehicles | Heating carbonates: CaCO₃ → CaO + CO₂; fermentation of sugar |
| Colour and smell | Colourless, odourless | Colourless, odourless |
| Low temperatures | Boils at about −192 °C | The solid (dry ice) sublimes at −78 °C |
| Effect | Poisonous: it binds with haemoglobin and cuts the oxygen carried by blood | A tiny part of the air; a main cause of the greenhouse effect |
| Nature | Neutral oxide | Acidic oxide |
Uses of carbon monoxide
- A reducing agent: in the blast furnace it takes oxygen from iron oxide: Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g).
- With hydrogen and a catalyst, it gives methanol, CH₃OH.
- It forms nickel carbonyl, Ni(CO)₄, which is used to purify nickel.
- It is used as a fuel and to make many organic compounds.
Uses of carbon dioxide
- Dry ice (solid CO₂) is a refrigerant. It sublimes at −78 °C, leaving no liquid behind.
- It gives the fizz in carbonated (soda) drinks.
- It is used to make washing soda and baking soda in the Solvay process.
- Fermentation of glucose gives ethanol and CO₂: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂.
Why carbon monoxide is dangerous
Carbon monoxide has no colour and no smell, so you cannot tell when it is present. A little causes headache and drowsiness; a lot can kill. It joins with haemoglobin, the red pigment of blood, so the blood carries less oxygen. Never burn a charcoal angithi or run a generator in a closed room, and keep vehicle engines well tuned.
In winter, people who sleep in a closed room with a burning angithi (coal or charcoal stove) can be poisoned by carbon monoxide. Always keep a window open. The fizz in a soda bottle is carbon dioxide dissolved under pressure.
2 marks: “A family sleeps in a closed room with a burning charcoal stove and wakes with headaches. Name the gas responsible and explain how it harms the body.” Carbon monoxide, formed when charcoal burns in limited air. It binds with haemoglobin and reduces the oxygen the blood can carry, causing headache, drowsiness or even death.
2 marks: “Give two differences between carbon monoxide and carbon dioxide.” Formation: CO forms in limited oxygen, CO₂ in plenty of oxygen. Nature: CO is neutral and poisonous; CO₂ is acidic, harmless in small amounts and used in soft drinks.
1 marks: “Name the solid form of carbon dioxide that is used as a refrigerant.” Dry ice.
Little oxygen gives CO (the killer); plenty of oxygen gives CO₂ (the fizz).