Alcohols
The alcohols
are a homologous series whose functional group is –OH (a hydroxyl group). Their names end in -ol.
| Alcohol | Formula |
|---|---|
| Methanol | CH₃OH |
| Ethanol | C₂H₅OH |
| Propanol | C₃H₇OH |
| Butanol | C₄H₉OH |
Alcohols are used as fuels and solvents. Ethanol is the alcohol in alcoholic drinks.
Key terms
Reactions of alcohols
- With sodium: they fizz, giving off hydrogen:
2Na + 2C₂H₅OH → 2C₂H₅ONa + H₂
- Burning in air: they burn completely to make , which is why they make good fuels:
C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
- In water: methanol, ethanol and propanol dissolve to form a neutral solution.
- they are oxidised to , either by an oxidising agent or by microbes in the air. Ethanol becomes , which is why opened wine turns to vinegar.
Key terms
Fermentation
Ethanol can be made by sugar (glucose) with :
glucose → ethanol + carbon dioxide
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
Conditions:
- a warm temperature, about 25–35 °C. Too cold and it is very slow; too hot and the yeast's and fermentation stops.
- no oxygen (anaerobic). If air gets in, the ethanol is oxidised to ethanoic acid.
- sugar dissolved in water
The carbon dioxide escapes through an air lock, which stops air getting in.