GCSE Chemistry · AQA 8462 · Topic 4.7.2
Reactions of alkenes and alcohols
Key points
- Alkenes are hydrocarbons with a C=C double bond, general formula . They are unsaturated. Examples: ethene, propene, butene, pentene.
- Alkenes react by addition across the double bond: with hydrogen (with a catalyst) to make alkanes, with water (steam, catalyst) to make alcohols, and with halogens.
- Alcohols contain the –OH group: methanol, ethanol, propanol, butanol. They burn, dissolve in water to give neutral solutions, react with sodium to give hydrogen, and are oxidised to carboxylic acids.
- Ethanol is made by fermentation of sugar solutions with yeast at about 30 °C; it is used in drinks, as a fuel and as a solvent.
- Carboxylic acids contain –COOH: methanoic, ethanoic, propanoic, butanoic acid. They are weak acids and react with carbonates to give carbon dioxide.
- A carboxylic acid reacts with an alcohol (acid catalyst) to make an ester, e.g. ethyl ethanoate, which is volatile and has a fruity smell.
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Alkenes, alcohols and carboxylic acids are three homologous series, each defined by its functional group. Learn the first four members of each, their typical reactions, and how an alcohol and a carboxylic acid make an ester.
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