Alcohols & Carboxylic AcidsEdexcel GCSE Chemistry: Revision notes

Alcohols are a homologous series with the functional group –OH. The four required members are:

Each molecule is a chain of carbon atoms fully covalently bonded to hydrogen atoms, with one carbon bonded to an –OH group instead of a hydrogen. You should be able to draw the full structure showing every covalent bond (all C–H, C–C and C–O and O–H bonds).

Alcohols can be dehydrated (have water removed) to form alkenes.

Core Practical: the temperature rise produced in a known mass of water is measured when burning each of ethanol, propanol, butanol and pentanol, to compare how much heat energy each releases.

Method outline:

1. Measure a known volume/mass of water into a container (e.g. a metal calorimeter)
2. Record the starting temperature of the water
3. Burn a measured mass of the alcohol in a spirit burner beneath the water, using the flame to heat the water
4. Record the highest temperature reached and calculate the temperature rise
5. Repeat for each alcohol, controlling variables (same volume of water, same starting temperature, similar burning time/distance)

A larger temperature rise indicates more heat energy released per gram of fuel burned. As the alcohols get larger (more carbon atoms), they generally release more energy per mole burned.

Carboxylic acids are a homologous series with the functional group –COOH. The four required members are:

You should be able to draw the full structures showing every covalent bond.

Solutions of carboxylic acids show typical acidic properties — e.g. they turn litmus red, react with metals to release hydrogen, and react with carbonates to release carbon dioxide — because they release H⁺ ions in solution.

Ethanol can be oxidised to produce ethanoic acid (this reaction happens when wine is left open to air and turns to vinegar). This same pattern extends to other alcohols: each alcohol can be oxidised to the carboxylic acid with the same number of carbon atoms (e.g. propanol → propanoic acid).

Fermentation: ethanol is produced industrially and traditionally by fermentation of carbohydrates (sugars) in aqueous solution, using yeast to provide the enzymes needed for the reaction. Fermentation is carried out at a warm temperature (around 25–35 °C) without oxygen (anaerobic conditions), because oxygen would allow the ethanol to be oxidised.

The fermentation mixture only contains a dilute solution of ethanol. To obtain a concentrated solution, the mixture is purified by fractional distillation, which separates the ethanol from water and other substances based on differing boiling points.

Members of a given homologous series (e.g. all alcohols, or all carboxylic acids) have similar chemical reactions because their molecules all contain the same functional group. This lets you predict the products of a reaction for a member of the series you haven't specifically been taught, as long as you know its functional group and the general reaction pattern.

For example, since ethanol is oxidised to ethanoic acid, you can predict that propan-1-ol will be oxidised to propanoic acid, following the same pattern.