The functional group in the alcohols is the hydroxyl group, -OH. It is responsible for the typical reactions of alcohols. Take care not to confuse the -OH group with the hydroxide ion, OH - .

The alcohols form a homologous series . Like all homologous series, the alcohols:

The table shows four alcohols, their molecular formulae and their structures.

Making ethanol by fermentation

Ethanol is the alcohol found in beer, wine and other alcoholic drinks. It is also used as a fuel for vehicles, either on its own or mixed with petrol . Ethanol can be produced by fermentation and concentrated using fractional distillation .

Fermentation

Fermentation is an anaerobic process:

glucose → ethanol + carbon dioxide

Yeast , a type of single-celled fungus , provides the enzymes needed for fermentation. If the yeast cells become too cold, fermentation happens very slowly, or may not happen at all. If the yeast cells become too hot, their enzymes become denatured and fermentation stops.

The typical conditions needed for fermentation include:

sugars dissolved in water, and mixed with yeast

an air lock to allow carbon dioxide out, while stopping air getting in

warm temperature , 25-35°C

The yeast dies when the ethanol concentration reaches about 15%. Fermentation is a slow reaction and takes several days or weeks to finish. If air is present, the oxygen causes the ethanol to oxidise to ethanoic acid, so the drink tastes of vinegar.