A fermentation mixture is fractionally distilled. Ethanol boils at 78 ∘C^\circ\mathrm{C}∘C and water boils at 100 ∘C^\circ\mathrm{C}∘C. The liquid collected at about 78 ∘C^\circ\mathrm{C}∘C is much richer in ethanol than the mixture in the flask.
Which statement best explains this?
Ethanol molecules are lighter than water molecules, so ethanol vapour rises further up the column
Water vapour condenses more readily in the cooler column and runs back, while ethanol vapour passes on
Water does not evaporate until the mixture reaches 100 ∘C^\circ\mathrm{C}∘C, so only ethanol enters the column
The column is hottest at the top, so only the liquid with the lower boiling point stays as a vapour there
43 exam-style questions on Edexcel GCSE Chemistry 10.4 Alcohols and carboxylic acids, covering 10.4.1 Alcohols and the -OH functional group, 10.4.2 Carboxylic acids and the -COOH functional group, 10.4.3 Oxidation of alcohols and homologous series, and 10.4.4 Fermentation and fractional distillation of ethanol. Each one has a worked solution and a mark scheme showing where the marks go.