Alcohols as a homologous series, the functional group, and the production of ethanol by fermentation and by hydration of ethene.

A topic 2.5 structured question. Sugar (glucose) is dissolved in water and yeast is added (1 mark). The mixture is kept warm (about $30\,^{\circ}\text{C}$) and without air (anaerobic) conditions (1 mark). Enzymes in the yeast convert the sugar into ethanol and carbon dioxide (1 mark). Word equation: glucose $\rightarrow$ ethanol + carbon dioxide (1 mark). Markers reward yeast, the warm anaerobic conditions, and the correct word equation. A common error is to forget that air must be kept out, or to set the temperature too high so the enzymes denature.

A topic 2.5 compare question. The hydration of ethene with steam (using a catalyst) is a continuous process that is fast and makes pure ethanol, but uses crude oil (a finite resource) and high temperatures and pressures (1 mark). Fermentation uses a renewable raw material (sugar from plants) and gentle conditions, but is slow, a batch process, and gives a dilute product that must be distilled (1 mark). So hydration is faster and gives purer ethanol, while fermentation uses renewable resources (1 mark). Markers reward a valid point for each method and a comparison. A common error is to list features without comparing.