Ethanol is a product of fermentation of simple sugars. Which method is used to separate ethanol from the other products?

Analyze the question: After fermentation, you get a mixture of ethanol, water, and other substances (such as yeast and other by-products). We need the method used to separate ethanol from this mixture.

Concept: Separation methods depend on the physical properties of the components:

• Filtration separates insoluble solids from liquids.
• Crystallisation separates dissolved solids from solutions.
• Fractional distillation separates miscible liquids with different boiling points.
• Isomerisation is a chemical rearrangement of a molecule into its isomer. It is not a separation method.

Solution:

1. The fermented mixture is mostly a liquid, with ethanol dissolved in water. Ethanol and water are miscible, so they cannot be separated by filtration.
2. Ethanol is a liquid, so crystallisation does not apply.
3. Ethanol boils at about 78°C, while water boils at 100°C. This difference allows separation by fractional distillation. The ethanol, being more volatile, vaporises first and is collected as the distillate.
4. Option A says "boiling off the ethanoic". Ethanoic acid is a different compound (acetic acid), and simple boiling off would not give a clean separation of ethanol.
5. Option E, isomerisation, is not a separation technique.

Answer: D, fractional distillation

Tip: When you see "separate two miscible liquids", think fractional distillation. Remember the examples: ethanol from water, and crude oil into its fractions. For "insoluble solid from liquid", think filtration.