Describe the manufacture of ethanol from molasses. Give any two chemical properties of ethanol with equations.

How to lay out the answer. Follow the frame, then write it in your own words.

1 · Open in one line. Ethanol (C₂H₅OH) is made in industry by the fermentation of molasses using yeast.
2 · Prepare the molasses.
- Dilute it to 8 to 10% sugar.
- Add ammonium sulphate or ammonium phosphate as food for yeast, if needed.
- Add yeast; keep at about 303 K for a few days.
3 · Write the two enzyme equations.
- C₁₂H₂₂O₁₁ + H₂O → C₆H₁₂O₆ + C₆H₁₂O₆ (invertase)
- C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (zymase)
4 · Draw a flow chart. [Molasses → dilution → yeast, 303 K → wash → fractional distillation → rectified spirit (95.5%) → quicklime, reflux → absolute alcohol (100%)]
5 · Two chemical properties.
- With sodium: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑
- Dehydration: C₂H₅OH → C₂H₄ + H₂O (excess conc. H₂SO₄, 443 K)
6 · Real life. Indian sugar mills make ethanol from molasses for sanitisers and for blending with petrol.
7 · Close in one line. Thus a by-product of the sugar industry becomes a useful fuel and solvent.

Scoring tip: Write both enzyme equations with the enzyme names over the arrows. The conditions (303 K, 443 K, 573 K) earn marks, so learn them.