(a) Define each of the following terms: I. biotechnology; II. biogas.
(b) (i) Describe briefly the production of ethanol from sugar cane juice.
(iii) Mention two uses of the by-product.
(iv) Ethanol can be produced from both cane sugar and petroleum. Explain briefly why the ethanol from cane sugar is renewable but that from petroleum is non-renewable.
(c) Distinguish between heavy chemicals and fine chemicals. Give one example of each chemical.
(d) Arrange the following gases in increasing order of deviation from ideal gas behaviour: HCl; O\(_2\); Cl\(_2\). Give reason(s) for your answer.
(a)(i) I. Biotechnology: the use of living organisms (or their components, such as enzymes or micro-organisms) to make useful products or to carry out useful processes for man. II. Biogas: a mixture of gases (mainly methane and carbon(IV) oxide) produced by the anaerobic bacterial decomposition of organic matter, used as a fuel.
(a)(ii) Applications of biotechnology: production of alcoholic drinks/ethanol by fermentation; production of antibiotics and drugs; production of biogas; making of bread, yoghurt and cheese (any two).
(b)(i) Ethanol from sugar cane juice: the sugar cane juice, which contains sucrose, is diluted and yeast is added. The enzyme invertase (sucrase) in yeast hydrolyses sucrose to glucose and fructose, then zymase ferments these sugars to ethanol at about 30-40 °C in the absence of air:
\[ \text{C}_6\text{H}_{12}\text{O}_6 \xrightarrow{\text{zymase}} 2\text{C}_2\text{H}_5\text{OH} + 2\text{CO}_2 \]
The ethanol is then concentrated by fractional distillation.
(b)(ii) By-product: carbon(IV) oxide (CO2).
(b)(iii) Uses of the by-product: making fizzy (carbonated) drinks; used as a fire extinguisher; solid CO2 (dry ice) as a refrigerant.
(b)(iv) Ethanol from cane sugar is renewable because sugar cane is a crop that can be replanted and regrown within a short time, so the source is continuously replaceable. Ethanol from petroleum is non-renewable because petroleum is a fossil fuel formed over millions of years and cannot be replaced once used up.
(c) Heavy vs fine chemicals: heavy chemicals are produced in very large quantities, are relatively cheap and impure, e.g. tetraoxosulphate(VI) acid (H2SO4) or sodium trioxocarbonate(IV). Fine chemicals are produced in small quantities, are of high purity and are expensive, e.g. drugs/pharmaceuticals or dyes.
(d) Increasing order of deviation from ideal behaviour: O2 < Cl2 < HCl. Reason: deviation from ideal behaviour increases with the strength of intermolecular forces and with molecular size/polarity. O2 is small and non-polar (least deviation); Cl2 is larger and more polarisable; HCl is polar with strong dipole-dipole attractions, so it deviates most.
