(a) Name one gaseous hydrocarbon which is
(i) used for welding.
(ii) a major raw material for the plastic industry.
(b) Write the structural formula of the hydrocarbon in (a)(i) above. Name the process by which it can be converted to neoprene rubber.
(c) Potatoes contain a high proportion of carbohydrate.
(i) Give the main product formed when potatoes are dehydrated completely
(ii) Describe how you would convert potatoes to ethanol. State the reactions involved the process and write equation for the final stage of the conversion.
(iii) Draw a labelled diagram of the apparatus you would use to obtain a sample of fairly pure ethanol from the product formed in (c)(ii) above. What is the name given to the technique?
Explanation
(a)(i) Acetylene
(ii) Ethene
(b) The structural formula of acetylene (ethyne) is CH=CH. The process of converting acetylene to neoprene rubber is polymerization.
(i) The product of complete dehydration of potatoes is mainly starch.
(ii) the conversion of potatoes to ethanol involves the following process. Pressure cook the potatoes to release the starch granules. Treat the starch granules with malt and the malt supplies an enzyme called diastase which hydrolyse the starch to a sugar, maltose. At room temperature, yeast is then added which supplies the enzyme maltose that catalyse the hydrolysis of maltose to glucose. Finally, another enzyme of yeast, zymase, catalyses the decomposition of glucose to ethanol and carbon(IV) oxide.
i.e. \(C_6H_{12}O_{6(aq)} \to 2C_2H_5OH_{(aq)} + 2CO_{2(g)}\)
zymase
(iii) The technique is the distillation process. Give the diagram of the distillation