(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 ...
Question 1 Report
(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?
Answer Details
(a) Gaseous hydrocarbons
- (i) Used for welding: ethyne (acetylene), C2H2 (its oxy-acetylene flame is very hot).
- (ii) Major raw material for the plastic industry: ethene (ethylene), C2H4.
(b) Structural formula and process
Structural formula of ethyne: \[H-C \equiv C-H\] Ethyne is converted to neoprene rubber by polymerization (the monomer chloroprene, made from ethyne, polymerizes to neoprene).
(c) Potatoes
- (i) On complete dehydration of the carbohydrate (starch), the main product is carbon (with water driven off).
- (ii) Converting potatoes to ethanol:
First, the starch is hydrolysed. Boiling the mashed potato with dilute acid, or using the enzyme diastase, breaks starch down to maltose, and maltase converts maltose to glucose: \[(C_6H_{10}O_5)_n + nH_2O \rightarrow n C_6H_{12}O_6\] Then the glucose is fermented by the enzyme zymase in yeast at about 30 to 35 °C: \[C_6H_{12}O_6 \xrightarrow{zymase} 2C_2H_5OH + 2CO_2\] - (iii) A fairly pure sample of ethanol is obtained from the fermented mixture by fractional distillation (see diagram note). The technique is called fractional distillation.
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