CHAPTER 11
Occurrence and extraction of metals
1. B
2. D
3. A
4. C
5. A
6. C
7. B
8. C
9. A
10. B
11. A
12. C
13. D
14. B
15. D
16. D
17. B
18. D
19. B
20. A
21. D
22. (1) Overhead power cables: very good conductor of electricity, low density, ductile
(2) Saucepans: very good conductor of heat, non-poisonous, malleable, corrosion resistant
(3) Soft drink cans: non-poisonous, light, corrosion resistant, malleable
(4) Window frames: corrosion resistant, strong
(Other answers may be given)
23. (a) Strong, malleable, ductile, corrosion resistant, non-poisonous.
(b) (i) No. When used to transmit wave or digital signals, optical fibres can replace copper wires. However, optical fibres are non-conductors of electricity. They therefore cannot replace copper wires to transfer electric current.
(ii) Aluminium could be used as a cheap substitute for copper in making electrical wires. However, electrical conductivity of aluminium is not as good as copper.
(c) The government may be reluctant to make more 'copper' coins. Besides, people may keep copper coins instead of spending them.
24. (a)
(b) The black mixture first heated to red hot, and finally changed into a reddish-brown solid.
(c) 2CuO(s) + C(s) ® 2Cu(s) + CO2(g)
(d) Oxygen in air would react with hot copper to form copper(II) oxide again.
25. A metal will be recycled only if it is economical to do so. Gold is very expensive. On the other hand, the cost of extracting iron from iron ore is low. In comparison, the cost of recycling iron from scrap iron may be even higher in some cases.
26. (a) The factors to be considered in each case are:
(i) no wind-borne pollution B has advantages (ii) and (iii) only.
(ii) development area payment C has advantage (iii) only.
(iii) deep water port. D has advantages (ii) and (iii) only.
A has all the 3 advantages. E has none of the advantages.
(b) A is the best site.
(c) The aluminium refinery should be situated near electric power stations.
(d) A metal company will recycle used metal only if it is economical to do so. The company has to work out the total cost of collecting the scrap, transporting it, sorting the metal out, melting it down, getting rid of impurities, and cost of storage etc.
27. (a) (There is no specific answer for question 27.)
28. (a) 50 years
(b) (i) Reusing copper articles.
(ii) Recycling used copper.
(iii) Replacing copper by other materials.
(c) There are probably metal ores deep in the Earth's crust that we do not yet know about. With advanced modern technology (e.g. satellite surveying), it is possible to detect and mine such ores.
(d) Aluminium