unit 10 occurrence and extraction of metals (types of ore --> extraction of iron)

Question 1

types of ores

Answer 1

oxide, sulphide, carbonate, halide

Question 2

examples of oxide ore (ore + main metal compound in ore)

Answer 2

bauxite: hydrated aluminium oxide Al2O3.2H2O
haematite: iron (III) oxide Fe2O3

Question 3

examples of sulphide ore (ore + main metal compound in ore)

Answer 3

copper pyrite: copper (II) iron (II) sulphide CuFeS2
cinnabar: mercury sulphide HgS
galena lead (II) sulphide PbS
zinc blende: zinc sulphide ZnS

Question 4

examples of carbonate ore (ore + main metal compound in ore)

Answer 4

calamine: zinc carbonate ZnCO3
magnesite: magnesium carbonate MgCO3

Question 5

examples of halide (made up of halogen + any other element) ore (ore + main metal compound in ore)

Answer 5

rock salt: sodium chloride NaCl

Question 6

steps involved in extraction of a metal from its ore

Answer 6

1. concentration of ore
2. conversion of ore to oxide
3. extraction of metal
4. purification of metal

Question 7

significance of concentration of an ore

Answer 7

remove any unwanted materials from the ore

Question 8

significance of conversion of an ore to oxide

Answer 8

obtain the metal more easily b/c it’s easier to obtain a metal from its oxide than from its sulphide, carbonate or any other from

Question 9

ways to convert an ore into oxide

Answer 9

roasting: concentrated ore is heated with the presence of excess air (commonly used for sulphide ores)
(sulphide ore) + oxygen –> (metal) oxide + sulphur dioxide

calcination: concentrated ore is heated without the presence of excess air (commonly used for carbonate ores)
(carbonate ore) –> (metal) oxide + carbon dioxide

Question 10

ways to extract metal

Answer 10

by electrolysis of molten ores

by using carbon or carbon monoxide (heat with reducing agent)
(metal) oxide + carbon –> (metal) +carbon monoxide
(metal) oxide + carbon monoxide –> (metal) + carbon dioxide

by heating alone
(metal) oxide (heat) –> (metal) + oxygen

Question 11

why do metals need to be purified

Answer 11

metals extracted by methods other than electrolysis of molten ores are generally impure, thus purification is required

Question 12

significance of using cryolite

Answer 12

lower the melting point of metals

Question 13

what happens during electrolysis of molten ores of aluminium

Answer 13

at the negative electrode
Al3+ –> Al + 3e-

at the positive electrode
2O2- –> O2 + 4e-

Question 14

how is the order of discovery of metals related to their reactivity

Answer 14

more reactive –> harder to extract –> discovered later (due to technological advancement)

Question 15

why do we need to reserve metals

Answer 15

metals are non-renewable resources and are limited

Question 16

advantages of recycling metals

Answer 16

reduce mine + reduce damage

natural reserves of metal ores can last longer
the need to mine ores is reduced. damage to the landscape, noise pollution and dust pollution can thus be reduced
fewer pollutants e.g. SiO2 when produced when extracting metals from their sulphide ores
many metals require less energy to recycle them than to extract new ones from ores
less metal waste at landfill sites

Question 17

disadvantages of recycling metals

Answer 17

high cost

recycling a metal is more expensive than extracting a new metal from the earth
cost of separating metals from waste is high, e.g. hard to separate the metals in alloys
high transport costs for collecting scrap metals
difficult to persuade people to dump waste materials into recycling bins

Question 18

advantages of recycling aluminium cans

Answer 18

95% energy saving comparing to extracting aluminium from its ore
aluminium experiences no loss of quality (good quality)