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Chemistry > Extraction of metals > Flashcards

Extraction of metals Flashcards

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1
Q

What 2 states can metals be in?

A
  • combined state
  • uncombined state
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2
Q

What metals are in an uncombined state?

A

unreactive metals:
- gold
- platinum
- silver

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3
Q

What metals are in a combined state?

A

mineral ores containing:
- metal oxides
- metal sulfides
- metal carbonates
- metal chlorides

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4
Q

Where are most metals found?

A
  • in the ground
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5
Q

What are metals first combined with?

A

non metals:
- oxygen
- sulfur
- carbon

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6
Q

What are metal + non-metal compounds called?

A
  • ores
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7
Q

What are the 3 main stages involved in obtaining metals from their ores?

A
  • concentrating the metal ore
  • extracting crude metal from ore
  • refining crude metal
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8
Q

What happens in stage 1 (concentrating the metal ore)?

A
  • earth and rock are removed before the metal is extracted from the ore
  • this causes the metal ore to contain little waste materials
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9
Q

What happens in stage 2 (extracting crude metal from the ore)?

A
  • the metal is extracted by reduction with carbon or using electricity
  • dependant on the position of the metal on the reactivity series
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10
Q

What happens in stage 3 (refining crude metal)?

A
  • other methods such as electrolysis have to be used to further refine metal to obtain pure metal
  • this is due to the metal that is extracted from the ore potentially still containing impurities
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11
Q

What are the 2 methods of extraction for metals in their combined states?

A
  • reduction with carbon
  • electrolysis
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12
Q

What is the process of reduction with carbon?

A
  • heating the metal compound with carbon
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13
Q

What is the process of electrolysis?

A
  • using electricity to decompose the molten metal compound
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14
Q

What is the relationship between how easy it is to extract a metal from its ore and the position of the metal on the reactivity series?

A
  • the higher up a metal is on the reactivity series, the more difficult it is to extract from its ore
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15
Q

Why is a metal higher up on the reactivity series more difficult to extract from its ore?

A
  • the stability of an ore of a metal higher up the reactivity series is greater than one lower down
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16
Q

Which redox reaction happens when a metal is extracted from its ore?

A
  • reduction
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17
Q

Why does reduction occur when a metal is extracted from its ore?

A
  • the metal ion (in the ore) has to gain electrons to form a metal atom
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18
Q

what metals require electrolysis to extract the metal from its ore?

A
  • metals high up in the reactivity series
  • (K - Al)
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19
Q

What metals can be extracted from its ore using reduction with carbon?

A
  • middle order metals
  • (Zn - Pb)
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20
Q

What metals can be extracted from its ore by simply heating it?

A
  • metals at the bottom of the reactivity series
  • (Cu-Ag)
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21
Q

What is an ore of iron?

A
  • haematite
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22
Q

Where is iron extracted from its ore?

A
  • in the blast furnace
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23
Q

What are the raw materials present at the top of the blast furnace?

A
  • haematite (Fe2O3)
  • coke (C)
  • limestone (CaCO3)
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24
Q

What is the blast furnace lined with?

A
  • refractory materials
  • e.g. aluminium oxide, magnesium oxide
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25
Q

Why is the blast furnace lined with refractory materials?

A
  • high melting point
  • traps heat
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26
Q

What are the reactions that occur in the blast furnace?

A
  • production of carbon dioxide
    C(s) + O2(g) —> CO2(g)
  • production of carbon monoxide
    CO2(g) +C(s) —> 2CO(g)
  • reduction of iron ore
    Fe2O3(s) +3CO(g) —> 2Fe(l) + 3O2
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27
Q

how is carbon dioxide produced in the blast furnace?

A
  • coke burns in hot air
  • carbon dioxide is produced
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28
Q

What kind of reaction is the production of carbon dioxide (exothermic/endothermic)?

A
  • highly exothermic
  • temperature in this part of the furnace rises to 1900 degrees celcius
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29
Q

How is carbon monoxide produced in the blast furnace?

A
  • carbon dioxide reaction with hot coke to produce carbon monoxide
30
Q

How is an iron ore reduced in the blast furnace?

A
  • carbon monoxide (powerful reducing agent) reduces iron(lll) oxide to molten iron
31
Q

Where does molten iron go?

A
  • falls to the bottom of the blast furnace
  • tapped off
32
Q

Why is limestone present in the furnace?

A
  • to remove impurities
33
Q

What is the main impurity in iron?

A
  • sand (silicon dioxide)
34
Q

what happens to limestone inside the furnace?

A
  • it decomposes to quicklime (calcium oxide) and carbon dioxide
35
Q

What is slag?

A
  • calcium silicate
36
Q

How is slag formed?

A
  • calcium oxide reacts with silicon dioxide from sand in iron ore to form calcium silicate (slag)
37
Q

What is slag used for?

A
  • used in road foundations
38
Q

Where does slag go in the blast furnace?

A
  • floats on top of molten iron
39
Q

What is carbon dioxide considered as?

A
  • hot waste gas
40
Q

Where does carbon dioxide escape from and what else escapes with it

A
  • from the top of the furnace
  • together with nitrogen and carbon monoxide
41
Q

What is the purity state of iron produced in the blast furnace?

A
  • impure
42
Q

What are the impurities in iron produced in the blast furnace?

A
  • carbon
  • other non-metals
43
Q

What is impure iron produced in the blast furnace called?

A
  • cast iron
  • pig iron
44
Q

What are the characteristics of pig iron/cast iron?

A
  • very brittle
  • has limited uses
45
Q

What happens to pig iron/cast iron?

A
  • converted into steel
46
Q

What is mild steel?

A
  • low carbon steel
47
Q

What are the characteristics of mild steel?

A
  • malleable
  • easy to shape
48
Q

What is mild steel used for?

A
  • making car bodies
  • machinery
49
Q

What is the relationship between the amount of carbon added and the strength of the steel?

A
  • the more carbon added, the stronger the steel
50
Q

Why is steel stronger when more carbon is added?

A
  • carbon impurity strengthens the iron lattice
  • makes it difficult for atoms to slide over one another
51
Q

What are the characteristics of high carbon steel?

A
  • strong but brittle
52
Q

Why is high carbon steel brittle?

A
  • too much disruption of layers
  • when a force is applied, metal fractures
53
Q

What is high carbon steel used to make?

A
  • cutting and boring tools
  • e.g. knives, hammers, chisels etc
54
Q

What are the properties of stainless steel?

A
  • durable
  • resistant to corrosion
55
Q

What is stainless steel used for?

A
  • cutlery
  • surgical instruments
56
Q

What are the essential conditions for rusting?

A
  • oxygen
  • water
57
Q

what is rust?

A
  • hydrated iron(lll) oxide
58
Q

What speeds up rusting?

A
  • presence of sodium chloride
  • presence of acidic substances
59
Q

What are the different methods of prevention of rusting?

A
  • placing a barrier around the metal
  • sacrificial protection
  • using a rust-resistant alloy such as stainless steel
60
Q

What are some examples of placing a barrier around the metal?

A
  • painting
  • greasing
  • covering with plastic
  • electroplating
61
Q

How is sacrificial protection done?

A
  • a more reactive metal (like magnesium or zinc) is attached to the iron object
62
Q

Why does sacrificial protection work?

A
  • more reactive metal corrodes in preference to the iron
63
Q

How is galvanised steel produced?

A
  • dipping steel into molten zinc
  • oxidises more readily than iron
64
Q

What is sacrificial protection useful for?

A
  • underground steel or iron objects like pipes or storage tanks
65
Q

Why is sacrificial protection useful in certain cases?

A
  • when objects are difficult to paint or grease
  • but easy to attach a piece of magnesium or zinc
66
Q

Why does sacrificial protection work?

A
  • more reactive metal loses electrons more readily than iron
67
Q

Why should we recycle metals?

A
  • metal ores are a finite resource
  • we should recycle metals whenever possible
  • world’s reserves of metals may last longer if we substitute metals with other materials or recycle old metal objects
68
Q

What are commonly recycled metals?

A
  • aluminium (drink cans)
  • iron (scrap metal)
  • lead (car batteries)
69
Q

What are the advantages of recycling metals?

A
  • recycling helps conserve limited metal and fossil fuel resources
  • extracting metals uses up fossil fuels for energy production
  • recycling helps reduce environmental problems caused by extraction of metals
  • smelting ores causes air pollution
  • mined land cannot support plant and animal life
  • lots of waste material generated from extraction process (90% of extracted metal ore turns out to be waste)
  • recycling saves cost of extracting metals
  • landfill sites are required for disposal of used metal objects and waste material from metal extraction
70
Q

What are the economic impacts of recycling metals?

A
  • recycling can be more expensive than extracting metals from their ores
  • costs are incurred to collect, sort, separate, clean and transport old metal
71
Q

What are the social impacts of recycling metals?

A
  • time and effort are needed for communities and businesses to practice recycling as a lifestyle
72
Q

What are the environmental impacts of recycling metals?

A
  • recycling can cause pollution problems
  • e.g. harmful gases for produced when lead from car batteries is recycled

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