Extraction of metals Flashcards
1
Q
What 2 states can metals be in?
A
- combined state
- uncombined state
2
Q
What metals are in an uncombined state?
A
unreactive metals:
- gold
- platinum
- silver
3
Q
What metals are in a combined state?
A
mineral ores containing:
- metal oxides
- metal sulfides
- metal carbonates
- metal chlorides
4
Q
Where are most metals found?
A
- in the ground
5
Q
What are metals first combined with?
A
non metals:
- oxygen
- sulfur
- carbon
6
Q
What are metal + non-metal compounds called?
A
- ores
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
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
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
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
11
Q
What are the 2 methods of extraction for metals in their combined states?
A
- reduction with carbon
- electrolysis
12
Q
What is the process of reduction with carbon?
A
- heating the metal compound with carbon
13
Q
What is the process of electrolysis?
A
- using electricity to decompose the molten metal compound
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
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
16
Q
Which redox reaction happens when a metal is extracted from its ore?
A
- reduction
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
18
Q
what metals require electrolysis to extract the metal from its ore?
A
- metals high up in the reactivity series
- (K - Al)
19
Q
What metals can be extracted from its ore using reduction with carbon?
A
- middle order metals
- (Zn - Pb)
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)
21
Q
What is an ore of iron?
A
- haematite
22
Q
Where is iron extracted from its ore?
A
- in the blast furnace
23
Q
What are the raw materials present at the top of the blast furnace?
A
- haematite (Fe2O3)
- coke (C)
- limestone (CaCO3)
24
Q
What is the blast furnace lined with?
A
- refractory materials
- e.g. aluminium oxide, magnesium oxide
25
Why is the blast furnace lined with refractory materials?
- high melting point
- traps heat
26
What are the reactions that occur in the blast furnace?
- 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
27
how is carbon dioxide produced in the blast furnace?
- coke burns in hot air
- carbon dioxide is produced
28
What kind of reaction is the production of carbon dioxide (exothermic/endothermic)?
- highly exothermic
- temperature in this part of the furnace rises to 1900 degrees celcius
29
How is carbon monoxide produced in the blast furnace?
- carbon dioxide reaction with hot coke to produce carbon monoxide
30
How is an iron ore reduced in the blast furnace?
- carbon monoxide (powerful reducing agent) reduces iron(lll) oxide to molten iron
31
Where does molten iron go?
- falls to the bottom of the blast furnace
- tapped off
32
Why is limestone present in the furnace?
- to remove impurities
33
What is the main impurity in iron?
- sand (silicon dioxide)
34
what happens to limestone inside the furnace?
- it decomposes to quicklime (calcium oxide) and carbon dioxide
35
What is slag?
- calcium silicate
36
How is slag formed?
- calcium oxide reacts with silicon dioxide from sand in iron ore to form calcium silicate (slag)
37
What is slag used for?
- used in road foundations
38
Where does slag go in the blast furnace?
- floats on top of molten iron
39
What is carbon dioxide considered as?
- hot waste gas
40
Where does carbon dioxide escape from and what else escapes with it
- from the top of the furnace
- together with nitrogen and carbon monoxide
41
What is the purity state of iron produced in the blast furnace?
- impure
42
What are the impurities in iron produced in the blast furnace?
- carbon
- other non-metals
43
What is impure iron produced in the blast furnace called?
- cast iron
- pig iron
44
What are the characteristics of pig iron/cast iron?
- very brittle
- has limited uses
45
What happens to pig iron/cast iron?
- converted into steel
46
What is mild steel?
- low carbon steel
47
What are the characteristics of mild steel?
- malleable
- easy to shape
48
What is mild steel used for?
- making car bodies
- machinery
49
What is the relationship between the amount of carbon added and the strength of the steel?
- the more carbon added, the stronger the steel
50
Why is steel stronger when more carbon is added?
- carbon impurity strengthens the iron lattice
- makes it difficult for atoms to slide over one another
51
What are the characteristics of high carbon steel?
- strong but brittle
52
Why is high carbon steel brittle?
- too much disruption of layers
- when a force is applied, metal fractures
53
What is high carbon steel used to make?
- cutting and boring tools
- e.g. knives, hammers, chisels etc
54
What are the properties of stainless steel?
- durable
- resistant to corrosion
55
What is stainless steel used for?
- cutlery
- surgical instruments
56
What are the essential conditions for rusting?
- oxygen
- water
57
what is rust?
- hydrated iron(lll) oxide
58
What speeds up rusting?
- presence of sodium chloride
- presence of acidic substances
59
What are the different methods of prevention of rusting?
- placing a barrier around the metal
- sacrificial protection
- using a rust-resistant alloy such as stainless steel
60
What are some examples of placing a barrier around the metal?
- painting
- greasing
- covering with plastic
- electroplating
61
How is sacrificial protection done?
- a more reactive metal (like magnesium or zinc) is attached to the iron object
62
Why does sacrificial protection work?
- more reactive metal corrodes in preference to the iron
63
How is galvanised steel produced?
- dipping steel into molten zinc
- oxidises more readily than iron
64
What is sacrificial protection useful for?
- underground steel or iron objects like pipes or storage tanks
65
Why is sacrificial protection useful in certain cases?
- when objects are difficult to paint or grease
- but easy to attach a piece of magnesium or zinc
66
Why does sacrificial protection work?
- more reactive metal loses electrons more readily than iron
67
Why should we recycle metals?
- 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
What are commonly recycled metals?
- aluminium (drink cans)
- iron (scrap metal)
- lead (car batteries)
69
What are the advantages of recycling metals?
- 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
What are the economic impacts of recycling metals?
- recycling can be more expensive than extracting metals from their ores
- costs are incurred to collect, sort, separate, clean and transport old metal
71
What are the social impacts of recycling metals?
- time and effort are needed for communities and businesses to practice recycling as a lifestyle
72
What are the environmental impacts of recycling metals?
- recycling can cause pollution problems
- e.g. harmful gases for produced when lead from car batteries is recycled
