metal extraction

Question 1

extraction of iron

Answer 1

ore = hematite
C + O2 --> CO2
CO2 + C --> 2CO
Fe2O3 + 3CO --> 2Fe + 3CO2
CaCO3 + heat --> CaO + CO2
CaO + SiO3 --> CaSiO3 (slag)

Question 2

iron to steel

Answer 2

- impurities: carbon, phosphorus, silicon & sulfur
> add oxygen = oxides
- SO2 + CO2 are gaseous = escape
> add calcium oxide
- SiO2 + CaO --> CaSiO3
- slag floats on molten iron = removed

Question 3

advantages of recycling metal (5)

Answer 3

• raw materials are conserved
• saves energy
• less pollution
• saves land from extraction
• less waste & disposal problems

Question 4

disadvantages of recycling metal (2)

Answer 4

• more transport = carrying used materials to recycling centres
• energy used in collecting and sorting metals

Question 5

extracting aluminium

Answer 5

• bauxite purified to aluminium oxide
• Al2O3 + cryolite = lower m.p & conducts electricity better
• high current = heat = keeps Al2O3 molten
  > at negative electrode: Al3+ + 3e- –> Al
  > at positive electrode: 2O2- –> O2 + 4e-
• C + O2 –> CO2 so electrodes have to be replaced

Question 6

extracting zinc

Answer 6

• zinc ore (ZnS) = zinc blende
• 2ZnS + 3O2 –> 2ZnO + 2SO2
• C + O2 –> CO2
• CO2 + C –> 2CO
• ZnO + 2CO –> Zn + CO2
  > gaseous state = condensed to liquid zince

Question 7

uses of aluminium (5)

Answer 7

aeroplane bodies = low density
overhead power cables = conduct electricity
saucepans = conduct heat
food cans = non toxic and resistant to corrosion/acids
window frames = resistant to corrosion

Question 8

uses of copper (2)

Answer 8

electrical wires = conduct electricity / malleable

water pipes = bend, non-toxic & unreactive with water

Question 9

types of steel and composition (6)

Answer 9

mild steel: 0.25% carbon
high carbon steel: 0.5 - 1.4% carbon
low alloy steel: 1-5% of other metals (Cr,Ni,Ti)
stainless steel: 20% chromium / 10% nickel
tungsten steel: 5% tungsten
manganese steel: 13% manganese

Question 10

types of steel, uses and properties (6)

Answer 10

mild steel: car bodies & wires = soft / malleable
high carbon steel: tools & chisels = hard
low alloy steel: construction, bridges & high speed tools = hard / strong / low ductility & malleability
stainless steel: cutlery, sinks & chemical plants = strong / resistant to corrosion
tungsten steel: edges of high speed cutting tools = tough / hard at high temperatures
manganese steel: drill bits & springs = very tough / springy