metals

Question 1

to extract iron, a blast furnace must:

Answer 1

1. heat the reaction mixture to a very high temperature
2. provide a chemical which can reduce the iron oxide to iron
3. remove other impurities found in the ore, like sand, that would harm the quality of the metal being extracted

Question 2

chemical reactions in the blast furnace

Answer 2

• Carbon + oxygen —> carbon dioxide
  
  • Hot air is blasted in
  • Complete combustion of carbon from coke, using oxygen from air blast
  • Exothermic reaction
• Carbon dioxide + oxygen —> carbon monoxide
  
  • Oxygen gets used up as the hot air moves up the blast furnace
  • Carbon dioxide gas reacts with the coke
  • The incomplete combustion of carbon produces carbon monoxide gas
• Iron(III) oxide + carbon monoxide —> iron + carbon dioxide
  
  • The iron ions in iron(III) oxide are reduced to become molten iron
  • The liquid iron flows downwards and is collected at the bottom

Question 3

reactions that remove the impurities in the iron

Answer 3

• Impurity: carbon
  
  • Carbon + oxygen —> carbon dioxide
    
    • Most of the coke is combusted, but some can dissolve into the liquid iron as an impurity
    • Carbon is more reactive than iron, so the oxygen in the hot blast will react with carbon first, producing carbon dioxide which flows up and out of the blast furnace
• Impurity: sulfur
  
  • Sulfur + oxygen —> sulfur dioxide
    
    • Sulfur impurities react with oxygen to form the gas sulfur dioxide which flows up and out of the blast furnace
• Impurity: silicon
  
  • Calcium carbonate —> calcium oxide + carbon dioxide
    
    • The calcium carbonate in the limestone thermally decomposes to become calcium oxide which is much more reactive
  • Calcium oxide + silicon dioxide —> slag
    
    • Forms slag which is much less dense than iron, so it floats on top

Question 4

combustion of carbon word and symbol equations

Answer 4

carbon+oxygen→carbondioxide

C(s)+O2(g)→CO2(g)

Question 5

production of carbon monoxide (incomplete combustion of carbon) word and symbol equations

Answer 5

carbon dioxide + carbon → carbon monoxide

CO2(g)+C(s)→2CO(g)

Question 6

reduction of iron oxide word and symbol equations

Answer 6

iron(III) oxide + carbon monoxide → iron + carbon dioxide

Fe2O3(s)+3CO(g)→2Fe(l)+3CO2(g)

Question 7

combustion of sulfur word and symbol equations

Answer 7

sulfur + oxygen → sulfur dioxide

S(s)+O2(g)→SO2(g)

Question 8

thermal decomposition of calcium carbonate word and symbol equations

Answer 8

calcium carbonate → calcium oxide + carbon dioxide

CaCO3(s)→CaO(s)+CO2(g)

Question 9

formation of slag word and symbol equations

Answer 9

formation of slag
calcium oxide + silicon dioxide → slag

CaO(s)+SiO2(s)→CaSiO3(l)

Question 10

aluminium electrolysis

Answer 10

• Aluminium oxide is dissolved into a salt called cryolite (AlNa3F6)
• Cryolite does not contain any elements that are less reactive than either aluminium or oxygen
• Cryolite is heated until molten and then aluminum oxide is added to it, causing the melting point of this solution to be between 900-1000 celsius (this temperature is lower than the melting point of steel, so the electrolysis bath can be made from steel)
• As an ionic compound, cryolite also conducts electricity so less energy is needed for electrolysis
• Both the anode and cathode are made out of graphite - BUT the anode must be regularly replaced because in these high temperatures, oxygen will react with the carbon in the anode, slowly eroding the anode away
• Molten aluminium is more dense than the cryolite and aluminium oxide solution and so sinks to the bottom, forming a layer of the liquid metal which can be easily removed

Question 11

why can’t aluminium be electrolyzed from an aqueous solution or molten?

Answer 11

• Aluminium is more reactive than hydrogen so it can’t be electrolyzed from an aqueous solution
• The melting point of aluminium oxide is too high, so it is not possible to electrolyze molten aluminium oxide in a large scale

Question 12

aluminium electrolysis reactions at the electrodes

Answer 12

at the anode: 2Oˆ2- –> O2 + 4eˆ-
The oxide ion is losing electrons, so it is being oxidised.
The oxygen gas produced also reacts with the graphite anode
O2 + C–> CO2
at the cathode: Alˆ3+ + 3eˆ- –> Al
The aluminium ion is gaining electrons, so it is being reduced.
Overall, the balanced ionic equation is this:
2Al2O3 –> 4Al + 3O2