metals Flashcards
to extract iron, a blast furnace must:
- heat the reaction mixture to a very high temperature
- provide a chemical which can reduce the iron oxide to iron
- remove other impurities found in the ore, like sand, that would harm the quality of the metal being extracted
chemical reactions in the blast furnace
- 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
reactions that remove the impurities in the iron
- 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
- Carbon + oxygen —> carbon dioxide
- 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
- Sulfur + oxygen —> sulfur dioxide
- 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
- Calcium carbonate —> calcium oxide + carbon dioxide
combustion of carbon word and symbol equations
carbon+oxygen→carbondioxide
C(s)+O2(g)→CO2(g)
production of carbon monoxide (incomplete combustion of carbon) word and symbol equations
carbon dioxide + carbon → carbon monoxide
CO2(g)+C(s)→2CO(g)
reduction of iron oxide word and symbol equations
iron(III) oxide + carbon monoxide → iron + carbon dioxide
Fe2O3(s)+3CO(g)→2Fe(l)+3CO2(g)
combustion of sulfur word and symbol equations
sulfur + oxygen → sulfur dioxide
S(s)+O2(g)→SO2(g)
thermal decomposition of calcium carbonate word and symbol equations
calcium carbonate → calcium oxide + carbon dioxide
CaCO3(s)→CaO(s)+CO2(g)
formation of slag word and symbol equations
formation of slag
calcium oxide + silicon dioxide → slag
CaO(s)+SiO2(s)→CaSiO3(l)
aluminium electrolysis
- 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
why can’t aluminium be electrolyzed from an aqueous solution or molten?
- 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
aluminium electrolysis reactions at the electrodes
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