extraction of metals Flashcards
what type of process if ore is an oxide of metal
reduction (loses oxygen)
what elements are extracted by electrolysis
potassium, sodium, lithium, calcium, magnesium, aluminium
what types of metals are extracted by heating with reducing agent and what type of reducing agent is
zinc, iron
carbon or carbon monoxide
what are elements that are found as pure
copper, silver, gold
copper may be extracted from its ore by heating with carbon/hydrogen
raw materials that are added into the top of blast furnace
iron ore (hematite), coke (impure form of carbon) and limestone.
where is hot air blown in from in a blast furnace
bottom
what happens in zone 1 of blast furnace
- coke burns in the hot air forming CO2. exothermic, so heats up the furnace.
what happens in zone 2 of blast furnace
- at high temps, more coke reacts with CO2 forming CO (reduction)
what happens in zone 3 of the blast furnace
- CO reduces iron (III) oxide in the iron ore to form iron (lose oxygen). Iron melts and collects at the bottom of the furnace where it is tapped off
- limestone (calcium carbonate) is added to furnace to remove impurities in ore (calcium carbonate thermally decomposes to form calcium oxide)
- calcium oxide formed reacts with silicon dioxide (impurity in iron ore) to form calcium silicate
- melts and collects as molten slag floating on top of the molten iron, which is tapped off seperately
equation for burning of coke to CO2
C (s) + O2 (g) -> CO2 (g)
reduction of CO2 to CO
CO2 (g) + C (s) -> 2CO (g)
reduction of iron (III) oxide by CO
Fe2O3 (s) + 3CO (g) -> 2Fe (l) + 3CO2 (g)
thermal decomposition of calcium carbonate (limestone) to produce calcium oxide
CaCO3 (s) -> CaO (s) + CO2 (g)
formation of slag
CaO (s) + SiO2 (s) -> CaSiO3 (l)
what is iron ore called
hematite
what is aluminium ore called
bauxite (contains aluminiun oxide)
why cant aluminium be extracted by reduction using carbon
it is higher in the reactivity series
what is aluminium extracted by
electrolysis
process of aluminium extraction by electrolysis
- bauxite purified to produce aluminium oxide Al2O3
- aluminium oxide dissolved in molten cryolite
- mixture placed in electrolysis cell
- graphite lining acts as negative electrode with several large graphite blocks as positive electrode
- at cathode: aluminium ions are reduced, molten aluminium forms at bottom of the cell, molten aluminium is siphoned off from time to time and fresh aluminium oxide is added to the cell
- at anode: oxide ions are oxidised, oxygen produced at anode
what is the use of cryolite in aluminium extraction
aluminium oxide has mp of over 2000C which would use alot of energy and be very expensive. the resulting mixture has a lower melting point without interfering with reaction
what is electroylsis cell made of in aluminium extraction
made from steel, lined with graphite
what is ionix half equation for aluminium at cathode
Al+3 + 3e- -> Al
What is ionic half equation for oxidation of oxide ions
2O-2 -> O2 + 4e-
what is overall equation for reaction during aluminium extraction
2Al2O3 -> 4Al + 3O2
what happens to the graphite in the anodes in aluminium extraction
carbon in graphite reacts with oxygen to produce CO2, resulting in anode wearing away and having to be replaced regularly
what is bad about extraction of aluminium by electroylsis
alot of electricity required, so major expense
what is a metal displacement
when a more reactive metal displaces a less reactive metal from its compound
2 examples of metal displacement
- reacting metal with metal oxide (by heating)
- reacting a metal with an aqueous solution of a metal compound
