5 a) extraction and uses of metals

Question 1

5.1 explain how the methods of extraction of the metals in this section are related to their positions in the reactivity series

Answer 1

Metals can be extracted in three different ways: (i)With Carbon and (ii) By electrolysis & (iii)By more reactive material

Metals that are below zinc in reactivity series can be extracted using carbon and carbon monoxide. Carbon is cheap and can also be as the source of heat.

Metals above zinc in reactivity series are usually extracted by electrolysis. Unfortunately, the large amounts of electricity involved make this an expensive process.

If a metal is more reactive than a metal in a compound, the reactive material will displace it and our targeted metal will be extracted.

Question 2

5. 2 describe and explain the extraction of aluminium from purified aluminium oxide by electrolysis, including:
   i. the use of molten cryolite as a solvent and to decrease the required operating temperature
   ii. the need to replace the positive electrodes
   iii. the cost of the electricity as a major factor

Answer 2

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Aluminium is extracted from aluminium oxide which comes from bauxite. Aluminium oxide has very high melting point,

and it isn’t practical toSo aluminiumelectrolyseoxideisdissolved inmoltencryolite toalumini decrease melting point.

The electrolyte is a solution of aluminium oxide in molten cryolite at a temperature of about 1000oC. The molten aluminium is siphoned off from time to time and fresh aluminium oxide is added to the cell. The cell operates at 5-6 volts and with current 100,000amps. The heat generated by the huge current keeps the electrolyte molten. The large amounts of electricity needed are a major expense.

Cathode:

Aluminium ions are attracted to the cathode and are reduced to aluminium by gaining electrons.

Al3+(l) + 3e- ==> Al(l)

The molten aluminium produced sinks to the bottom of the cell.

Anode:

The oxide ions are attracted to the anode and lose electrons to from oxygen gas.

2O2-(l) ==> O2(g) + 4e-

This creates a problem. Because of the high temperatures, the carbon anodes burn in the oxygen to from carbon dioxide. The anodes have to be replaced regularly, and this also adds to the expense of the process.

Question 3

5.3 write ionic half-equations for the reactions at the electrodes in aluminium extraction

Answer 3

At the anode: 2O2-(l) ==> O2(g) + 4e-

At the cathode: Al3+(l) + 3e- ==> Al(l)

Question 4

5.4 describe and explain the main reactions involved in the extraction of iron from iron ore (haematite), using coke, limestone and air in a blast furnace

Answer 4

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Coke is used as the starting material. It is an impure carbon and it burns in how air blast to form carbon dioxide. This is strongly exothermic reaction.

C(s) + O2(g) ==> CO2(g)

At the high temperatures in the furnace, the carbon dioxide is reduced by more carbon to give carbon monoxide.

CO2(g) + C(s) ==> 2CO(g)

Carbon monoxide is the reducing agent. Iron is gained from haematite(Fe2O3)

Fe2O3(s) + 3CO(g) ==> 2Fe(l) +3CO2(g)

The iron melts and flows to the bottom of the furnace, where it can be tapped off.

In the hotter parts of the furnace, some of the iron oxide is also reduced by carbon itself.

Fe2O3(s) + 3C(s) ==> 2Fe(l) + 3CO(g)

Limestone is added to the furnace to remove impurities in the ore. Limestone thermally decomposed to calcium oxide and carbon dioxide. It is an endothermic reaction.

CaCO3(s) ==> CaO(s) + CO2(g)

Silicon dioxide occurs naturally as quartz and it is a form of impurities that needs to be removed. Calcium oxide react with it to form calcium silicate. This melts and trickles to the bottom of the furnace as a molten slag, which floats on top of the molten iron and can be tapped off separately.

CaO(s) + SiO2(s) ==> CaSiO3(l)

Question 5

5.5 explain the uses of aluminium and iron, in terms of their properties.

Answer 5

Uses of aluminium:

Pure aluminium isn’t very strong, so aluminiumrrosionalloy and strong, it has various uses. Like it is used in aero planes, pans etc. For its good conductivity of electricity, it is used as cables.

Uses of Iron: http://www.shawonnotes.com/index/section_5_chemistry_in_industry_igcse_chemistry/0-36
-Most is used to manufacture steel, used in civil engineering (reinforced concrete, girders etc) and in manufacturing.