Chemistry
Answer the following questions:
(a) Name a metal which is found abundantly in the Earth's crust.
(b) What is the difference between calcination and roasting?
(c) Name the process used for the enrichment of sulphide ore.
(d) Write the chemical formula of one main ore of iron and aluminium.
(e) Write the constituents of the electrolyte for the extraction of aluminium.
Metallurgy
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Answer
(a) Aluminium
(b) Differences between calcination and roasting:
| Roasting | Calcination |
|---|---|
| The ore is heated in the excess air. | The ore is heated in the absence of air |
| Generally sulphide ores are roasted and hence sulphur dioxide is given out. | Generally carbonate and hydrated ores are calcinated and hence carbon dioxide and water vapour is given off. |
| 2ZnS + 3O2 ⟶ 2ZnO + 2SO2 | ZnCO3 ⟶ ZnO + CO2[g] |
| Volatile impurities are removed as oxides (SO2, P2O5, As2O3) and the ore becomes porous and more reactive. | Moisture and organic impurities are removed and the ore becomes porous and more reactive. |
(c) Froth floatation process
(d) Chemical formulae of main ores of iron and aluminium are:
| Name | Chemical name | Formula | |
|---|---|---|---|
| Ore of iron | Haematite | Ferric oxide | Fe2O3 |
| Ore of aluminium | Bauxite | Hydrated aluminium oxide | Al2O3.2H2O |
(e) It is a mixture of molten alumina (Al2O3) 20%, cryolite (Na3AlF6) 60% and fluorspar (CaF2) 20%.
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Related Questions
Write the equation for the reaction that occurs at the cathode during the extraction of aluminium by electrolysis.
Explain why it is preferable to use a number of graphite electrodes as anode instead of a single electrode, during the above electrolysis.
The following is an extract from 'Metals in the Service of man, Alexander and street/Pelican 1976'.
'Alumina (aluminium oxide) has a very high melting point of over 2000°C so that it cannot readily be liquefied. However, conversion of alumina to aluminium and oxygen, by electrolysis, can occur when it is dissolved in some other substance'.
(i) Which solution is used to react with bauxite as a first step in obtaining pure aluminium oxide?
(ii) The aluminium oxide for the electrolytic extraction of aluminium is obtained by heating aluminium hydroxide. Write the equation for this reaction.
(iii) Name the element which serves both as the anode and the cathode in the extraction of aluminium.
(iv) Write the equation for the reaction that occurs at the cathode during the extraction of aluminium by electrolysis.
(v) Give the equation for the reaction which occurs at the anode when aluminium is purified by electrolysis.
The following is a sketch of an electrolytic cell used in the extraction of aluminium :
(i) What is the substance of which the electrodes A and B are made?
(ii) At which electrode (A or B) is the aluminium formed ?
(iii) What are the two aluminium compounds in the electrolyte C ?
(iv) Why is it necessary for electrode B to be continuously replaced ?