Chemistry
(a) Give the chemical names and formulae of the main ores of
(i) aluminium,
(ii) iron and
(iii) zinc.
(b) Which impurities are present in bauxite?
(c) What is red mud, how is it removed?
Metallurgy
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Answer
(i) Ores of aluminium :
| Name | Chemical name | Formula |
|---|---|---|
| Bauxite | Hydrated aluminium oxide | Al2O3.2H2O |
| Cryolite | Sodium aluminium flouride | Na3AlF6 |
(ii) Ores of iron:
| Name | Chemical name | Formula |
|---|---|---|
| Red haematite | Anhydrous ferric oxide | Fe2O3 |
| Brown haematite | Hydrated ferric oxide | 2Fe2O3.3H2O |
(iii) zinc
| Name | Chemical name | Formula |
|---|---|---|
| Zinc Blende | Zinc sulphide | ZnS |
| Calamine | Zinc Carbonate | ZnCO3 |
(b) Bauxite contains 60% aluminium oxide, the rest being sand, ferric oxide and titanium oxide.
(c) Finely grinded Bauxite is heated under pressure with caustic soda. Bauxite dissolves and forms sodium meta aluminate, leaving behind insoluble impurities called red mud. It consists of ferric oxide, sand etc. which are removed by filtration.
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Related Questions
Fill in the blanks:
(a) Usually …………… (sulphide/carbonate) ores are subjected to …………… (calcination/roasting) which is done in the absence of air
(b) Zinc blende is converted to oxide by …………… (roasting/calcination) process.
(c) Froth floatation process is generally used to concentrate …………… ores (sulphides/carbonate)
State the position of aluminium in the periodic table.
In order to obtain 1 tonne of aluminium, the following inputs are required: 4 tonnes of bauxite, 150 kg of sodium hydroxide and 600 kg of graphite. The aluminium compound in bauxite is aluminium oxide and the main impurity is iron (III) oxide. Aluminium is obtained by the electrolysis of aluminium oxide dissolved in cryolite.
(a) When bauxite is treated with sodium hydroxide solution, what happens to
(i) the aluminium oxide
(ii) the iron (III) oxide
(b) (i) Name the process used for the purification of bauxite.
(ii) Write the equation for the action of heat on aluminium hydroxide.
(c) (i) Write the formula of cryolite.
(ii) Write down the word which correctly completes the following sentence:
By dissolving aluminium oxide in cryolite a …………… (conducting/non-conducting) solution is produced.
(iii) Why is so much graphite required for the electrolytic process?
(iv) Write the equation for the reaction which takes place at the cathode
(v) What is the cathode made up of?
Aluminium is extracted from it's chief ore, bauxite. The ore is first purified and then the metal is extracted from it by electrolytic reduction.
(a) Write three balanced equations for the purification of bauxite.
(b) Name a chemical used for dissolving aluminium oxide. In which state is the chemical used?
(c) Write an equation for the reaction which takes place at the anode during the extraction of aluminium by the electrolytic process.