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Question
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.
When bauxite is treated with sodium hydroxide solution, what happens to:
- the aluminium oxide,
- the iron (III) oxide?
Solution
- The aluminium oxide forms sodium aluminate.
\[\ce{Al2O3.2H2O + 2NaOH ->[150^\circ C - 200^\circ C] 2NaAlO2 + 3H2O}\] - The iron (III) oxide does not dissolve in NaOH and is removed by filtration.
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RELATED QUESTIONS
Answer the following questions with respect to the electrolytic process in the extraction of aluminum:
Explain why powdered coke is sprinkled over the electrolytic mixture.
Name the constituents of Bronze.
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Aluminium is extracted from its chief ore bauxite. The ore is first purified and then the metal is extracted from it by electrolytic reduction.
Write an equation for the reaction which takes place at the anode during the extraction of aluminium by the electrolytic process.
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.' |
- Which solution is used to react with bauxite as a first step in obtaining pure aluminium oxide?
- The aluminium oxide for the electrolytic extraction of aluminium is obtained by heating aluminium hydroxide. Write the balanced chemical equation for this reaction.
- Name the element which serves both as the anode and the cathode in the extraction of aluminium.
- Write the balanced chemical equation for the reaction that occurs at the cathode during the extraction of aluminium by electrolysis.
- Give the balanced chemical equation for the reaction which occurs at the anode when aluminium is purified by electrolysis.
The following question relate to the extraction of aluminium by electrolysis.
Name the other aluminium containing compound added to alumina and state the significance.
Describe the role played in the extraction of aluminum:
Cryolite
Name the compound added to pure alumina to lower the fusion temperature during the electrolytic reduction of alumina.
Write the equation for the reaction that occurs at the cathode during the extraction by aluminium by electrolysis.
Write the constituents of the electrolyte for the extraction of aluminium.
