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Concentration of Ore

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Explain with reason why the graphite anode has to be replaced in the electrolytic reduction of Alumina

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Solution

Dear Student,

In the electrolytic reduction of alumina, oxygen is evolved which goes to anode and reacts with graphite to give CO₂or CO. This prevents the oxidation of aluminium by oxygen. In doing so, the graphite gets consumed and thus needs to be replaced.

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Explain with reasons:

(a) In the electrolytic reduction of alumina, the graphite anode is gradually consumed.

or

Why the anode has to be replaced in this process?

(b) Roasting is carried out on sulphide ores and not on carbonate ores.

(c) Carbon can reduce lead oxide but not aluminium oxide.

(d) Electrolytic reduction is done to obtain aluminium?

(e) Why 'the food containing iron salts' should not be cooked in aluminium utensils?

Q. Anodic product in the electrolytic reduction of alumina:

Q. Which of the following statements is correct?
(i) Copper is extracted by hydrometallurgy from low-grade ores.
(ii) In the electrolytic reduction of alumina, graphite is acting as an anode and steel vessel with the lining of carbon acts as an anode.
(iii) In Hall-Heroult process, aluminium is obtained at anode and CO and

C O_{2}

are produced at the cathode.

Q. (i) Name the solution used to react with Bauxite as a first step in obtaining pure aluminium oxide, in the Baeyer's process.
(ii) Write the equation for the reaction where the aluminium oxide for the electrolytic extraction of aluminium is obtained by heating aluminium hydroxide.
(iii) Name the compound added to pure alumina to lower the fusion temperature during the electrolytic reduction of alumina.
(iv) Write the equation for the reaction that occurs at the cathode during the extraction of aluminium by electrolysis.
(v) Explain why it is preferable to use a number of graphite electrodes as anode instead of a single electrode, during the above electrolysis.

Why is $A l$ obtained only by electrolytic reduction of alumina (pure)?

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