Chemistry
Explain why it is preferable to use a number of graphite electrodes as anode instead of a single electrode, during the above electrolysis.
Metallurgy
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Answer
The oxygen evolved at the anode escapes as a gas or reacts with the carbon anode. The carbon anode is thus oxidized to carbon monoxide which either burns giving carbon dioxide or escapes out through an outlet. [2C + O2 ⟶ 2CO; 2CO + O2 ⟶ 2CO2] The carbon anode is hence consumed and renewed periodically after a certain period of usage. It is therefore preferable to use a number of graphite electrodes as anode instead of a single electrode.
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Write the equation for the reaction where the aluminium oxide for the electrolytic extraction of aluminium is obtained by heating aluminium hydroxide.
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(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 ?
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