This diagram is used in an aluminium recycling plant training session. Aluminium oxide is dissolved in molten cryolite inside a steel tank. The tank lining ...
Question 1 Report
This diagram is used in an aluminium recycling plant training session. Aluminium oxide is dissolved in molten cryolite inside a steel tank. The tank lining is the negative electrode and graphite blocks connected above the liquid are positive electrodes. The student is told that the process needs a large electrical energy supply. Aluminium is collected at the bottom before it is cast into sheets for drinks cans. Carbon dioxide is released because the graphite electrodes are slowly used in a reaction with oxygen.
(a) Name the product formed at the negative electrode. [1]
(b) State why aluminium oxide must be molten or dissolved before electrolysis can take place. [2]
(c) Complete the ionic half-equation at the negative electrode.
Al3+ + .......... → Al [2]
(d) Which electrode in Fig. 1 is gradually used up? [1]
(e) Give two advantages of recycling aluminium cans instead of extracting aluminium from aluminium oxide. [2]
Answer Details
(a) The product at the negative electrode is aluminium. [1]
(b) Aluminium oxide must be molten or dissolved so its ions are free to move [1]. Moving ions carry charge, so the liquid conducts electricity. [1] In solid aluminium oxide the ions are fixed in place.
(c) \[Al^{3+}+3e^-\rightarrow Al\] The missing term is \(3e^-\) [1], giving the correct balanced half-equation. [1] Aluminium ions gain electrons, so reduction occurs at the negative electrode.
(d) The graphite positive electrode, the anode, is gradually used up. [1]
(e) Two advantages of recycling include using less electrical energy [1] and conserving aluminium ore/reducing mining. [1] Reduced carbon dioxide emissions and less landfill waste are also acceptable.
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