(a) Explain why transition metals
(i) have high melting points
(ii) have variable oxidation states,
(iii) exhibit paramagnetism
(b) (i) Name the impurities present in bauxite
(ii) State how the impurities in bauxite are removed
(ii) Explain why aluminium oxide is said to be amphoteric.
(c) (i) Describe the electrolysis of copper (II) tetraoxosulphate (VI) solution, using copper electrodes.
(ii) Will the colour of the copper (II) tetraoxosulphate (VI) solution change at the end of the electrolysis described in (c)(i) above? Give reasons for your answer.
Explanation
(a)(i) The transition metals are very dense because of their electron filling the inner d-orbitals and hence, they have high melting points.
(ii) The variable oxidation states of the transition metals confer with their stable energies of electrons configuration.
(iii) Para magnetism is the result of parallel spin of the elec-trons at orbitals of high energy.
(b)(i) The impurities present in bauxite are the oxides of iron.
(ii) The impurities sample of bauxite is heated with concentrated solution of sodium hydroxide as a purification process
i.e Al\(_2\)O\(_{3(S)}\) + 6OH\(_{(aq)}\) + 3H\(_2\)O --> 2Al(OH)\(^{3-}_{6(aq)}\)
By reprecipitating, we obtain as follows:
2Al(OH)\(^{3-}_{6(aq)}\) + 6CO\(_{2(g)}\) —> Al\(_{2}\)O\(_3\) + 6HCO\(_{3(aq)}\) + 3H\(_2\)O
(i) (iii) Al\(_2\)O\(_3\) is amphoteric because, it behaves as an acid and a base respectively.
(c)(i) In the electrolysis of copper (ii) tetraoxosulphate (VI) using copper electrodes, elemental copper is precipitated at the cathode while the copper anode ionizes by dissolving in the electrolyte to replace discharged Ceions at the cathode.
(ii) The colour of the electrolyte will not change because as copper ions are discharged at the cathode, they are replaced by the dissolving anode.