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Give reasons for the following :

(a) Electrolysis of molten lead bromide is considered to be a reaction in which oxidation and reduction go side, i.e., a redox reaction.

(b) The blue colour of aqueous copper sulphate fades when it is electrolysed using platinum electrodes.

(c) Lead bromide undergoes electrolytic dissociation in the molten state but is a non- electrolyte in the solid state.

(d) Aluminium is extracted from its oxide by electrolytic reduction and not by conventional reducing agents.

(e) The ratio hydrogen and oxygen formed at the cathode and anode is 2: 1 by volume.

(f) In the electrolysis of acidified water, dilute sulphuric acid is preferred to dilute nitric acid for acidification.

(g) Ammonia is unionised in the gaseous state but in the aqueous solution, it is a weak electrolyte.

(h) A graphite anode is preferred to other inert electrodes during electrolysis of fused lead bromide.

(i) For electroplating with silver, silver nitrate is not used as the electrolyte.

(j) Carbon tetrachloride is a liquid but does not conduct an electrolyte.

(k) Potassium is not extracted by electrolysis of its aqueous salt solution.

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(a) During electrolysis of lead bromide, there is a loss of electrons at the anode by bromine and gain of electrons at the cathode by lead. Thus oxidation and reduction go side by side. Therefore, it is a redox reaction.


(b) The blue colour of copper ions fades due to decrease in Cu+2ions and finally, the solution becomes colourless as soon as Cu+2 ions are finished.

(c) Lead bromide dissociates into ions in the molten state whereas it does not dissociate in the solid state. The ions become free when lead bromide is in the molten state but in the solid state, the ions are not free since they are packed tightly together due to the electrostatic force between them. Therefore, lead bromide undergoes electrolytic dissociation in the molten state.

(d) Aluminium has a great affinity towards oxygen, so it is not reduced by reducing agent. Therefore it is extracted from its oxide by electrolytic reduction.

(e) As per electrolytic reactions, 4H+ are needed at the cathode and 4OH at the anode and two molecules of water are produced at the anode. Hence for every two molecules of water, two molecules of hydrogen and one molecule of oxygen are liberated at the cathode and anode respectively.

(f) This is because HNO3 is volatile.

(g) Ammonia is a covalent compound. Therefore, it is unionized in the gaseous state but in the aqueous solution, it gives NH4OH which is a weak electrolyte and dissociates into ions.

(h) Graphite is unaffected by the bromine vapours.

(i) Silver nitrate is not used as an electrolyte for electroplating with silver because the deposition of silver will be very fast and hence not very smooth and uniform.

(j) Carbon tetrachloride is a liquid and does not conduct electricity because it is a covalent compound and there are no free ions present and contain only molecules.

(k) When a potassium salt solution is electrolyzed it forms hydrogen gas at cathode instead of potassium metal. When the ions get separated during electrolysis, H+ and K+ ions migrate to cathode but since H+ lies below K+ ion in activity series of metals, H+ ions get discharged at the cathode and thereby forms hydrogen gas

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