Question

Write equations for the reactions taking place at the two electrodes during the electrolysis of:
(i) Acidified CuSO4 solution with copper electrodes.
(ii) Molten PbBr2 with inert electrodes. (mention clearly the name of the electrode in each case)

August 9, 2024

Answer

(i) Electrode — Cathode : Copper, Anode : Copper

Dissociation of aq. CuSO₄ :

CuSO₄ ⇌ Cu²⁺ + SO₄^2-

H₂O ⇌ H¹⁺ + OH^1-

H₂SO₄ ⇌ 2H¹⁺ + SO₄^2-

Reaction at cathode [pure thin sheet of Cu]:
Cu²⁺ + 2e^– ⟶ Cu [Cu deposited on thin sheet]

Reaction at anode [impure block of active Cu]:
Cu – 2e^– ⟶ Cu²⁺ [product nil – Cu²⁺ ions]

(ii) Electrode — Cathode : Iron or Graphite, Anode : Graphite

Dissociation of molten PbBr₂ : PbBr₂ ⇌ Pb²⁺ (cathode) + 2Br^1- (anode)

Reaction at cathode:
Pb²⁺ + 2e^– ⟶ Pb [product lead metal]

Reaction at anode:
Br^1- – 1e^–⟶ Br
Br + Br ⟶ Br₂

💡 Some Related Questions

The metal oxide which can react with acid as well as alkali is :
1. Silver oxide
2. Copper [II] oxide
3. Aluminium oxide
4. Calcium oxide

Give reason for the following :
In the electrolysis of acidified water, dilute sulphuric acid is preferred to dilute nitric acid.

Give reason for the following :
During electrolytic dissociation of sodium chloride, the sodium ions are discharged at the cathode.

Give reason for the following : The blue colour of aq. copper sulphate does not change when it is electrolysed using copper electrodes.

Give reason for the following : Lead bromide undergoes electrolytic dissociation in the molten state but is a non-electrolyte in the solid state.

Give reason for the following : Electrolysis of molten lead bromide is considered a redox reaction.

Select the correct answer from the list in bracket:
1. The cation discharged at the cathode most readily. [Fe2+, Cu2+, Pb2+, H1+]
2. The anion discharged at the anode with most difficulty. [SO42-, Br1-, NO31-,OH1-]
3. The metallic electrode which does not take part in an electrolytic reaction. [Cu, Ag, Fe, Ni]
4. The ion/s which is/are discharged during electrolysis of aq. CuSO4 using Cu electrode. [Cu2+, SO42-, H1+, OH1-]
5. A covalent compound which in aqueous state conducts electricity. [CCl4, CS2, NH3, C2H4]

Give balanced equations for the electrode reactions involved in the following conversions at the respective electrodes:
1. Aluminium oxide → Oxygen gas ← Copper [II] Sulphate
2. Copper metal → Copper ions → Copper metal
3. Lead [II] chloride → Chlorine gas ← Hydrochloric acid
4. Hydroxyl ions ← Acidified water → Oxygen gas
5. Potassium bromide → Bromine gas ← Lead bromide

Select the correct word from the words in brackets to complete the sentence:
1. The electrode at which anions donate excess electrons and are oxidized to neutral atoms is the …………… [anode/cathode]
2. On electrolysis, Ag1+ and H1+ ions migrate to the …………… [cathode/anode] and …………… [Ag1+/H1+] are discharged.
3. Electrolysis is a / an …………… [oxidation/reduction/redox] reaction in which reduction reaction takes place at the …………… [cathode/anode].
4. According to Arrhenius’s theory the amount of electricity conducted by the electrolyte depends on the …………… [nature/concentration] of the ions in solution.
5. Salts ionize in aq. soln. on passage of electric current to give …………… [negative/positive] ions other than H+ ions.

Complete the table given below:
Nature of Anode Nature of Cathode Ions present in electrolyte Ion/s discharged at Cathode / Anode
1. Electroplating an iron rod with silver
2. Electroplating a copper sheet with nickel
3. Electrorefining of silver
4. Extraction of potassium from KCl
5. Extraction of aluminium from Al₂O₃