Question

During electrolysis of CuSO4 solution using platinum [cathode] and carbon [anode]:
(i) State what you observe at the cathode and anode.
(ii) State the change noticed in the electrolyte
(iii) Write the reactions at the cathode and anode.

August 8, 2024

Answer

(i) At cathode : Cu²⁺ ions and H¹⁺ ions migrate to the cathode. Cu²⁺ ions are discharged in preference to H¹⁺.

At anode : SO₄^2- and OH^1- ions migrate to the anode but OH^1- ions are discharged since they are lower in the electrochemical series.

(ii) The blue colour of CuSO₄ solution fades since the blue Cu²⁺ ions which are discharged at the cathode are not replaced at the anode.

(iii) Cathode : Cu²⁺ + 2e^– ⟶ Cu

Anode: OH^1- – 1e^– ⟶ OH x 2

[2OH ⟶ H₂O + [O]]

4OH ⟶ 2H₂O + O₂

💡 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