Question

Give the electrode reactions for formation of
(i) Lead metal and bromine vapours from molten PbBr2 using inert electrodes
(ii) H2 and O2 gas [2:1] from acidified water using inert Pt electrodes.

August 9, 2024

Answer

(i) Formation of Lead metal and bromine vapours from molten PbBr₂ using inert electrodes

At cathode:
Pb²⁺ + 2e^– ⟶ Pb

At anode:
2Br^– – 2e^– ⟶ Br
Br + Br ⟶ Br₂

(ii) Formation of H₂ and O₂ gas [2:1] from acidified water using inert Pt electrodes.

At cathode:
4H⁺ + 4e^– ⟶ 4H
2H + 2H ⟶ 2H₂

At anode:
4OH⁺ – 4e^– ⟶ 4OH
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