NEET2002ChemistryElectrochemistryActual
In electrolysis of NaCl when P t electrode is taken then H ₂ is liberated at cathode while with Hg cathode it forms sodium amalgam because:
Options
- AHg is more inert than P t
- Bmore voltage is required to reduce H ⁺ at Hg than at P t
- CNa is dissolved in Hg while it does not dissolve in P t
- Dconcentration of H ⁺ ions is larger when P t electrode is taken
Correct answer
B. more voltage is required to reduce H ⁺ at Hg than at P t
Step-by-step solution
Sodium chloride in water dissociates as: aligned NaCl & Na ⁺+ Cl ⁻ H ₂ O & H ⁺ OH ⁻ aligned When electric current is passed through this solution using platinum electrodes. Na ⁺ and H ⁺ move towards cathode whereas Cl ⁻ and OH ⁻ ions move towards anode. At cathode aligned H ⁺+e⁻ & H H + H & H ₂ aligned An anode aligned Cl ⁻ & Cl +e⁻ Cl + Cl & Cl ₂ aligned If mercury is used as cathode H ⁺ ions are not discharged at mercury cathode because mercury has a high hydrogen over voltage. Na ⁺ ions are dischaged at cathode