Products of Electrolysis
Chapter: Electrochemistry | Topic: Products of Electrolysis
PRODUCTS OF ELECTROLYSIS
Topic: Products of Electrolysis
Multiple Choice Questions
Q1. During the electrolysis of dilute H₂SO₄ using platinum electrodes, the gas evolved at the anode is:
- Hydrogen
- Oxygen
- Sulphur dioxide
- Chlorine
Q2. During the electrolysis of aqueous NaCl (brine) using inert electrodes, the product at the cathode is:
- Sodium metal
- Chlorine gas
- Hydrogen gas
- Oxygen gas
Q3. The electrolysis of molten NaCl produces sodium metal at the cathode because:
- Na⁺ has a higher reduction potential than H⁺
- Na⁺ is the only cation present
- Water is absent in molten NaCl
- Both (b) and (c)
Q4. When concentrated aqueous NaCl is electrolysed using a mercury cathode, the product obtained at the cathode is:
- Hydrogen gas
- Sodium amalgam
- Chlorine gas
- Oxygen gas
Q5. During the electrolysis of aqueous CuSO₄ solution using copper electrodes, the reaction at the anode is:
- Cu → Cu²⁺ + 2e⁻
- 2H₂O → O₂ + 4H⁺ + 4e⁻
- SO₄²⁻ → SO₂ + O₂ + 2e⁻
- 2H₂O + 2e⁻ → H₂ + 2OH⁻
Q6. The factor that does NOT affect the product of electrolysis is:
- Nature of the electrolyte
- Nature of the electrode
- Colour of the electrolyte solution
- Concentration of the electrolyte
Short Answer Questions
Q7. During the electrolysis of aqueous NaCl, hydrogen gas is liberated at the cathode instead of sodium metal. Explain why this happens, mentioning the relevant electrode potentials.
Q8. Write the reactions occurring at the anode and cathode during the electrolysis of molten NaCl. Name the products obtained.
Q9. During the electrolysis of dilute H₂SO₄ using platinum electrodes, the volume ratio of gases collected at the cathode and anode is 2:1. Explain this observation with the help of electrode reactions.
Q10. What is the 'overvoltage' or 'overpotential' effect? How does it influence the product of electrolysis of aqueous NaCl at the anode?
Q11. During the electrolysis of aqueous CuSO₄ using inert (platinum) electrodes, the blue colour of the solution fades with time. Explain why this happens. What would happen if copper electrodes were used instead?
Q12. List any two factors that determine the product of electrolysis at an electrode. Illustrate with one example for each factor.
Long Answer Questions
Q13. (a) Explain why the products of electrolysis of aqueous NaCl differ when using inert electrodes versus a mercury cathode.
(b) Write the electrode reactions and name the products obtained in each case. What is the industrial name for the process using a mercury cathode?
Q14. (a) Describe what happens during the electrolysis of aqueous CuSO₄ solution using (i) platinum electrodes and (ii) copper electrodes. Write the reactions at both electrodes for each case.
(b) Why is the electrolysis using copper electrodes called "electrorefining"? What is the practical use of this process?
Q15. (a) Draw a neat and labelled diagram of the diaphragm cell used for the electrolysis of brine (aqueous NaCl). Label the anode, cathode, and diaphragm, and indicate the products.
(b) Why is a diaphragm used between the anode and cathode compartments? What would happen without it?
(c) Write the overall reaction for the electrolysis of brine.
Numerical / Application-Based Problems
Q16. In the electrolysis of aqueous NaCl (brine), a current of 50,000 A is passed for 1 hour to produce chlorine gas, hydrogen gas, and sodium hydroxide.
(a) Write the electrode reactions occurring at the anode and cathode.
(b) Calculate the mass of chlorine gas produced at the anode.
(c) Calculate the mass of NaOH produced in the cathode compartment.
(Given: Atomic masses: Na = 23, Cl = 35.5, O = 16, H = 1 u; F = 96500 C mol⁻¹)
Q17. A student performs the electrolysis of dilute H₂SO₄ using platinum electrodes in a Hofmann voltameter. A current of 0.5 A is passed for 2 hours.
(a) Draw a labelled diagram of the Hofmann voltameter showing the gases collected at each electrode.
(b) Write the electrode reactions.
(c) Calculate the total volume of gases collected at STP.
(d) What is the volume ratio of the two gases? Does it match the theoretical prediction?
(Given: Molar volume at STP = 22.4 L mol⁻¹; F = 96500 C mol⁻¹)
Q18. An aqueous solution of CuSO₄ (0.5 M, 500 mL) is electrolysed using platinum electrodes. A current of 2 A is passed for 1 hour.
(a) Write the reactions at the anode and cathode.
(b) Calculate the mass of copper deposited at the cathode.
(c) Calculate the volume of gas evolved at the anode at STP.
(d) What will be the colour of the solution after electrolysis? Explain.
(Given: Atomic mass of Cu = 63.5 u; Molar volume at STP = 22.4 L mol⁻¹; F = 96500 C mol⁻¹)