Question

State Faraday's second law of electrolysis. How will the pH of aqueous NaCl solution be affected when it is electrolyzed?

Hint:

Faraday's second law relates the quantity of substance deposited to the amount of electricity passed. Electrolysis of NaCl leads to an increase in pH at the cathode and a decrease at the anode due to the generation of hydroxide and hydrogen ions.

Answer 1

Faraday's Second Law of Electrolysis

Faraday’s second law of electrolysis: "The mass of a substance deposited or liberated at an electrode is directly proportional to the quantity of electricity passed through the electrolyte."

Electrolysis of Aqueous NaCl:

At the anode: 2Cl⁻ → Cl₂(g) + 2e⁻ Chlorine gas (Cl₂) is evolved, and the solution near the anode becomes more acidic (pH decreases).

At the cathode: 2H₂O + 2e⁻ → H₂(g) + 2OH⁻ Hydrogen gas (H₂) is evolved, and the solution near the cathode becomes more alkaline (pH increases).

Explanation:

• At the anode: Chlorine gas is produced, and the solution becomes acidic due to the formation of HCl, which lowers the pH.
• At the cathode: Hydrogen gas is produced, and the solution becomes alkaline due to the formation of OH⁻ ions, which increases the pH.