Practical No. 08: Determination of Equivalent Weight of Metal using Faraday’s Second Law
XIII. Interpretation of Results
Electrolysis of CuSO₄ and ZnSO₄ in series demonstrated Faraday’s second law. Weights of copper and zinc deposited were proportional to their chemical equivalents. Equivalent weight of zinc was calculated using known equivalent weight of copper.
XIV. Conclusions and Recommendations
- Conclusion: Same quantity of electricity deposits weights proportional to equivalent weights, verifying Faraday’s second law.
- Recommendation: Clean electrodes carefully, maintain constant current, and accurately measure weights for reliable results.
XV. Practical Related Questions & Answers
Q1. Explain the purposes of cleaning copper and zinc cathodes.
- Answer: Cleaning removes impurities, oxide layers, or grease from electrode surfaces. This ensures proper adhesion of deposited metal and accurate weight measurement. Clean surfaces provide better electrical contact and uniform deposition. It prevents contamination of the electrolyte and ensures the reaction occurs properly at the electrode surface.
Q2. Explain why the weight of Copper anode and Zinc anode decreases.
- Answer: During electrolysis, the anodes (positive electrodes) undergo oxidation and dissolve into the electrolyte as metal ions. The copper anode dissolves as Cu²⁺ ions, and the Zinc anode dissolves as Zn²⁺ ions. This dissolution causes a decrease in the weight of both anodes. The mass lost from the anode equals the mass deposited at the cathode.
Q3. Describe the effect of time on the amount of substance deposited for which current is passed.
- Answer: According to Faraday’s laws, the amount of substance deposited is directly proportional to the time for which current is passed when current is constant. W ∝ t. Therefore, longer electrolysis time results in greater deposition of metal on the cathode, provided current remains constant throughout the process.
Q4. Describe the importance of increase in the weight of cathode.
- Answer: The increase in cathode weight indicates successful electrodeposition of metal on the cathode. It confirms that the ions from the electrolyte are being reduced and deposited on the electrode. This increase is used to calculate the electrochemical equivalent and equivalent weight of the metal, making it essential for verifying Faraday’s laws.
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