Practical No. 10: Determination of Rate of Corrosion at Different Temperatures for Aluminium
XIII. Interpretation of Results
Maximum weight loss of aluminium occurred in HCl at higher temperature. Corrosion rate increased with temperature for all media. Alkaline medium also showed significant corrosion at elevated temperatures.
XIV. Conclusions and Recommendations
- Conclusion: Metal deterioration is maximum in acidic medium at higher temperatures.
- Recommendation: Handle acids carefully, dry aluminium strips completely before weighing, and maintain accurate temperature control for reliable results.
XV. Practical Related Questions & Answers
Q1. State the acid when maximum change in weight is observed.
- Answer: Maximum change in weight is observed in Hydrochloric acid (HCl) among all the acids tested. This is because HCl is a strong acid and aluminium reacts vigorously with HCl, displacing hydrogen and forming aluminium chloride. The reaction rate is maximum in HCl, leading to the highest weight loss.
Q2. Name the gas liberated when aluminium is dipped in hydrochloric acid.
- Answer: The gas liberated is Hydrogen (H₂).
- Chemical Reaction: 2Al + 6HCl → 2AlCl₃ + 3H₂↑. The hydrogen gas is released as bubbles during the reaction between aluminium and hydrochloric acid.
Q3. Name the compound formed when aluminium reacts with hydrochloric acid.
- Answer: The compound formed is Aluminium Chloride (AlCl₃). The reaction produces aluminium chloride which dissolves in the solution, and the aluminium strip loses weight as it dissolves.
Q4. Mention type of film formed after dipping metal in hydrochloric acid.
- Answer: No protective film is formed when aluminium is dipped in HCl. In fact, the oxide layer (Al₂O₃) which normally protects aluminium from corrosion is also attacked by HCl, exposing the metal surface to further corrosion. However, in HNO₃, a protective passive oxide film is formed.
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