Detection of unsturation in a compound

🧪 Detection of Unsaturation Using Potassium Permanganate

Today in our school chemistry lab, we performed a fascinating experiment that helped us confirm the presence of unsaturation in an organic compound. This was not just a theory — it was a live demonstration that thrilled our students. The core idea was to detect the presence of double or triple bonds (unsaturation) using a classical test involving potassium permanganate (KMnO₄).

🌟 Objective of the Experiment

• To detect the presence of unsaturation in a compound (double/triple bonds).
• To observe the decolorization of potassium permanganate in presence of an alkene (ethene).

🧫 Materials Required

• Ethyl alcohol (C₂H₅OH)
• Concentrated sulfuric acid (H₂SO₄)
• Test tube & delivery tube
• Potassium permanganate solution (dilute, light pink)
• Beaker with acetone
• Water bath

⚗️ Procedure Followed in the Lab

1. We took ethyl alcohol in a test tube and carefully added concentrated sulfuric acid dropwise.
2. This setup was gently heated in a water bath to produce ethene (C₂H₄) through elimination reaction.
3. The ethene gas was passed through a delivery tube into a beaker containing acetone.
4. We then added a few drops of dilute potassium permanganate solution to the acetone-ethene mixture.
5. After shaking, we observed the pink color of KMnO₄ disappeared.

🧬 Chemical Reactions Involved

1. Dehydration of Ethanol to Ethene:

C₂H₅OH → C₂H₄ + H₂O (in presence of H₂SO₄ and heat)

2. Reaction of Ethene with KMnO₄:

3C₂H₄ + 2KMnO₄ + 4H₂O → 3C₂H₄(OH)₂ + 2MnO₂↓ + 2KOH

The disappearance of pink color confirms unsaturation!

👨‍🏫 Student Experience

Our students repeated this test several times and each time they observed the same result — the pink color vanished after reaction. They were amazed to witness the concept of organic unsaturation unfold live in front of their eyes.

• "It was so cool to see the color change instantly!"
• "Now I finally understand what unsaturation means!"
• "The experiment was easy to follow and very visual!"

🔬 What is Unsaturation?

Unsaturation refers to the presence of one or more double or triple bonds in a molecule. Saturated compounds contain only single bonds (like alkanes), while unsaturated compounds like alkenes and alkynes contain multiple bonds that can undergo addition reactions.

Potassium permanganate is a good oxidizing agent. It adds to the double bond and oxidizes it, which causes its characteristic purple-pink color to disappear — a clear visual confirmation of unsaturation.

🧠 Learning Outcome

• Students learned to prepare ethene gas from alcohol.
• They identified unsaturation using potassium permanganate.
• Gained hands-on lab experience with safety protocols.

📌 Precautions Taken

• Concentrated sulfuric acid was handled with care under teacher supervision.
• Hot water bath used to avoid direct heating.
• Proper lab coats and goggles were worn.
• Ventilation ensured while generating ethene.

📚 Conclusion

This experiment was a practical demonstration of how chemistry works in real time. The use of potassium permanganate to detect unsaturation not only taught students theoretical concepts but also instilled excitement about lab chemistry. Such visual and interactive experiments are vital to building scientific temper and curiosity in young minds.