Identification of Chlorine in a Carbonyl Compound by Lassaigne’s Test
22nd Nov 2024
Experiment 43
Objective
To identify the presence of chlorine in a carbonyl compound using the Lassaigne’s test.
Introduction
The Lassaigne’s test can detect halogens in organic compounds. In this test, sodium fusion converts chlorine in the compound to sodium chloride, which then reacts with silver nitrate (AgNO₃) to form a white precipitate of silver chloride (AgCl). This precipitate is soluble in ammonium hydroxide, confirming the presence of chlorine.
Reactions:
1. Formation of silver chloride
NaCl + AgNO3 → AgCl ↓ + NaNO3
2. Solubility in ammonium hydroxide:
AgCl + 2NH4OH → Ag[(NH3)2]Cl + 2H2O
Materials
Chemicals
● Sodium metal
● Ammonium hydroxide (NH₄OH)
● Sample containing chlorine
● Silver nitrate (AgNO₃)
● Nitric acid (HNO₃)
Apparatus
● Fusion tube
● Test tube
● Mortar
● Bunsen burner
● Test tube holder
● Filter paper
Reagents
● mg of sample with a piece of sodium metal in a fusion tube
● 250 ml of distilled water in a mortar
Procedure
1. Add the sample and a piece of sodium metal to a fusion tube.
2. Heat the fusion tube using the Bunsen burner until the reaction completes.
3. Break the fusion tube in the mortar and add distilled water to dissolve the reaction product.
4. Filter the solution using filter paper.
5. Take the filtrate in a test tube.
6. Add 1–2 drops of HNO₃ and heat gently.
7. Add AgNO₃ to the solution; a white precipitate of AgCl should form if chlorine is present.
8. Confirm by adding ammonium hydroxide to dissolve the precipitate, forming a colorless solution.
Observation
A white precipitate forms upon the addition of AgNO₃, which dissolves in ammonium hydroxide to form a colorless solution, indicating the presence of chlorine.
Questions
1. What is the Lassaigne’s test?
2. How is the presence of chlorine identified?
3. Why is the Lassaigne’s test necessary?
4. What color is observed in the chloride test?
5. What happens when AgNO₃ is added to a solution containing chlorine?