Experiment 44

Objective

To identify the presence of chlorine in a carbonyl compound using the Lassaigne test.

Introduction

In this experiment, the Lassaigne test is used to detect chlorine within a carbonyl compound. Sodium is added to the sample in a fusion tube and heated, causing a reaction between the sodium and the sample. The resulting product is then mixed with distilled water, filtered, and treated with nitric acid (HNO₃) and silver nitrate (AgNO₃). The formation of a white precipitate, which dissolves in ammonium hydroxide, confirms the presence of chlorine in the sample.

Chemical Reactions:

1.    Reaction with Silver Nitrate

NaCl + AgNO₃ → AgCl↓+ NaNO₃

2.    Dissolution in Ammonium Hydroxide

AgCl + 2NH₄OH → Ag[(NH₃)₂]Cl + 2H₂O

(The precipitate dissolves, forming a colorless solution.)

Materials

Chemicals:

·       Sodium metal

·       Ammonium hydroxide (NH₄OH)

·       Supplied sample (containing chloride)

·       Silver nitrate (AgNO₃)

Apparatus:

·       Fusion tube

·       Test tubes

·       Mortar

·       Bunsen burner

·       Test tube holder

·       Filter paper

Reagents:

·       mg sample in fusion tube

·       piece of sodium metal

·       250 ml distilled water (used in mortar)

Procedure

1.    Sample Preparation: Add the sample and a piece of sodium metal to a fusion tube.

2.    Heating: Heat the fusion tube using a Bunsen burner.

3.    Reaction Product Transfer: Break the fusion tube in the mortar and add distilled water to the reaction product.

4.    Filtration: Filter the mixture using filter paper to obtain a clear solution.

5.    Nitric Acid Addition: Transfer 2-3 ml of the filtrate into a test tube and add 1-2 drops of nitric acid (HNO₃), then heat briefly.

6.    Silver Nitrate Addition: Add a few drops of silver nitrate (AgNO₃) to the solution. A white precipitate should form if chlorine is present.

7.    Ammonium Hydroxide Test: Add ammonium hydroxide to the precipitate in the test tube. The precipitate should dissolve, indicating the presence of chloride ions.

Observations

·       A white precipitate forms upon the addition of silver nitrate, indicating chloride ions.

·       The precipitate dissolves in ammonium hydroxide, forming a colorless solution, further confirming the presence of chlorine.

Questions

1.    What is the Lassaigne test?

2.    How is the presence of chlorine identified?

3.    Why is the Lassaigne test necessary?

4.    What color is observed during the chloride test?

5.    What happens when silver nitrate is added to a solution containing chlorine?