Experiment 32

Objective

To identify ammonia using Nessler’s reagent.

Introduction

Nessler’s reagent, which contains potassium mercuric iodide in an alkaline solution, reacts with ammonia to produce a brown precipitate, confirming the presence of ammonia. When ammonium salts are treated with a strong base, ammonia gas is released, which subsequently reacts with Nessler’s reagent.

Reaction:

1.    Ammonia release:

NH4​Cl + KOH → KCl + NH3 ​+ H3​O

2.    Reaction with Nessler’s reagent:

Hg2I4 + 2NH3 → NH2 [Hg2I2] + NH4I (brown precipitate)

Materials

Chemicals

·       Ammonium chloride (NH₄Cl)

·       Nessler’s reagent

Apparatus

·       Test tube

·       Test tube holder

·       Dropper

Reagents

·       Prepare a solution by dissolving 3.269 g of ammonium chloride in 250 ml of distilled water in a test tube.

·       Add 5–6 ml of Nessler’s reagent to the solution.

Procedure

1.    Place the ammonium chloride solution in a test tube.

2.    Add Nessler’s reagent to the solution.

3.    Wait for a minute and observe any color change.

Observation

A brown precipitate forms in the solution, indicating the presence of ammonia.

Questions

1.    What is ammonia?

2.    What is Nessler’s reagent?

3.    What color forms during the reaction with Nessler’s reagent?

4.    How does Nessler’s reagent react with ammonium salts?