Experiment 33

Objective

To identify the presence of ammonia by using Nessler's reagent.

Introduction

Nessler's reagent, a potassium mercuric iodide (KHgI₃) solution, is used to detect ammonia in an alkaline environment. When ammonium salts react with Nessler's reagent, ammonia gas is released, which further reacts with the reagent, producing a brown precipitate that confirms the presence of ammonia.

Chemical Reactions:

1.    Formation of Ammonia: NH₄Cl + KOH → KCl + NH₃ + H₂O

2.    Reaction with Nessler's Reagent: 2KHgI₃ → 2KI + 2HgI₂ 2HgI₂ → Hg₂I₄

Hg₂I₄ + 2NH₃ → NH₂[Hg₂I₃] + NH₄I

(Brown precipitate formation indicates the presence of ammonia.)

Materials

Chemicals:

●      Ammonium chloride (NH₄Cl)

●      Nessler's reagent

Apparatus:

●      Test tube

●      Test tube holder

●      Dropper

Reagents:

●      Solution: Dissolve 3.269 g of ammonium chloride in 250 ml distilled water for use in the test tube.

●      Nessler’s reagent: Add 5-6 ml of Nessler’s reagent to the solution.

Procedure

1.    Sample Preparation: Place the ammonium chloride solution in a test tube.

2.    Addition of Nessler’s Reagent: Using a dropper, add 5-6 ml of Nessler's reagent to the sample in the test tube.

3.    Reaction Time: Allow the reaction to proceed for a minute, observing any changes.

4.    Observation of Results: Note any color change or precipitate formation.

5.    Observations

6.    A brown precipitate appears in the solution, confirming the presence of ammonia.

Observations

●      A brown precipitate appears in the solution, confirming the presence of ammonia.

Questions

1.    What is ammonia?

2.    What is Nessler's reagent?

3.    What color change is observed during the reaction with Nessler's reagent?

4.    How does Nessler's reagent react with ammonia?