Experiment 65

Objective

To identify phenol using the Liebermann test, which involves a sequence of color changes indicating the presence of phenolic compounds.

Introduction

In the Liebermann test, phenol reacts with sodium nitrite (NaNO₂) and sulfuric acid (H₂SO₄) to produce a green solution, which becomes red upon dilution with water. Further addition of sodium hydroxide (NaOH) transforms the solution to a deep blue, indicating the formation of various phenolic complexes.

Materials

Chemicals

●      Phenol

●      Sodium nitrite (NaNO₂)

●      Sulfuric acid (H₂SO₄)

●      Sodium hydroxide (NaOH)

●      Distilled water

Apparatus

●      Test tube

●      Test tube holder

●      Tissue paper

●      White paper for color observation

Reagents

●      3-4 mL of phenol with additions of NaNO₂, H₂SO₄, and NaOH

Procedure

1.    Preparation of Test Solution

o   Place 3-4 mL of phenol in a test tube and add solid NaNO₂, followed by a few drops of H₂SO₄.

2.    Observation of Color Changes

o   A green color should appear, indicating the formation of para-nitrosophenol.

3.    Addition of Water

o   Add distilled water to the test tube. The solution turns red, indicating the formation of indophenol.

4.    Addition of Sodium Hydroxide

o   Add a few drops of NaOH. The solution turns deep blue, indicating the formation of a sodium indophenol complex.

Observation

The test proceeds with distinct color changes: green (para-nitrosophenol), red (indophenol), and finally blue (sodium indophenol complex).

Questions

1.    Why are NaNO₂ and H₂SO₄ used in the Liebermann test?

2.    What color indicates para-nitrosophenol formation?

3.    What color indicates the formation of the indophenol compound?

4.    What is the purpose of the Liebermann test?

5.    How is the Liebermann test useful in phenol identification?