Experiment 59

Objective

To identify the presence of methanal in a carbonyl compound through a colorimetric test.

Introduction

Methanal can be identified by its reaction with 1% phenylhydrazine, 5% potassium ferrocyanide, and concentrated hydrochloric acid (HCl), resulting in a bright pink solution. This color change is a specific indicator for methanal.

Materials

Chemicals

●      1% phenylhydrazine solution

●      5% potassium ferrocyanide solution

●      Methanal (formaldehyde)

●      Concentrated HCl

Apparatus

●      Test tube

●      Test tube holder

●      Beaker

●      Glass stirring rods

Reagents

●      Prepare a 1% phenylhydrazine solution

●      Prepare a 5% potassium ferrocyanide solution

●      10 ml of methanal (sample) in a test tube

Procedure

1.    Place the methanal sample in a test tube and secure it in a test tube holder.

2.    Add 1% phenylhydrazine, 5% potassium ferrocyanide, and concentrated HCl to the test tube.

3.    Mix the solution by gently shaking the test tube.

4.    Wait a few moments for the reaction to proceed.

Observation

A bright pink color forms in the solution, indicating the presence of methanal in the sample.

Questions

1.    How is the presence of methanal identified?

2.    What color is formed during the reaction?

3.    What reagents are used in the methanal identification test?