Experiment 53

Objective

To identify the presence of glycerine by dehydrating it in the presence of potassium bisulfate or phosphorus pentoxide, producing acrolein, which has a distinct odor.

Introduction

Glycerine undergoes dehydration in the presence of potassium bisulfate (KHSO₄) or phosphorus pentoxide (P₂O₅) to form acrolein, a compound with a distinctive odor. This odor serves as a qualitative indicator of glycerine.

Reaction Overview When glycerine is heated with a dehydrating agent such as KHSO₄ or P₂O₅, it forms acrolein, releasing a pungent odor.

Materials

Chemicals

·       Glycerine

·       Potassium bisulfate (KHSO₄) or phosphorus pentoxide (P₂O₅)

Apparatus

·       Test tube

·       Test tube holder

·       Bunsen burner

·       Protective mask

Reagents

·       10 mL of glycerine with 1-2 drops of potassium bisulfate

Procedure

1.    Preparation of Test Solution

o   Place 10 mL of glycerine in a test tube.

2.    Addition of Dehydrating Agent

o   Add 1-2 drops of potassium bisulfate or a small amount of phosphorus pentoxide to the test tube.

3.    Heating

o   Gently heat the test tube with a Bunsen burner.

4.    Observation of Odor

o   When a distinct odor (acrolein) is detected, stop heating immediately.

Observation

The presence of a pungent acrolein odor indicates the presence of glycerine in the sample.

Questions

1.    Why is potassium bisulfate used in the glycerine test?

2.    How is acrolein formed?

3.    What is acrolein?