Experiment 7

Objective

To detect the presence of double or triple bonds in unsaturated organic compounds using a bromine solution.

Introduction

Unsaturated organic compounds with double or triple bonds react with bromine via an electrophilic addition reaction. When bromine reacts with a compound like propene, it forms a colorless dibromo compound, causing the red color of bromine to disappear, indicating the presence of unsaturation.

Reaction:

CH3​CH = CH2 ​+  Br2 ​→ CH3​CH(Br)-CH(Br) (1,2-dibromopropane)

Materials

Chemicals

·       Bromine solution (Br₂)

·       Propene

Apparatus

·       Test tube

·       Test tube holder

·       Dropper

·       White paper (for color contrast)

Reagents

·       5–6 ml of bromine solution in a test tube

·       3–4 ml of propene solution in a pipette

Procedure

1.    Place the bromine solution in a test tube and secure it in a test tube holder.

2.    Add propene dropwise to the bromine solution.

3.    Continue adding until the red color of bromine completely disappears.

4.    Observe and record any changes.

Observation

The red color of the bromine solution disappears, indicating the presence of unsaturation in the compound.

Questions

1.    What is an unsaturated compound?

2.    How is unsaturation determined in organic compounds?

3.    What occurs when bromine reacts with propene?

4.    Why does bromine react with propene?