Experiment 84

Objective

To prepare bromoform (CHBr₃) in the laboratory from ethanol using bromine and a strong base.

Introduction

Bromoform can be synthesized by reacting ethanol with bromine in the presence of a strong base (KOH or NaOH). The process involves a series of reactions beginning with the oxidation of ethanol to acetaldehyde, followed by substitution reactions with bromine, ultimately forming tribromomethane as a colorless compound.

Reaction Steps

1.    Oxidation of Ethanol

CH3CH2​OH + Br2 → CH3CHO+2HBr

2.    Formation of Tribromo Compound

CH3CHO + 3Br2 ​→ CBr3​CHO + 3HBr

3.    Formation of Bromoform

CBr3​CHO + KOH → CHBr3  + CH3​COOK

Materials

Chemicals

·       Ethanol (CH₃CH₂OH)

·       Bromine solution

·       Potassium hydroxide (KOH)

Apparatus

·       Flask

·       Bunsen burner

·       Stand and sand bath

·       Beaker for bromoform collection

·       Thermometer

·       Pipette

Reagents

·       Mix 3.695 g of KOH with bromine in a flask, and use 10 mL of ethanol in a pipette.

Procedure

1.    Preparation of Reaction Mixture

o   Place the mixture of bromine and KOH in a flask.

2.    Heating

o   Heat the mixture to 60-70°C.

3.    Cooling

o   Cool the mixture in an ice bath.

4.    Addition of Ethanol

o   Gradually add ethanol dropwise until the color of bromine disappears completely.

5.    Formation of Bromoform

o   Bromoform is produced as a colorless solution.

Observation

The red color of bromine fades gradually, resulting in a colorless solution as bromoform is produced.

Questions

1.    How can you confirm the production of bromoform?

2.    What are the uses of bromoform?

3.    What happens when ethanol is added to a mixture of bromine and KOH?