Experiment 83

Objective

To prepare benzene in the laboratory from benzoic acid through dry distillation with sodium hydroxide and calcium oxide (soda lime).

Introduction

Benzoic acid reacts with a soda lime mixture (sodium hydroxide and calcium oxide) through dry distillation to yield benzene. In this reaction, sodium benzoate forms initially, then decomposes under heat, releasing CO₂ and producing benzene.

Materials

Chemicals

●      Benzoic acid

●      Sodium hydroxide

●      Sodium hydroxide and calcium oxide (soda lime) mixture

Apparatus

●      250 mL glass retort

●      Sand bath

●      Beaker

●      Connecting tube between retort and beaker

●      Spirit lamp

Reagents

●      Benzoic acid: 30-50 g in a conical flask

●      Sodium hydroxide: 20-30 g in a conical flask

Procedure

1.    Setup of Reaction Mixture

o   Place a mixture of benzoic acid and sodium hydroxide in the glass retort.

2.    Heating Setup

o   Position the glass retort in a sand bath.

3.    Condensation Setup

o   Connect a tube from the glass retort to a beaker placed in an ice bath to cool and condense the benzene vapor.

4.    Heating and Reaction

o   Heat the sand bath gently with a spirit lamp, allowing the temperature to rise slowly. This will cause the decomposition of benzoic acid, releasing CO₂ and forming benzene.

5.    Collection of Benzene

o   Benzene vapors condense in the beaker, collecting as an oily liquid.

Observation

Benzene is observed in the beaker as an oily liquid, which can be identified by its distinct properties.

Questions

1.    Why is a glass retort used in this experiment?

2.    What is soda lime?

3.    Draw and label the structure of benzoic acid.