Hydrolysis of benzamide

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Experiment 18

Hydrolysis of benzamide

Date: 18-5-2006

Objective

To study the hydrolysis of benzamide into benzoic acid and to determine the melting point of the product.

Introduction

        Benzamide reacts with an alkali and an acid to give benzoic acid under heating.

        The benzoic acid so formed is impure and is purified using a technique called recrystallization. This process involves the dissolving of the acid into boiling water to make a saturated solution and then allowing crystals to form.

        The crystals are then collected by suction filtration.

Procedure

  1. 3 g of benzamide was weighed out and put into a conical flask.
  2. The benzamide was mixed with 50cm3 of NaOH.
  3. The conical flask was fit with a cord and the mixture was heated for about 15 minutes.

 

  1. The gas evolved was tested with a piece of pH paper.
  2. The reaction mixture was cooled and hydrochloric acid was added until a white precipitate was formed.
  3. The residue, then benzoic acid, was obtained by suction filtration.
  4. The benzoic acid was dissolved with minimum amount of boiling water, and the solution was allowed to cool down to initiate the formation of the crystals.
  5. The crystals were obtained by suction filtration and were dried in an oven for 1 night.
  6. The dried crystals were weighed and its melting point range was determined.
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Data and Calculation

  1. The gas evolved in step 4: NH3

Test: the steam was directed to a piece of pH paper to measure the pH. The pH measured was 9.

  1. Color of the crystals obtained after recrystallization: white

Shape of the crystals: needle-shaped

  1. Mass of banzamide + weighing bottle: 7.81g

Mass of weighing bottle: 4.65g

Mass of benzamide: 7.81 – 4.65 = 3.16g

Number of moles of benzamide: 3.16/ (109) = 0.0290moles

  1. Weight of crystals + watch glass: 27.808g

Weight of watch glass: 26.546g

Weight ...

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