RP10-A-Preparation of a pure organic solid and test's it's purity

Question 1

The preparation of Aspirin

Question 2

Describe the method used to obtain a pure sample of Aspirin?

Answer 2

1. Add approximately 2g of 2-hydroxbenzoic acid to a dry round-bottomed flask, put cork ring and flask on balance
2. Add approximately 4 ml of ethanoic anhydride to the flask using a graduated pipette. ethanoic anhydride is corrosive
3. Add 5 drops of concentrated phosphoric acid to the flask and swirl gently to mix the ingredients. The phosphoric acid acts as a catalyst and is corrosive
4. Fit the flask with a reflux condenser and heat the mixture on a boiling water bath for 10 minutes
5. Carefully add 2ml of tap water in one portion down the condenser. The excess ethanoic anhydride will hydrolyse (to ethanoic acid) you may see the mixture gently boil (the reaction is exothermic)
6. When this reaction has subsided, pour the mixture into about 40ml of cold water in a 100ml beaker. stir and rub the sides of the beaker with a glass rod is necessary to start the crystallisation process.
7. Allow the mixture to stand in an ice-bath to complete the crystallisation
8. Collect the crystals using suction filtration (reduced pressure filtration) and wash the crystals on the filter paper with a small quantity of water
9. allow the aspirin crystals to dry
10. measure the mass of the aspirin made using an electric balance - use this mass to calculate a percentage yield
11. Measure the melting point using the melting point apparatus to check the purity - compare your melting point with the literature value
12. place small amounts of your aspirin sample into a vial - this will be sent to Uni laboratories for Infra-red and Chromatographic (HPLC) analysis