Required practical 10: preparation of a pure organic solid and test its purity

Describe the aspirin practical

• add hydroxybenzoic acid to a pear shaped flask and ethanol anhydride

• Add 5 drops of phosphoric acid and swirl to mix

• Fit the flask with a reflux condenser and heat

• Without cooling ass 2cm of water down the condenser

• When vigorous reaction has ended pour 40cm of cold water

• Collect product by suction filtration

(Crystallisation) why do we wash with distilled water

• remove soluble impurities

(Crystallisation) why do we use a hot filter

• remove insoluble impurities

• Will prevent crystals forming

(Crystallisation) why do we dry between 2 sheets of filter paper

• remove excess water or else mass would be larger and % yield over 100

How do you measure melting point

• place sample in melting point machine

• Put sample in capillary tube

• Heat slowly near melting point

• Compare experimental data with data book value to verify the degree purity

(Purification) why do we use ANHYDROUS sodium hydrogen carbonate

• will neutralise any remaining reactant acid

(Purification) why do we use sodium chloride

Helps seperate organic layer from aqueous layer

Describe the nitration practical

• add methylbenzoate to a small flask and dissolve it in sulphuric acid. Cool mixture in ice

• Add concentrated suburbia acid drop by drop to nitric acid

• Cool in ice

• Now add nitrating mixture drop by drop to methylbenzoate solution and stir with thermometer

• Pour into crushed iced and stir until ice is melted

(Nitration) why do we keep the mixture below 10 degrees

• to prevent multiple substation of nitro groups on benzene ring