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Isolation of organic compounds Essay

1. 2.07 g of the mixture of naphthalene and benzoic acid was weighed accurately on a balance. The mixture was then dissolved in 40 ml dichloromethane and the solution was poured into a separatory funnel.

2. 20 ml of aqueous sodium bicarbonate solution was added to the dichloromethane. A stopper was placed on the separatory funnel and was shaken and pressure was frequently released. The 2 liquids separated into clear layers and the lower layer (dichloromethane layer) was tapped into an Erlenmeyer flask. The aqueous layer was placed into a 400 ml beaker. The dichloromethane was placed back in the separatory funnel.

3. The dichloromethane was extracted with 2 more fresh portions of sodium bicarbonate solution. The bicarbonate solutions are combined in the beaker.

4. The dichloromethane was dried with about 10g of anhydrous sodium sulphate for 10 minutes after which the sodium bicarbonate was filtered using the Büchner funnel. The mass of an evaporating dish was measured and the dichloromethane placed in the evaporating dish and placed on steam bath until it evaporated into a solid. The evaporating dish containing naphthalene was weighed to determine the yield.

5. A funnel was placed on the evaporating dish on the steam bath to collect some sublimating crystals which were used to determine the melting point.

6. The bicarbonate extract was acidified with concentrated HCl. A piece of litmus paper showed that it was acidic.

7. The benzoic acid was extracted by shaking it with25ml portions of dichloromethane. The organic extracts were collected in a pre-weighed Erlenmeyer flask and evaporated on the steam bath. The mass of Benzoic acid produced was determined.


(i) Naphthalene: 0.85g; Benzoic acid: 0.71g

(ii) The melting point of Naphthalene: 80-89º c

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