1. A student performs the following steps to isolate biphenyl from a solid 1:1 m

Question

1. A student performs the following steps to isolate biphenyl from a solid 1:1 mixture of biphenyl and salicylic acid a. Dissolve 2.0 grams of the mixture in 20 mL of ether b. Extract the ether layer 2-3 times with an aqueous solution of 5% sodium bicarbonate c. Add 2-3 spatula tips of sodium sulfate to the ether layer d. Extract the ether layer with a saturated aqueous solution of sodium chloride e. Isolate the organic layer and evaporate the ether The solid they collect at the end weighs 1.23 g and has a wide melting point range If the student expected to recover 1 gram of pure biphenyl, explain, based on the procedural information given above, why this student did not see their expected results. Hint: The order of steps in an extraction can be important. 2. The mixture of benzoic acid, biphenyl, and benzocaine used in this experiment is soluble in acetone, a low boiling point organic solvent. Why would this be a poor choice of organic solvent for this experiment? Hint: think about what the requirements are for the solvents in an effective liquid-liquid extraction

Explanation / Answer

1. In step b, the ether layer is washed with the aqueous solution of 5% NaHCO3 solution, which is not strong enough to completely precipitate the sodium salt of salicylic acid. Hence, some salicylic acid is still present along with biphenyl in the ether layer.

That's the reason why after isolating the organic layer (Et2O layer), the amount of the compound obtained is more than 1 gram, i.e. 1.23 g.

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