A student performs the following steps to isolate biphenyl from a solid 1:1 mixt
ID: 1049310 • Letter: A
Question
A student performs the following steps to isolate biphenyl from a solid 1:1 mixture of bipnenyl and salicylic acid. Dissolve 2.0 grams of the mixture in 20 mL of ether Extract the ether layer 2-3 times with an aqueous solution of 5% sodium bicarbonate Add2-3 spatula tips of sodium sulfate to the ether layer Extract the ether layer with a saturated aqueous solution of sodium chloride. 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.Explanation / Answer
Clearly there is excess of material, since 1.23 g were recolected
this is also why the melting point range is wide, since it is not a pure component:
the step in biphenyl + salicylic acid must be carried out as follows:
add NaOH, so the salicylic acid becomes a salt which is soluble ONLY in the aqueous solution
since this was not the case, the acid also interacts with ether, and some acid is therefore transferred to the organic layer
that is why you end up with more material, since acid is still present
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