I did a chemistry experiment about Aspirin synthesis and recrystalization to get

Question

I did a chemistry experiment about Aspirin synthesis and recrystalization to get pure aspirin

This is my experimental result of melting point of Recrystallized aspirin and crude aspirin.

I have some questions.

1. My experimental results about yield of aspirin were greater than theoretical yield of aspirin. I want to know why yield of aspirin of my sample results were greater than theoretical yield of aspirin.

2. I want to know about the purpose of the Ferric chloried test and what would be the impuriteis in my sample. This is the result of Ferric chloride test. Please explain it in detail.

3. Please explain any difference between the melting points of the crude aspirin and re-crystallized samples of aspirin. Please make estimation of the purity by ensuring the melting point range.

This is my results.

Substance

Melting point

Commercial aspirin

138-140?

Salicylic acid

158-160?

4. Finally I want to know about the sources of error in this experiment.

Substance

Melting point

Commercial aspirin

138-140?

Salicylic acid

158-160?

3. Fernic chloride test Test tube # before color after color 11. salicylic acid Colorless and Co-tress a Violet 2. crude aspirin 3. Recrystallized aspirin 4. blank .ole eak violet weat pellan

Explanation / Answer

1) and 2) May be you had excess sample of Salicylic acid and considered less than that. The mol.wt of salicylic acid is less than the molecular wt of. asprin also. even if the salicylic acid left unreacted also you are nt supposed to get the higher yield. So, you had excees of salicylic acid and by mistake you might did, may be weighing balance problem. And may be solvent content is the second reason.

2) Ferric chlorde gives test for phenols and so salicylic acid is positive for the test.

And crude product of asprin is with unreacted salicylic acid caused the light violet, impringing that your compound is with unreacted salicylic acid also. And the recrystallised asprin is weakly violet in colour resembling, traces of the salicylic acid is now even persisted

3) The melting point is always sharp or vary by a degree for pure compounds. The impurity causes lower melting point generally based on the melting point of impurity and its molar compositions.

So, the lower melting point of your compound seemed to be due to solvent also. my guesss is right.

So, air dry your sample and weigh again and this may be a another reason for increased yield too.

4) Solent may be the major impact in ecess yield, and simultaneously the salicylic acid as unreacted impurity is not negotiable too.

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