You have been given the task of purifying a 60 mL sample of toluene. In order to

Question

You have been given the task of purifying a 60 mL sample of toluene. In order to develop our plan of action, you asl about the impurities likely to be present in the sample. You are told that it contains small amounts of acetone (-10%).

A. Which technique would you choose for the purification process? Why?

B. Clearly decribe the procedure you would use.

C. How will you know, from scrutinizing a H NMR spectrum of the purified toluene, that it has been freed from its impurities? Which signals would indicate the presence ansence of the impurity described above? Explain your rationale.

Explanation / Answer

A. The boiling point of toluene is 110.6 C and that of acetone is 56 C. Since the difference in boiling points is greater than 25 C, simple distillation can be used for the purification process.

B. In distillation, the impure substance is heated in a distillation flask. The vapors are passed through a condenser and collected in a flask. When the mixture of toluene and acetone is heated, acetone begins to vaporize at around 56 C. This is collected separately. Once the temperature crosses 56 C, we can assume that only negligible amounts of acetone remain. So the toluene sample is purified.

C. The HNMR spectrum of the purified toluene can be analyzed for the presence of acetone. This is because the protons in acetone give a characteristic signal. Protons in acetone give a pentet at a chemical shift value of 2.05. By analyzing the HNMR spectrum, the purity of toluene can be verified.

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