Question

1. What would be the result if too much solvent were used in isolating and recrystallizing aspirin?

   a. The solid obtained would not be of high purity. b. Less solid would be obtained. Impurities would be less likely to dissolve. Explain

2. Suppose a student fails to completely dry the purified aspirin before weigh in it. How would this mistake influence the calculated percentage of purified aspirin that was isolated?

   a. Make it greater than it should. b. Make it less than it should. c. Would not influence it. Explain

3. Suppose a student got busy cleaning up the work area and allowed the watch glass with purified aspirin to heat on the boiling-water bath for 20 minutes. How would this influence the calculated percentage of purified aspirin that was isolated?

   a. Make it greater than it should. b. Make it less than it should. c. Would not influence it. Explain

4. What dissolved materials are likely to be in the discarded decantate?

   a. only sand b. only aspirin c. only sugar d. two of the three solids listed.

5. Consider the procedure to obtain purified aspirin and decide which of the following statements about the percentage of purified aspirin actually recovered is most likely to be true.

   a. It is equal to the percentage actually in the impure sample. b. It is less than the percentage actually in the impure sample. c. It is greater than the percentage actually in the impure sample.

Answer 1

Ans 1 b) Less solid would be obtained

In recrystallisation procedure , the solution is cooled so that solid can be crystallised but the impurities remain dissolved in it.

When more solvent is used in the recrystallization procedure , the solid does not crystallise or if does so , it does in a very less amount. Much of it stays in the solvent in the dissolved form only. In such a case some of the solvent must be boiled off so that a considerable amount of solid could be obtained.