A student attempted to perform a recrystallization but after dissolving his acet
ID: 487008 • Letter: A
Question
A student attempted to perform a recrystallization but after dissolving his acetanilide in hot solvent, the sample did not recrystalize when it cooled. What is the most likely thing that the student did incorrectly and how can he correct this error (without starting over)? What should he do in the future to try to avoid this error? Another student chooses a refry stabilization solvent in the following way: he performed the same tests as you did above. He then chooses a solvent that he observed caused the solid to dissolve right away and also dissolved when heated. After attempting to perform the refry stabilization, he failed to recover any solid product. What did this student do wrong? How can he correct this error (without starting over because this is a valuable solid he doesn't have any morel? A student performs the refry stabilization but her crystals are very powdery when they should be more needle- lake-what was the most likely mistake the student mode? How can the student correct this error (without starting over's)? A student finishes her refry stabilization and finds that she has 110% recovery and the melting point is very low. Assuming that she performed her calculation and melting point correctly what is the most likely error the student made? How can she correct this?Explanation / Answer
1. The student has added too much solvent. To rectify, evaporate some solvent to get a concentrated solution.
2. The student has choose a wrong solvent. The a proper solvent should be such that compounds solutibility in hot solvent and cold solvent differes drastically. To rectify : try cooling the solution to very low temp e.g. -10oC
3. Slow cooling will give needle like cryrtals. The student has cooled down the solution rapidly. To rectify this mistake : redissolve in minimum volume of solvent and repeat the procedure
4. This means the product is still impure. Recrystallize one more time
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