You have three samples of a compound in unmarked vials: one purified by crystall

Question

You have three samples of a compound in unmarked vials: one purified by crystallization, another not purified, and a third recovered from crystallization of the mother liquor. They melt at 128, 135, and 139°C, respectively, which is which? . Solid cormpoundC contains solid impurity 1 You attempt to purify C by crystallizing from solvent S but when you cool the solution nothing crystallizes. You then evaporate S, leaving solid. a) Is the solid purified C? b) If so, explain how it was purified. If not, explain why it was not purified. 9 10. Consider a crystallization of sulfanilamide in which 10 mL of hot 95% ethyl alcohol is added to 0.10 g of impure sulfanilamide. After the solid has dissolved, the solution is cooled to room temperature and placed in an ice-water bath. No crystals form even after scratching with a glass rod. Explain why this crystallization failed. What would you have to do at this point to make the crystallization work?

Explanation / Answer

The melting point of compounds generally decreases with the presence of impurity

So the most pure compound (crystallized ) will have highest melting point of 139 0C

the one obtained from mother liquor : 135 0C

Not purified : 128 0C

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