Q: Which of these describes an effective recrystallization solvent? 1. The solve
ID: 574823 • Letter: Q
Question
Q: Which of these describes an effective recrystallization solvent?
1. The solvent can dissolve the compound at an elevated temperature but has poor solubility at the ambient temperature.
2. Only a little of the solvent is required to dissolve the compound at room temperature.
3. A large amount of the solvent will completely dissolve the compound at elevated temperatures.
4. The solvent undergoes a reaction with the compound to convert the compound into a crystallized solid.
Q: Which of these TLC results would indicate successful recrystallization according to the given experimental procedure (O = original sample; R = recrystallization product; P = pure sample)?
1. I
2. II
3. III
4. IV
Q: Your lab partner suggests trying the same solvents that worked for TLC for the recrystallization experiments. How should you respond?
1. Consider the time it would save time in the lab procedure
2. Insist on always following the procedure exactly as it is written.
3. Point out that for recrystallization, room-temperature solubility should be poor
4. Explain that TLC solvents depend upon polarity whereas recrystallization solvents do not.
Q: Mandy writes the following in her ELN. Which number in the procedure contains an error?
1. Find a solvent in which the compound is not very soluble at room temperature. Then heat solvent and try again. If the compound dissolves, use this solvent. Start heating some of this solvent in a hot water bath.
2. Set aside a small amount of seed crystal, in case it is needed to jump-start crystallization.
3. Weigh compound before adding to flask. Then add heated solvent in small amounts—only enough for the compound to dissolve.
4. After compound has dissolved, place flask on ice bath and wait for it to crystallize.
Explanation / Answer
Ans 1 : 1) The solvent can dissolve the compound at an elevated temperature but has poor solubility at the ambient temperature
During the recrystallisation procedure , the solute is first dissolved into the solid by heating the solvent on the high temperature. The mixture is then cooled so that the pure solid can crystallise out and the impurities remain in the solvent. So the solvent must be able to dissolve the compound at high temperatures but not at the ambient temperatures.
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