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Question:
- In recrystallization, the goal is to obtain a purified material with maximum recovery? What are the effects of the operations below on purity and recovery? Explain briefly.
a. In the solution step, an unnecessarily large volume of solvent is used.
i. Effect on purity:
ii. Effect on recovery:
b. The crystals obtained are washed with cold solvent.
I. Effect on purity:
II. Effect on recovery:
C. The crystals referred to in (b) are washed with hot solvent.
I. Effect on purity:
II. Effect on recovery:
Answer:
Step 1
Recrystallization is the purification technique. In this technique, the hot solvent is used to dissolve the maximum amount of crystals and the cold solvent is used for the recovery of crystals in a pure form.
The properties of a solvent used for crystallization play a very important role in the recrystallization process.
Step 2
a) In the solution step, an unnecessarily large volume of solvent is used=
i. Effect on purity:
when too much solvent is used for recrystallization then the purity of crystals decreases, as there is the possibility of adding impurities present in the solvent.
ii. Effect on recovery:
when too much solvent is used for recrystallization then the recovery is decreased because the crystals of a product are getting solubilized.
b) The crystals obtained are washed with cold solvent=
i. Effect on purity:
When the crystals are washed with cold water then the purity and texture of crystals are increase.
ii. Effect on recovery:
When the crystals are washed with cold water then the recovery of crystals increases.
C. The crystals referred to in (b) are washed with hot solvent=
i. Effect on purity:
As the crystals are washed with the hot water then crystals are getting dissolved in a hot solvent and due to which a purity decreases.
ii. Effect on recovery:
As the crystals are washed with the hot water then it gets dissolved in a hot solvent and for recovery, we have to dissolve them again in the cold solvent, during this process the rate of recovery may decrease.
