Why is Dropwise Addition Preferred in Recrystallization Process?

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SUMMARY

Dropwise addition of a second solvent during the recrystallization process is preferred to enhance purification and promote the formation of larger, purer crystals. This method allows for gradual reduction in solubility, preventing the compound from precipitating too quickly, which can lead to smaller, impure crystals. The technique ensures better contact between the solute and solvent, optimizing the dissolution process and improving overall crystallization outcomes.

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  • Understanding of recrystallization principles
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Chemists, laboratory technicians, and students involved in organic synthesis and purification processes will benefit from this discussion on recrystallization techniques.

cloveryeah
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In the mix solvent of recrystallization, why it is better to add the second solvent dropwise instead of by one-portion?

i think...is it to improve the purification? but why?? is it increase the time of contacting the solvent so as to achieve a better dissolution??
 
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cloveryeah said:
improve the purification?
Yes. "Why How?" Do you really want everything dropping from solution at once?
 
is it for the compound to have a better contact with the solvent?
 
cloveryeah said:
better contact
"Dissolved" is dissolved. There are no degrees of dissolution.
cloveryeah said:
recrystallization
What is the definition of the word "REcrystallization?"
 
You want the compound to crystallize (=precipitate) slowly so that it forms big, pure crystals. You wanty the solubility of the compound to decrease gradually. "Crashing" the compound out of the solution by adding the second solvent all in one go achieves the opposite of this.
 

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