Why is Dropwise Addition Preferred in Recrystallization Process?

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Adding the second solvent dropwise during recrystallization is crucial for achieving better purification and larger, purer crystals. This method allows for a gradual decrease in solubility, promoting slow crystallization rather than "crashing" the compound out of solution all at once. A sudden addition can lead to poor contact between the solute and solvent, resulting in smaller, less pure crystals. The dropwise approach enhances the interaction between the compound and the solvent, facilitating a more controlled crystallization process.
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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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