Why is Dropwise Addition Preferred in Recrystallization Process?

[cloveryeah]

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??

 

[Bystander]

improve the purification?

Yes. "Why How?" Do you really want everything dropping from solution at once?

 

[cloveryeah]

is it for the compound to have a better contact with the solvent?

 

[Bystander]

better contact

"Dissolved" is dissolved. There are no degrees of dissolution.

recrystallization

What is the definition of the word "REcrystallization?"

 

[vemvare]

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.