Why is Dropwise Addition Preferred in Recrystallization Process?

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Discussion Overview

The discussion focuses on the recrystallization process in chemistry, specifically examining the rationale behind the preferred method of adding a second solvent dropwise rather than in a single portion. The scope includes theoretical considerations and practical implications for purification and crystallization quality.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • Some participants suggest that adding the second solvent dropwise may improve purification, although the specific mechanisms are questioned.
  • One participant posits that better contact between the compound and the solvent is a potential reason for the dropwise addition.
  • Another participant emphasizes that the goal is to allow the compound to crystallize slowly, which leads to the formation of larger, purer crystals, contrasting this with the effects of adding the solvent all at once.
  • There is a challenge regarding the definition of "dissolved," with a participant asserting that there are no degrees of dissolution.
  • Concerns are raised about the consequences of "crashing" the compound out of solution by adding the second solvent too quickly, which could hinder the desired crystallization process.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms and implications of dropwise addition, with no consensus reached on the precise reasons for its preference in the recrystallization process.

Contextual Notes

Limitations in the discussion include a lack of clarity on the definitions of key terms and the specific conditions under which the recrystallization process is being evaluated.

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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