Why is Dropwise Addition Preferred in Recrystallization Process?

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In summary, adding the second solvent dropwise in a mix solvent recrystallization process is preferred because it improves the purification and allows for better contact between the compound and solvent, resulting in slower and more controlled crystallization. This leads to larger and purer crystals compared to adding the solvent all at once, which can cause the compound to crash out of solution and result in smaller or impure crystals. The goal of recrystallization is to achieve slow and gradual dissolution of the compound for optimal purification.
  • #1
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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  • #2
cloveryeah said:
improve the purification?
Yes. "Why How?" Do you really want everything dropping from solution at once?
 
  • #3
is it for the compound to have a better contact with the solvent?
 
  • #4
cloveryeah said:
better contact
"Dissolved" is dissolved. There are no degrees of dissolution.
cloveryeah said:
recrystallization
What is the definition of the word "REcrystallization?"
 
  • #5
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.
 

1. What is the purpose of the recrystallization process?

The purpose of the recrystallization process is to purify a solid compound by dissolving it in a suitable solvent and then allowing it to crystallize under controlled conditions. This process is used to remove impurities and obtain a pure sample of the compound.

2. What factors affect the success of the recrystallization process?

The success of the recrystallization process is affected by factors such as the choice of solvent, temperature, and rate of cooling. The solvent should be able to dissolve the compound at high temperatures but not at lower temperatures, and the rate of cooling should be slow to allow for proper crystal formation.

3. How do you determine the appropriate solvent for recrystallization?

The appropriate solvent for recrystallization can be determined by performing a solubility test. The compound is tested in different solvents at varying temperatures, and the one that dissolves the compound at high temperatures but not at lower temperatures is chosen as the recrystallization solvent.

4. Can the recrystallization process be used to remove all impurities from a sample?

No, the recrystallization process can only remove impurities that have similar solubility as the compound. Impurities that have different solubility will remain in the solution even after the compound has crystallized. Other purification techniques may be necessary to remove these impurities.

5. What is the difference between recrystallization and crystallization?

Recrystallization is a purification technique that involves dissolving a compound in a solvent and then allowing it to crystallize under controlled conditions. Crystallization, on the other hand, is a natural process in which a compound solidifies into a crystal structure without any external intervention. Recrystallization is a deliberate process used for purification, while crystallization can occur spontaneously.

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