Why use recrystallization for the purification of aspirin?

Question

Why use recrystallization for the purification of aspirin rather than filtration or evaporation??

Answer 1

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Filtration alone ----> Aspirin will not be sufficiently pure .

Recrystallization & followed by Filtration ----> Purer Aspirin ; Most impurities stay in solvent ; Minimum amount of solvent adhere to filtered Aspirin ( can be easily dried ) .

Evaporation ( of Solvent ) ----> certain impurities may not vaporise and stay with Aspirin ; Aspirin may also decompose ( due to prolong exposure to heat ) .

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Asker's Comment:

Thanks!

Answer 2

use recrystallisation as the impurities stay in solution when the solution is acidified. the aspirin or acetyl-salicylic acid is insoluble in acidic conditions. you then filter off and rinse with acid. you then dissolve and filter again in case any insoluble impurities got caught up in the crystal. you then acidify again to recrystallise and filter off liquid. this will leave pure aspirin. don't forget to dry it!.

doing it with evaporation will leave all the impurities in the crystals and you may not even get the desired product!

Answer 3

Recrystallization is able to yield a more pure final product than the other methods and when dealing with drugs that are meant for human consumption purity is king.