Organic CHEM

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What is the whole point of using solvent pairs for recrystallization(say a mix of ethanol and water) rather than just using one or the other?

-I know that you use solvent pairs when you solute won't dissolve in either pure water or pure ethanol, but then if the solute won't dissolve in either or, why does it dissolve when the solvent is a mix? That's what's really confusing.
Thanks :)

  • Organic CHEM -

    Often the material is more soluble in one of the solvents than the other. Thus when one of the solvents is lost (evaporates) this forces the material out of solution. In effect this makes a more steep solubility curve than the single solvent.

    Another reason for using a mixed solvent is that the impurities you are trying to remove may be more soluble in one of the pair.

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