-Why is it important to add the solvent to the solid, rather than the other way

Question

-Why is it important to add the solvent to the solid, rather than the other way round?
-Why is it important to have solvent left in the recrystallization flask after the solution has cooled and before isolating the crystals by vacuum filtration?


-Why is it important to add the solvent to the solid, rather than the other way round?
-Why is it important to have solvent left in the recrystallization flask after the solution has cooled and before isolating the crystals by vacuum filtration?


-Why is it important to add the solvent to the solid, rather than the other way round?
-Why is it important to have solvent left in the recrystallization flask after the solution has cooled and before isolating the crystals by vacuum filtration?

Explanation / Answer

1). For the purifying solid organic compounds is by recrystallization technique is to be used .

In this technique, an impure solid compound is dissolved in a solvent and then allowed to slowly crystallize out as the solution cools. As the compound crystallizes from the solution, the molecules of the other compounds dissolved in solution are excluded from the growing crystal lattice, giving a pure solid.

2).Crystals will not form if there is a large excess of solvent. If no crystals formed then , a portion of the solvent may need to be removed. This can be accomplished by heating the solution for a period of time in order to evaporate some solvent. The new, concentrated solution, should be cooled to stimulate crystallization should again be attempted.

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