Recrystallization

1
Recrystallization
Q. 1 Why is the impure solid dissolved in the
minimum quantity of hot solvent? If excess
solvent is used, (a) some of the insoluble
impurities shall remain in the filtrate in step
4. (b) the yield would drop as more solute
will remain in the mother liquor in step 6.
2

• Q.2 Why is hot filtration done in ways as
  described by step 3 ?
• (a) Hot filtration is to minimize
  crystallization of filtrate before leaving
  the funnel.
• (b) A short-stem funnel fitted with a piece
  of fluted filter paper is to speed up the
  filtration so as to minimize crystallization of
  filtrate before leaving the funnel.

3

• Q.3 Why are the crystals washed in ways as
  described by step 6 ?
• (a) Washing the crystals with the mother
  liquor (a saturated solution) can dissolve
  no more crystals.
• ? the yield is not reduced.
• (b) Washing the crystals with cold solvent
  can remove the mother liquor (with impurities
  dissolved) from the crystals.