recrystallization a) Why should the solvent not be boiled off as a means of reco
ID: 992704 • Letter: R
Question
recrystallization
a) Why should the solvent not be boiled off as a means of recovering the crystals?
b) How could the addition of too much hot solvent during the dissolving of a crude product lead to loss of yield of product? What could be done to correct this situation?
C) Which type of filtration, gravity or vacuum, is used to remove activated charcoal? Explain why.
D) Indicate the principle by which decolourizing carbon is used in the removal of coloured impurities.
E) What factor affects the size of crystals formed in a recrystallization?
Explanation / Answer
A) The crystal formation should be slow and spontaneous. so we dissolve the compound in hot solution and let is cool down to form crystal.Boiling may cause formation of crystal very fast which cause trapment of impurities from the solvent.
B) Use of too much hot solvent may cause decompsoition of product and hence decrease of yield
C) The use of vacuum filteration may cause boiling of liquid as the pressure is low. the boiling may then cause accumulation of crude /undesireable residue which may remain in the solvent.
D) This is adsorption , the decolourizing carbon is used to remove coloured impurities as the impurities get adsorbed on the charcoal.
E) There are many factors which decide the size of crystal
a) tempearature: a comparative high temperature cause formation of large crystals
b) rate of crystallization also affect the size of crystal, slow formation of crystals results in formation of large crystals
c) Purity of mother liquor also determines the size of crystal.
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