Question

3. (A) Describe a procedure to solve the following problems in recrystallization technique: a) no crystals are formed when solution reaches room temperature b) oiling out c) presence of colored impurities d) presence of insoluble impurities e) loss of product due to premature crystallization on the fluted filter paper when (10 pts.) doing a gravity filtration.

Answer 1

ans (a) recrystallization is sepration of pure component from impurity attached with it during cooling with a slow rate as temperature drops solubility in solvent of pure component decreases and it starts forming crystalls . at room temperature both pure component and impurity have equal solubility so new crystal formation process stops.to solve this we can use two solvent recrystallization method.the first solvent dissolves at all temperature.

ans b)if oiling out happens in recrystallization process boil the whole solution until oil get dissolves and then allow it for cooling.ifoil get start forming again stirr the solution vigorously until oil droplets break.

ans (c)if coloured impurities are present by using minimum or near boiling solvent we can remove them.

ans(d)if insoluble impurities present then we have to filter the solution to remove them,

ans(e)we can use more amount of solvent for gravity filtration