Question

Can an impure sample of citronellal be purified by recrystallization? Justify your answer.

Answer 1

The most commonly used process for purification of solid materials by recrystallisation from a solution.

it involves in following steps these are mainly ;

1) the impure materials is dissolved in particular suitable solvent and shake vigorously or boiled at particular point to form saturated solution

2) this solution is filtered after filtration the insoluble substance is removed. the filtered substance is again diluted by using some extra solvent.

3)the solution is cooled the dissolved substance is crystalise out of the funnel

4)the crystals are separate from the mother liquor by using centrifugation or filtration process .by this separation centrifugation process is the best process for separation of small crystals.

5)the crystals are washed from the mother liquor and then cooled with solvent after that the substance is fully dried.

after that the activated charcoal is added by removing some impurities. in this process organic molecules crystallise much more slowly. the filtrate should takes place at room temperature or kept in refrigerator.

in this the impurities are removed by using preliminary purifications such as steam distillation , soxhlet extraction or sublimation.

after that the crystallisation process is repeated several times by using different solvents.

in this mixture by using concentrated sulfuric acid is added drop by drop slowly by stirring .the material is at low melting points sometimes is it convinient to use dilute solutions like acetone or di ethyl ether etc...

the solution is cooled at -78 degrees in dry ice.to give slurry. which is filtered off through a precooled buchner funnel.

however in rare cases, crystallisation is not a satisfactory method of purification,especially the impurities form crystals that are isomorphous with the materialis purified

infact ,the impurities content   may even be greater in such recrystallisation process.

and finally test the impurities and to remove adequately lower their concentrations by suitable chemical manipulations to recrystallisation and the process is repeated and get finally pure substance.