Question

you have learned about several different methods for the separation and purification of organic compounds (recrystallization, several types of distillation, extraction, chromatography). Prepare a table and write a short paragraph comparing these methods in terms of sample requirements, advantages, drawbacks, etc

Answer 1

Recrystallization: It is based on the principle that the solubility of solid substances in a solvent like water increases with increase in temperatue. In recrystallization, the impure substance is dissolved in a solvent like water and heated to prepare a highly concentrated solution. Now the solution is allowed to cooled down that causes a decrease in the solubility. The impure substances start recrystallize before the pure substance and a situation comes when almost all of the  impure substances are recrystallized leaving only pure substance in the solution. Now the solution undergoes filtration to to obtain the pure substance. The advantage of recrystallization is that a very pure substance can be obtained if carried out effectively. The disadvantage is that it take a long time to purify. Distillation is based on the difference in boiling point of different constituents present in the solution. In distillation the solution is heated until the constituent with low boiling point is completely evaporated. Now the vapor is condensed to ontain pure substance. Pure substance can be obtained by distillation, however it requires a lot of heat and substances with higher boiling point are difficult to separate by this process. The process of extraction uses two different immisible phases to separate a solute from one phase to another. The advantage is that it requires less energy and the disadvantage is that the level of separation depends on the distribution ration of the substance in each layer. Chromatography is based on different migration rate of the constituents in mobile phase. The equipments required are columns, frits, flow cells, pumps, detector, collectors and mass spectrometer. The advantages are even a small quantity of a substance can be detected by chromatography and hence give highly accurate result, it can separate constituents from cmplex mixtures, and different type of chromatograph equipments are available for different type of mixtures. The disadvantage is that Chromatography equipment are costly and skilled persons are required to operate.