Answer to Question #123680 in General Chemistry for 250300183747

Question

Write a short note on the application of the following for the separation and
purification of organic compounds.
a. Crystallization
b. Chromatography
c. Liquid-liquid extraction
d. Soxhlet extraction

Answer 1

a) Crystallization is a simple, very important and effective way of purification and separation of solids. It is based on the fact that all organic compounds are soluble more in hot that in cold solvents. The situation makes solids dissolve on heating and retain their original state on cooling.

The principle here is that the compound and the impurities have different solubilities in a solvent. A solvent is chosen where the compound to be purified is sparingly soluble, that is, it is sparingly soluble at lower temperature and soluble at a higher temperature. The solution is heated to get a saturated solution, and on cooling, the crystals of the compounds are removed through filtration.

b) Chromatography is an important separation technique used to separate constituent particles of a mixture of substances, to purify the compounds and check the purity of organic compounds. In this technique on a stationary phase (solid or a liquid) a mixture of substance is applied. The mixture of gas or the pure solvent is allowed to move slowly on the stationary phase. Due to which the components of the mixture start separating from one another.

c) Liquid – liquid extraction,also called solvent extraction, can be used to separate a substance from a solution by extraction into another solvent. It can be used either to recover a valuable substance from the original solution, or to purify the original solvent by removing an unwanted component.

d) Soxhlet extraction has been used widely for extracting valuable bioactive compounds from various natural sources. In this extraction, a small amount of dry sample is placed in a thimble, which is placed in a distillation flask containing the solvent of particular interest. During each cycle, a portion of the non-volatile compound dissolves in the solvent. After many cycles the desired compound is concentrated in the distillation flask. The advantage of this system is that instead of many portions of warm solvent being passed through the sample, just one batch of solvent is recycled.