NCERT Class XI Chemistry Organic Chemistry Some basic principles and Techniques Solutions

Question : 20

Total: 40

What is the difference between distillation, distillation under reduced pressure and steam distillation?

Solution:

Differences between distillation, distillation under reduced pressure and steam distillation may be summarized as :

Criterion for difference	Distillation	Distillation under reduced pressure	Steam distillation
Used for	Separation of volatile liquids from non-volatile impurities.	Separation of liquids having very high boiling points or those, which decompose at or below their boiling points.	For a substances which are immiscible in water but are steam volatile.
Difference in b.p. of liquids involved	The liquids involved differ in their b.p. by 40-50°C.	-	The liquids separated by this method have very high b.p. e.g., Aniline has b.p. of 184°C.
Method	Simple heating of the mixture in a round bottom flask fitted with condenser allows the lower boiling liquid to be collected first and the higher boiling one is collected later.	Since, one of the component decomposes before reaching its boiling point the heating is carried out under reduced pressure so that boiling occurs at a lower temperature and the component is collected in pure form.	Mixture of steam and volatile organic compound is condensed and collected. The compound is separated from water using a separating funnel.
Example	A mixture of chloroform (b.p. 334 K and aniline b.p. 457 K).	Separation of glycerol from spent - lye in soap industry.	Separation of aniline from aniline - water mixture.

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