Which of the following statements are correct about azeotropic mixtures?
A. They have the same composition in liquid and vapour phases.
B. They can be separated by fractional distillation
C. They are formed at a specific composition.
D. Solutions which show positive deviation from Raoult's law form maximum boiling azeotrope.
E. The azeotrope of ethanol and water is formed by \(80\%\) ethanol and \(20\%\) water.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A and C only
Azeotropes are binary mixtures with the same composition in liquid and vapour phase; they boil at a constant temperature, so their components cannot be separated by fractional distillation.
(A) Same composition in liquid and vapour phases — True. This defines an azeotrope.
(B) They can be separated by fractional distillation — False. The vapour has the same composition as the liquid, so distillation cannot separate them.
(C) They are formed at a specific composition — True. Large positive or negative deviation gives an azeotrope at one particular composition.
(D) Positive deviation forms a maximum boiling azeotrope — False. Positive deviation gives a minimum boiling azeotrope; negative deviation gives the maximum boiling one.
(E) Ethanol-water azeotrope is 80% ethanol and 20% water — False. It contains about 95% ethanol by volume.
NCERT (2026-27 edition):
Non-ideal Solutions – …
“… There are two types of azeotropes called minimum boiling azeotrope and maximum boiling azeotrope. The solutions which show a large positive deviation from Raoult’s law form minimum boiling azeotrope at a specific composition. … For example, ethanol-water mixture (obtained by fermentation of sugars) on fractional distillation gives a solution containing approximately 95% by volume of ethanol.”