Question

Which of the following are correct about the mixture of two miscible liquids forming azeotropes? This question has multiple correct options .
A) Has the lowest temperature at which the two liquids can exist in the liquid state .
B) Has the lowest temperature attainable at which two liquids form eutectic mixture .
C) Eutectic point has found application to attain low melting point solids which are eutectic mixtures.
D) Composition of azeotrope and their b.pt. vary with the external pressure.

Answer 1

An azeotropic mixture is a constant boiling mixture. The composition of an azeotropic mixture remains the same during boiling.

Complete answer:
For a binary mixture Eutectic point gives the lowest temperature at which a liquid can exist. At this point, the maximum number of allowable phases are in equilibrium. At this point, temperature remains constant until one phase disappears.
Few solutions follow Raoult’s law and show ideal behavior. Most of the solutions show either positive deviation or negative deviation from Raoult’s law. When a solution shows positive deviation from Raoult’s law, at a particular composition, total vapour pressure has maximum value. At this point, the solution has the lowest boiling point. When a solution shows negative deviation from Raoult’s law, at a particular composition, total vapour pressure has minimum value. At this point, the solution has the highest boiling point.
The composition is the same in liquid phase and vapour phase. You can vaporize the solution without any composition change. Such a solution behaves as pure liquid. This solution, that boils at constant temperature and behaves as a pure liquid, and has the same composition in liquid phase and vapour phase is known as an azeotropic mixture.
Minimum boiling azeotrope is formed by solutions showing positive deviation from Raoult’s law. Ethanol water mixture shows large negative deviation from Raoult’s law. 95% ethanol 5% water (by volume) mixture is the minimum boiling mixture. You cannot separate the components of an azeotropic mixture by using simple distillation.
68% nitric acid and 32% water (by mass) forms a solution that shows negative deviation from Raoult’s law. This solution has a maximum boiling azeotrope.

Hence, all the four options are the correct options.

Note: To separate azeotropic mixture, you can use azeotropic distillation. You add a third component that forms an azeotrope with one of the components. The remaining component has different boiling points and can be separated.