Solutions
6.0 Azotropes
6.0 Azotropes
These are binary mixture having same composition in liquid and vapour phase and boil at constant temperature like pure liquid. Azotropes behaves like a pure liquid. Components of azotropes cannot be separated by fractional distillation.
Note: When two liquids are mixed and boiled, both components of mixture vapourize but the more volatile component vapourize more. So for a solution there is no fixed boiling point. But two liquid at a specific concentration form a mixture in which both component boil such that overall mixture boil at a constant temperature, such mixture are azotropes.
There are two types of Azotropes:
1) Minimum boiling Azotrope:
The solution which shows large positive deviation from Raoult's law at a specific concentration are called minimum boiling azotropes. It means if two liquid are mixed then at a specific concentration their boiling point will be constant and this boiling point is minimum.
For example, if $40\% $ of $A$ and $60\% $ of $B$ forms a minimum boiling azotrope, then this mixture has lowest boiling point. If we mix $30\% $ of A and $70\% $ of $B$ or $50\% $ of $A$ and $50\% $ of $B$, boilng point of these solution will be more than minimum boiling azotropic mixture.
Examples of Min. boiling Azotrope: $95\% $ by volume of ethanol in water.
2) Maximum boiling Azotrope:
The solution which shows large negative deviation from Raoult's law at a specific concentration are called maximum boiling azotropes.
Examples: $68\% $ Nitric acid and $32\% $ water by mass.
