Understanding the Concept:
Azeotropes are mixtures of two or more liquids that boil at a constant temperature and possess the same composition in both liquid and vapour phases. They are broadly classified into:
Minimum boiling azeotropes \(\rightarrow\) formed by positive deviation from Raoult’s law.
Maximum boiling azeotropes \(\rightarrow\) formed by negative deviation from Raoult’s law.
Step 1: Understanding maximum boiling azeotropes.
A maximum boiling azeotrope is formed when the intermolecular attractions between unlike molecules are stronger than those between like molecules. Due to these stronger attractions:
escaping tendency of molecules decreases,
vapour pressure decreases,
boiling point increases.
Thus, the solution boils at a temperature higher than either of the pure liquids.
Step 2: Analyzing acetone-chloroform system.
Acetone contains a carbonyl oxygen atom having lone pair of electrons, while chloroform contains a highly polarized hydrogen atom.
Strong hydrogen bonding occurs:
\[
(CH_3)_2CO \cdots H-CCl_3
\]
This strong interaction causes a large negative deviation from Raoult’s law.
Step 3: Comparing with other options.
Benzene-toluene behaves nearly ideally.
Ethanol-water forms a minimum boiling azeotrope due to positive deviation.
CS\(_2\)-acetone also shows positive deviation.
Therefore, acetone-chloroform forms a maximum boiling azeotrope.