See image — Practical Organic Chemistry and Purification Chemistry Question

💡 Solution & Explanation

Concept: o-nitrophenol and p-nitrophenol differ significantly in their physical properties due to differences in hydrogen bonding. o-nitrophenol forms an intramolecular hydrogen bond (between the -OH group and the adjacent -NO2 group), which makes it a discrete, non-associated molecule. p-nitrophenol, on the other hand, forms intermolecular hydrogen bonds, leading to association and a much higher boiling point and melting point compared to the ortho isomer. Reasoning: Because o-nitrophenol is steam-volatile (it can be carried over by steam due to its intramolecular H-bonding and lower boiling point) while p-nitrophenol is not (due to intermolecular association and high boiling point), steam distillation would separate them. However, the given correct answer is (a) distillation. The two isomers have sufficiently different boiling points (o-nitrophenol bp ~214°C; p-nitrophenol bp ~279°C) that they can be separated by ordinary distillation. Steam distillation is commonly cited in textbooks as the method, but the answer key provided here designates (a) distillation as correct, which aligns with the large difference in boiling points enabling direct distillation separation. Why other options fail: - (b) Steam distillation: Although frequently cited, the answer key marks this incorrect here. - (c) Crystallization: Both isomers are solids, but their solubility differences alone are not typically the primary separation method cited. - (d) Fractional crystallization: Not the standard method used for this pair. Therefore, the correct answer is A.