Question

Assertion: Ortho and para-nitrophenol can be separated by steam distillation.

Reason: Para-nitrophenol is steam volatile due to intramolecular hydrogen bonding.

• A. Both assertion and reason are true and reason is the correct explanation of assertion.
• B. Both assertion and reason are true but reason is not the correct explanation of assertion.
• C. Assertion is true but reason is false.
• D. Both assertion and reason are false.

Answer 1

The correct option is C

Assertion is true but reason is false.

The explanation for the Assertion statement

• Steam distillation is a method for separating compounds that are volatile in steam, immiscible with water, and have a high vapor pressure at the water's boiling point.
• The hydroxyl group $(-\mathrm{OH})$ and nitrogen are in close proximity in $o$-nitrophenol.
• The hydrogen atoms attached to the oxygen establish a hydrogen bond.
• It forms intramolecular hydrogen bonding.
• Since and in the hydroxyl group of $p$-nitro phenol are relatively far apart, intramolecular hydrogen bonding cannot be formed between the hydrogen attached to the oxygen in the hydroxyl group.
• The $p$-nitro phenol form intermolecular hydrogen bonding.
• Hence $p$-nitrophenol is not steam distillable and $o$-nitrophenol is steam distillable.
• Therefore, $p$-nitrophenol and $o$-nitrophenol can be separated by steam distillation.

The explanation for the Reason statement

• Hydrogen bonding is the term for the electrostatic attraction between hydrogen and the second row's most electronegative elements.
• There are two types of hydrogen bonding: intra- and intermolecular.
• The intramolecular hydrogen bonding causes a decrease in water solubility and an increase in volatility.
• Therefore, $o$-nitrophenol is volatile.
• As $p$-nitrophenol undergoes association due to intermolecular hydrogen bonding, its molecular weight increases and its volatility decreases.
• Therefore, $p$-nitrophenol is non-volatile.

Therefore, the correct option is (C) Assertion is true but reason is false.