▶️ Answer/Explanation
(a)
Explanation: Phenol (\(C_6H_5OH\)) is more acidic than water because the lone pair of electrons on the oxygen atom is delocalized into the aromatic ring. This delocalization stabilizes the phenoxide ion (\(C_6H_5O^-\)) formed after proton loss, making the O-H bond weaker and easier to break compared to water.
(b)(i) 2,4,6-tribromophenol and hydrogen bromide (HBr).
Explanation: When phenol reacts with excess bromine water, electrophilic aromatic substitution occurs at the 2, 4, and 6 positions (ortho and para to the -OH group) forming 2,4,6-tribromophenol (a white precipitate) and HBr as a byproduct.
(b)(ii)
Explanation: Nitration of phenol at room temperature produces two structural isomers: 2-nitrophenol (ortho-) and 4-nitrophenol (para-), both with molecular mass 139. The meta- product is not favored due to the directing effect of the -OH group.
(b)(iii) \(2C_6H_5OH + 2Na \rightarrow 2C_6H_5ONa + H_2\)
Explanation: Phenol reacts with sodium metal similarly to alcohols, forming sodium phenoxide (\(C_6H_5ONa\)) and hydrogen gas. The -OH group’s hydrogen is replaced by sodium.
(c)
Step 1: Reagents – Sodium nitrite (NaNO₂) and dilute hydrochloric acid (HCl). Conditions – Temperature maintained between 0-5°C.
Step 2: Reagents – Water (H₂O). Conditions – Heating under reflux.
Explanation: In step 1, phenylamine undergoes diazotization with NaNO₂/HCl at low temperatures to form a benzene diazonium salt. In step 2, this salt is hydrolyzed by heating with water to produce phenol, with nitrogen gas evolved as a byproduct.