JEE Main · 2023 · 25 Jan 2023 · Shift 1 · p-Block Elements

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Reaction of thionyl chloride with white phosphorus forms a compound [A], which on hydrolysis gives [B], a dibasic acid. [A] and [B] are respectively

(A) $P_{4} O_{6}$ and $H_{3} PO_{3}$
(B) $PCl_{3}$ and $H_{3} PO_{3}$ ✓ Correct
(C) $PCl_{5}$ and $H_{3} PO_{4}$
(D) $POCl_{3}$ and $H_{3} PO_{4}$

Answer: (B)

Solution

White phosphorus reacts with thionyl chloride to give phosphorus trichloride,

P X_{4} + 8 SOCl X_{2} 4 PCl X_{3} + 4 SO X_{2} + 2 S X_{2} Cl X_{2}

, so the first product is phosphorus trichloride. Its hydrolysis yields phosphorous acid,

PCl X_{3} + 3 H X_{2} O H X_{3} PO X_{3} + 3 HCl

. Although phosphorous acid holds three hydrogens, one is bonded directly to phosphorus and cannot ionise, leaving two acidic hydrogens, which makes it dibasic. The two compounds are phosphorus trichloride and phosphorous acid.

JEE Main · 2023 · 25 Jan 2023 · Shift 1 · Single correct option

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JEE Main · 2023 · 25 Jan 2023 · Shift 1 · p-Block Elements

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