JEE Advanced 2023 — Paper 1 — CHEM-III solution

JEE Advanced2023Paper 1CHEM-III

The stoichiometric reaction of $516$ g of dimethyldichlorosilane with water results in a tetrameric cyclic product X in $75%$ yield. The weight (in g) of X obtained is ___.

[Use, molar mass (g mol $^{- 1}$ ): H = 1, C = 12, O = 16, Si = 28, Cl = 35.5]

Your answer

Solution

Balanced hydrolysis. Four molecules of $(CH_{3})_{2} SiCl_{2}$ react with four molecules of water to form the cyclic tetramer (octamethylcyclotetrasiloxane):

$4 (CH_{3})_{2} SiCl_{2} + 4 H_{2} O ⟶ [(CH_{3})_{2} SiO]_{4} + 8 HCl .$

Moles of silane. Molar mass of $(CH_{3})_{2} SiCl_{2}$ = $2 (12 + 3) + 28 + 2 (35.5) = 30 + 28 + 71 = 129$ g/mol. Moles available $= 516/129 = 4$ mol.

Theoretical mass of X. The stoichiometry gives $4/4 = 1$ mol of the tetramer. Molar mass of $[(CH_{3})_{2} SiO]_{4} = 4 (28 + 16 + 30) = 4 \times 74 = 296$ g/mol. Theoretical mass $= 296$ g.

Apply the yield. Actual mass $= 296 \times 0.75 = 222$ g.

Answer: 222.

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