JEE Main · 2022 · 25 Jul 2022 · Shift 2 · Some Basic Concepts of Chemistry

A sample of 4.5 mg of an unknown monohydric alcohol,

R - OH

was added to methylmagnesium iodide. A gas is evolved and is collected and its volume measured to be 3.1 mL. The molecular weight of the unknown alcohol is ____ g/mol. [Nearest integer]

Answer: 33

Solution

The reaction is:

ROH + CH_{3} MgI \to ROMgI + CH_{4} (g)

Moles of

CH_{4}

evolved = moles of ROH.

Assuming NTP conditions (22.4 L/mol):

\frac{V}{22400} = \frac{m}{M}

\frac{3.1}{22400} = \frac{4.5 \times 1 0 ^{- 3}}{M}

M = \frac{4.5 \times 1 0 ^{- 3} \times 22400}{3.1} = 32.51 g/mol

Nearest integer = 33 g/mol.

JEE Main · 2022 · 25 Jul 2022 · Shift 2 · Integer answer

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