A sample of 4 . 5mg of an unknown monohydric alcohol, R - OH was...

Alcohols on reaction with Grignard reagent forms hydrocarbons.This is due to the presence of active hydrogen in alcohols and here grignard reagent acts as a base.

When any alcohol is treated with methyl magnemsium iodide the hydrocarbon formed should be methane gas.

$ROH + {CH}_{3}MgI \to ROMgI + {CH}_{4}\left(g\right)$

Number of moles of ${CH}_{4} =$ Number of moles of $ROH$

$⇒ \dfrac{Volume ( Litres ) ofthegas}{22400} = \dfrac{massofthegas}{Molecularmassofthegas}$ (Assuming $NTP$ Condition)

$⇒ \dfrac{3 . 1}{22400} = \dfrac{4 . 5 \times {10}^{- 3}}{Molecularmassofthegas}$

$⇒ MM = 32 . 51$

$= 33$$g / mol$