Question

0.03 g of an alcohol R-OH was added to C2H5MgI the gas evolved measured 11.2 cc at STP.what is molecular mass of alcohol ?

Answer 1

R-OH + C₂H₅MgI → C₂H₅ – R + Mg(OH)I

alcohol gas

11.2 cc (11.2 x 10^-3 L) at STP means 0.5 x 10^-3 mole of gas

According to the equation:

Since 1 mole of gas is produced from 1 mole of alcohol

So, 0.5 x 10^-3 mole of gas will be produced by 0.5 x 10^-3 mole of alcohol

Given amount of alcohol = 0.3 g

This means 0.5 x 10^-3 mole of alcohol weighs 0.03 g

So 1 mole of alcohol weighs 0.03/0.5 x 10^-3 = 60 g/mol

Hence, the molecular mass of alcohol is 60