Question

Acetic acid dimerises to an extent of 30% in benzene. the observed moleculer mass is ​

Answer 1

Given : Acetic acid dimerizes to an extent of 30% in benzene.

To find : The observed molecular mass of Acetic acid.

solution : 2(Acetic acid) ⇔(Acetic acid)₂

1 - α α/2

so, Van't Hoff factor, i = 1 - α + α/2 = 1 - α/2

we know, i = Theoretical Mol wt./Observed Mol wt.

we know, Theoretical Mol wt. of acetic acid = 60 g/mol

and α = 30% = 0.3

⇒1 - α/2 = 60/observed mol wt.

⇒1 - 0.3/2 = 60/Observed Mol wt.

⇒Observed Mol wt. = 60/0.85 = 70.6 g/mol

Therefore observed Mol weight of acetic acid is 70.6 g/mol.