Question

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

Answer 1

Acetic acid undergoes dimerisation, when dissolved in benzene.

Molecular mass of acetic acid is found 120.

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Answer 2

Given:

The degree of association, α = 30% = 0.3

To Find:

The observed molecular mass of acetic acid in benzene.

Calculation:

- For dimerisation, n = 2

- For association, we know that:

α = n (1 - i) / (n - 1)

⇒ 0.3 = 2 (1 - i) / (2 - 1)

⇒ 1 - i = 0.15

⇒ i = 0.85

- Again, we know that:

i = Normal molecular mass/ Abnormal molecular mass

⇒ 0.85 = 60/ Abnormal molecular mass

⇒ Abnormal molecular mass = 60/0.85

⇒ Abnormal molecular mass = 70.59 gm

- So, the observed molecular mass of acetic acid in benzene in the given conditions is 70.59 gm.