`1.22 g` of benzoic acid is dissolved in (i) 100g acetone `(K_(b)` for acetone `=1.7)` and (ii) 100 g benzene `(K_(b)` for benzene `= 2.6)`. The elevation in boiling points `T_(b)` is `0.17^(@)C` and `0.13^(@)C` respectively.
(a) What are the molecular weights of benzoic acid in both the solutions?
(b) What do you deduce out of it in terms of structure of benzoic acid?

Answer

(a)122,
(b) It means that benzonic acid remains as it is in acetone while it dimerises in benzene
`(##BSL_CHM_DS_E01_111_A01##)`

Explanation

`DeltaT_(b)=ixxK_(b)xx(W_("solute")xx1000)/(m_("solute")xxW_("solvent"))`
For solution of benzonic acid in acetone
`0.17=ixx1.7xx(1.22xx1000)/(122xx100)`
`i=1`
`therefore` benzonic acid does not dimerise in acetone
Now, for solution of benzonic acid in bezonic
`0.13=ixx2.6(1.22xx1000)/(122xx100)`
`i=1/2`
`i=1+((1)/(2)-1)alpha`
If we assume `alpha=100%`
`n=2`
`therefore` Benzonic acid dimerise in benzene.