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1.22 g of benzoic acid is dissolved in (...

`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?

Text Solution

Verified by Experts

The correct Answer is:
(a) 122, (b) It means that benzoic acid remains as it is in acetone while it dimerises in benzene
`(##ALN_CHM_C08_E01_613_A01##)`
(a) (i) `DeltaT_(b) = iK_(b).m`
`0.17 = ixx 1.7 xx (1.22//122)/(0.1)`
`L = 1 = ((mol ut)_(Th))/((mol ut)_(ACt))`
`(mol ut)_(ACt) = (122)/(1) gm//mol`
(ii) `DeltaT_(b) = ixx K_(b).m`
`0.13 = ixx 2.6 xx (1.22//122)/(0.1)`
`i=0.5 = ((mol ut)_(Th))/((mol ut)_(ACt)) rArr (mol ut)_(Act) = (122)/(0.5)`
`= 244 gm//mol`
(b) In Acetone its normal ie but in benzene it is in dimenc form

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