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  4. Benzoic acid and carbolic acid can be distinguished By:

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Q. Benzoic acid and carbolic acid can be distinguished By:

Redox Reactions

Solution:

a. Phenol is also called carbolic acid
Benzoic acid is more acidic than phenol. So the acid reacts with $NaHCO _3$ to give $CO _2( g )$, while phenol does not react
b. Acids give buff-coloured precipitate with neutral $FeCl _3$, while phenol gives violet colouration with neutral $FeCl _3$ solution, e.g.,
$3 PhCOOH + FeCl _3 \rightarrow( PhCOO )_3 Fe +3 HCl$
(Ferric benzoate)(Buff coloured ppt.)
$3 PhOH + FeCl _3 \rightarrow( PhO )_3 Fe +3 HCl$
(Ferric Phenoxide)(Violet colouration)
c. Both acid and phenol react with aqueous $NaOH$ to give their corresponding salts
$PhCOOH + NaOH \rightarrow PhCOONa$
$PhOH + NaOH \rightarrow PhONa$
d. Both acid and phenol react with $NH _3$
$PhCOOH + NH _3 \rightarrow PhCONH _2$ (Benzamide)$+ H _2 O$
$PhOH + NH _3 \rightarrow PhNH _2$ (Aniline) $+ H _2 O$
So the answers are (a) and (b)