Distinction between pairs of compounds
Benzoic acid `(C_(6)H_(5)COOH)` and Phenol `(C_(6)H_(5)OH)`
(a) `FeCl_(3)` test.
(b) `NaHCO_(3)` test.

Explanation

Following tests help to distinguish these :
(a) Phenol gives violet colour with neutral `FeCl_(3)` solution while benzoic acid gives buff coloured ppt.
`underset("Phenol")(3C_(6)H_(5)OH)+FeCl_(3)rarrunderset(("Violet colour"))((C_(6)H_(5)O)_(3)Fe)+3HCl`
`underset("Benzoic acid")(3C_(6)H_(5)COOH)+FeCl_(3)rarrunderset("Buff coloured ppt")(Fe(C_(6)H_(5)COO)_(3))+3HCl`
(b) Benzoic acid gives `CO_(2)` gas with `Na HCO_(3)` while phenol does not.
`underset("Benzoic acid")(C_(6)H_(5)COOH)+NaHCO_(3)rarrunderset("Sod. benzoate")(C_(6)H_(5)COONa)+CO_(2)uarr+H_(2)O`