Distinction between pairs of compounds
Pentanal `(CH_(3)CH_(2)CH_(2)CH_(2)CHO)` and diethyl ketone `(CH_(3)CH_(2)COCH_(2)CH_(3))`
(a) Fehling Solution test.
Tollens' reagent Test.

Explanation

Following tests help to distinguish these :
Pentanal reduces Fehling.s solution to `Cu_(2)O` (red ppt) while diethylketone does not give this test.
`CH_(3)CH_(2)CH_(2)CH_(2)CHO+underset("Fehling.s Solution")ubrace(2Cu^(2+)+)5OH^(-)`
`rarrundersetunderset(("red ppt."))("Cuprous oxide")(Cu_(2)Odarr+CH_(3)CH_(2))CH_(2)CH_(2)COO^(-)+3H_(2)O`
(b) Pentanal forms silver mirror with Tollens. reagent while diethylketone does not respond to this test.
`CH_(3)CH_(2)CH_(2)CH_(2)CHO+underset("Tollens. reagent")(2[Ag(NH_(3))_(2)]^(+))+3OH^(-)rarr`
`underset("Silver mirror")(2Agdarr)+CH_(3)CH_(2)CH_(2)CH_(2)COO^(-)+4NH_(3)+2H_(2)O`