How will you distinguish between:
(a) Formic acid and acetic acid.?
(b) Oxalic acid and acetic: acid?
(c) Succinic acid and oxalic acid?

Explanation

(a) (i) Formic acid produces silver mirror with ammoniacal silver nitrate solution. Acetic acid does not give this test.
`underset("Formic acid")(HCOOH)+underset("Tollens' reagent")(2Ag(NH_(3))_(2)NO_(3))tounderset("Silver mirror")(2Ag)+CO_(2)+2NH_(4)NO_(3)+2NH_(3)`
(ii) Formic acid forms a white precipitate with `HgCl_(2)` solution. Acetic acid does not respond to this test.
(b) (i) Oxalic acid when heated decomposes and evolves `CO_(2)`. The gas when passed through lime water forms a white precipitate.

Acetic acid does not give this test.
(ii) Oxalic acid acts as a reducing agent. The decolourisation or acidified `KMnO_(4)` solution occurs when oxalic acid is added to it and the solution is warmed. This test is also not given by acetic acid.

(iii) Oxalic acid is a solid while acetic acid is a liquid with characteristic odour.
( c) Both the chemical tests used in part (b) of this question can also be employed to make distinction between oxalic acid and ,succinic acid.