Question

Explain why reducing property among carboxylic acids, formic acid (Methanoic acid) is the only acid that acts as reducing agent.
It reduces, acidified KMnO4 to MnSO4 , HgCl2 to Hg, Tollen’s reagent to silver mirror and Fehling’s solution to red ppt. and itself gets oxidised to CO2 and H2O.

Answer 1

Answer:

Explanation:

Hi,

Here is the answer to your question:

formic acid/methanoicacid is unique amongst simple carboxylic acids since it contains a hydrogen atom instead of an alkyl group(H-COOH,all other carboxylic acid contains an alkyl group attached to C instead of hydrogen on left side) ....thus formic acid may be regarded both as an aldehyde as well as a carboxylic acid..like aldehydes it can be easily oxidised to carbonic acid (H2CO3) which decomposes to give CO2 and H2O..  

HCOOH + [O] -----> [H2CO3] ----> CO2 + H2O  

thus like aldehydes it reduces Fehling's solution to red ppt. of Cu2O.....Tollen's reagent to silver mirror..  

Remember, methanoic acid is H-CO-OH.  Although the -CO-OH side makes it a carboxylic acid, it has a little bit of aldehyde character from the H-CO side.  As such, it can further be oxidized.  For example:

HCOOH + 2 Ag+  --->  CO2 + 2 Ag + 2 H+

Preparations for both Fehling's solution and Tollen's solution are available on Wikipedia (and perhaps in your textbook :-).  Both reactions are performed at room temperature and at atmospheric pressure.  Make sure not to store Tollen's solution long term as it eventually forms an explosive compound if left standing too long.