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Formic acid : properties

formic acid

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Chemical properties of formic acid :

HCOOH is the strongest acid among all the members of homologous series.

1. Acidic Nature:

a) It is monobasic acid. Its acidic properties are due to its ionization in aqueous solution.

HCOOH —> HCOO + H+

b) It reacts with metal carbonates and bicarbonates and evolve CO2.

HCOOH + NaHCO3 ——-> HCOONa +H2O + CO2

2 HCOOH + Na2CO3 ——-> 2 HCOONa + 2 H2O + CO2

c) It reacts with alkalies to form corresponding salts.

HCOOH + NaOH ——-> HCOONa +H2O

HCOOH +NH4OH ——-> HCOONH4 +H2O

d) Highly electropositive metals evolve H2 when react with HCOOH.

2 HCOOH + 2 Na ——–> 2 HCOONa + H2

e) It combines with alcohol to form ester.

HCOOH + CH3OH —–> HCOOCH3 (Methyl formate) + H2O

f) It reacts with PCl5 or SOCl2 to give formyl chloride which is not a stable compound. It decomposes into Hydrochloric acid  &  Carbon monoxide.

HCOOH + PCl5 ——-> HCOCl + POCl3 +HCl

HCOCl ——> HCl+ CO

HCOOH + SOCl2 ——-> HCOCl + SO2+HCl

HCOCl ——> HCl+ CO

2. Action of Heat :

when heated above 160 0 C, it decomposes to give  Carbon dioxide and Hydrogen.

HCOOH ——-> CO2+ H2

3. Dehydration :

when formic acid is warmed with concentrated H2SO4. It decomposes to give Carbon monoxide & water.

HCOOH ——–> CO + H2O

4. Action of heat on formates :

a) When Na-formate is heated to 36O 0C, it decomposes to form Sodium oxalate and Hydrogen .

2 HCOONa ——> (COONa)2  (sodium oxalate) + H2

b) When sodium-formate is heated with soda lime then Hydrogen gas is formed.

HCOONa +NaOH (CaO) ——-> H2 + Na2CO3

c) Formaldehyde  is formed when dry Ca-formate is heated.

d) Formamide is formed when ammonia formate is heated.

HCOONH4 ——-> HCONH2 + H2O

5) Reducing Properties:

Like aldehydes, formic acid behaves as reducing agent it is oxidized to  carbonic acid (unstable acid ), which decomposes into Carbon dioxide  and water.

HCOOH——> H2CO3 (unstable acid) ——> CO2 +H2O

a) It decolorizes acidified KMnO4 solution :

2KMnO4 + 3H2SO4 ——> K2SO4 + 2MnSO4 + 3H2O + 5(O)

HCOOH + O ——–> CO2 + H2O ]x 5

5 HCOOH + 2KMnO4 + 3H2SO4    ——> K2SO4 + 2MnSO4 + 8H2O +5CO2

b) It reduces mercuric chloride ( HgCl2 ) to white precipitate of mercurous chloride ( Hg2Cl2) and then grey precipitate of mercury (Hg) :

HCOOH + 2HgCl2 ——-> Hg2Cl2 + CO2 + 2HCl

2 HCOOH +Hg2Cl2 ——> 2Hg + 2CO2 + 2HCl

c) It reduces ammonical  AgNO3  (Tollen’s reagent)

HCOOH + Ag2O ——> CO2 + H2O + 2Ag

d) It reduces Fehling solution i.e gives red precipitate of  cuprous oxide (Cu2O) :

HCOOH + 2CuO —-> Cu2O( red ppt of cuprous oxide) + H2O+ CO2

Saroj Bhatia: Dr. Saroj Bhatia is an Ph.D in chemistry who has been teaching chemistry for over a decade. Currently she is a respected principal of a renowned college in her hometown. She took this medium for online users. Her proudest achievement is helping people learn chemistry.
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