Formic Acid or Methanoic Acid

Formic Acid

source : owlcation

Occurrence of formic acid:

Formic acid is an irritating chemical present in the sprayed venom of red ant  and in the secretion released from some stinging nettles like honey bee & wasp .

Laboratory Preparation:

HCOOH is prepared by heating a mixture of glycerol and crystalline oxalic acid at 110⁰ C. Glycerol mono oxalate is formed which  decomposes into glycerol monoformate and CO2. When the evolution of CO stops,  more oxalic acid is added, then  HCOOH is formed.

source : Aasanka Sample Content

Anhydrous Formic Acid : 

The distillate contains  HCOOH and water. Anhydrous formic acid  cannot be obtained from the distillate by fractional distillation as the boiling point of water (100 ⁰ C) and formic acid (100.5 ⁰C) are nearly equal.

The aqueous solution is neutralized by PbCO₃ and the solution on concentration gives crystals of lead formate which is filtered , dried and heated at 100 ⁰C in the current of H₂S. Anhydrous HCOOH is obtained which is contaminated with H₂S. It is mixed with some lead formate and distilled to obtain pure HCOOH.

2HCOOH + PbCO₃ ——-> (HCOO)₂Pb(lead formate) +H₂O +CO₂

(HCOO)₂Pb + H₂S ——->PbS (lead sulphide) +HCOOH

Physical properties :

1)  It is a colorless pungent smelling liquid.

2) It boils at 100.5 oC.

3) It is miscible with H2O, alcohol and ether.

4) It is strongly corrosive and causes blisters on skin.

5) It exists in aqueous solution as a dimer due to  H-bonding.

source : wikiland

Uses :

1. In the laboratory for preparation of Carbon dioxide .

2. In textile dying and finishing.

3. As a reducing agent.

4. In leather tanning.

source : SlideShare

Test of HCOOH :

1.  It turns blue litmus red.

2.Its aqueous solution gives effervescence with  sodium bicarbonate ( NaHCO₃) & sodium carbonate (Na₂CO₃) .

3.Its neutral solution gives  silver  mirror or black precipitate with tollen’s reagent

4. when heated with concentrated H₂SO₄, it evolves Carbon monoxide which burns with blue flame on the mouth of test tube.

5.It decolorises pink color of acidic potassium permanganate.

6. Neutral solution of formic acid gives red ppt. of cuprous oxide with fehling solution.

7.  Neutral solution of formic acid gives red ppt. with aqueous solution of ferric chloride.

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