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) .
