What is Formic Acid: Its Structure, Properties and Uses

The Formic Acid Formula is HCOOH. It is commonly referred to as Methanoic acid, Formic acid, Aminic acid, and Hydrogen carboxylic acid. Formic acid is a colourless and fuming liquid with a pungent, acrid odour. JEE Main and NEET covers questions based on the properties of formic acid. Therefore, it is advisable to understand the application of the property. The following table briefly highlights the properties of formic acid:

The following table highlights the physical properties of formic acid. Aldehydes, Ketones and Carboxylic acid chapter covers these properties in more detail:

Let us take a look at the chemical properties of formic acid:

• Formic acid is 10 times stronger than acetic acid and reacts with bases to form salts.

        HCOOH   +   NaOH    →    HCOONa    +   H₂O 
(Formic Acid) (Sodium Hydroxide) (Sodium Formate)   (Water)

• It is a potent reducing agent because of the H-C=O arrangement in the molecule, and therefore, it can give away electrons in reactions.

  HCOOH  +  2Ag⁺(aq)  +  2OH⁻(aq)  →  2Ag(s)  +  CO₂(g)  +  2H₂O(l)
(Formic Acid)  (Silver Ions)  (Base)     (Solid Silver) (Carbon Dioxide) (Water)

• Formic acid is an unstable molecule that can decompose easily. For example, when it is heated with a catalyst like sulfuric acid, it will decompose into carbon monoxide and water.

                  H₂SO₄, Δ
  HCOOH      →          CO         +             H₂O
(Formic Acid)     (Carbon Monoxide)    (Water)

• It reacts with alcohol in a process called esterification, resulting in formate ester molecules. These molecules have a pleasant and fruity smell.

                                  H⁺ catalyst
  HCOOH      +    CH₃CH₂OH      ⇌      HCOOCH₂CH₃      +    H₂O
(Formic Acid)      (Ethanol)                (Ethyl Formate)           (Water)

The IUPAC name of Formic acid is Methanoic acid. The molecular formula is CH₂O₂, and the condensed formula is HCOOH.

    H

    |

H – C = O

    |

    O – H

• Here, the carbon is double-bonded to one oxygen (carbonyl) and single-bonded to another oxygen that carries an acidic proton.
• Carbon hybridisation: sp² → trigonal-planar around C, ~120° bond angles.
• Here, two hydrogens (formyl-H and acidic-H) sit on the opposite sides of the plane. 
• The C=O bond length is 1.21 Å and C–O single bond: ≈ 1.36 Å. O–H bond: ≈ 0.96 Å, which is almost colinear with the C-O single bond, which is effective for hydrogen bonding.

Formic acid is used for the following reasons:

• The vital use of formic acid is as a preservative and antibacterial agent in animal feed.
• In the poultry industry, formic acid is used to kill Salmonella bacteria.
•  It is also used as a reducing agent for reducing sodium and potassium dichromate.
• Formic acid is also used for the processing of organic latex into rubber. However, formic acid is the active ingredient in a few brands of household limescale remover.
• It is also used in a group of saturated monocarboxylic acids. It is worth noting that formic acid remains an essential ingredient in the dyeing and tanning industries.