Question

“Formic acid behaves both as an aldehyde and an acid.” Explain.

Hint:

Formic acid = HCOOH = only carboxylic acid with aldehydic character. Reduces Tollen’s reagent just like HCHO.

Answer 1

Step 1: Explanation.
Formic acid (HCOOH) is unique because it contains both the –CHO (aldehyde group) and the –COOH (carboxylic acid group). Hence, it exhibits the properties of both aldehydes and acids.
Step 2: Aldehydic nature.
Formic acid gives reactions typical of aldehydes such as:
- (i) Reducing nature: It reduces Tollen’s reagent and Fehling’s solution.
\[ \text{HCOOH} + 2[\text{Ag(NH}_3)_2]^+ + \text{OH}^- \rightarrow 2\text{Ag} + \text{CO}_2 + 3\text{NH}_3 + 2\text{H}_2\text{O} \] Step 3: Acidic nature.
Formic acid also behaves as a typical carboxylic acid:
- It reacts with metals to liberate hydrogen gas.
\[ \text{2HCOOH} + \text{Zn} \rightarrow (\text{HCOO})_2\text{Zn} + \text{H}_2 \] - It neutralizes alkalis to form formates.
Step 4: Conclusion.
Thus, due to the presence of both aldehyde and acid functional groups, formic acid exhibits dual behavior — reducing like an aldehyde and acidic like a carboxylic acid.