Question

How formic acid and formaldehyde can be distinguished?

Answer 1

The number of carbon atoms in both formic acid and formaldehyde is one. The functional group in formic acid is –COOH and the functional group in formaldehyde is >C=O, so the formula of formic acid is HCOOH and the formula of formaldehyde is HCHO. Formic acid can liberate carbon dioxide but formaldehyde cannot liberate carbon dioxide.

Complete answer:
Most of the organic compounds look similar so, there are many tests done to distinguish them. So, we are given two compounds to be distinguished, i.e., formic acid and formaldehyde.
The number of carbon atoms in both formic acid and formaldehyde is one. Formic acid is a member of carboxylic acid and formaldehyde is a member of aldehyde. The functional group in formic acid is –COOH and the functional group in formaldehyde is >C=O, so the formula of formic acid is HCOOH and the formula of formaldehyde is HCHO.
So, the test which can be used to distinguish the formic acid and formaldehyde is the sodium bicarbonate test ($NaHC{{O}_{3}}$), because one of the compounds is acid.
When formic acid, i.e., HCOOH is treated with sodium bicarbonate, then there will be the liberation of carbon dioxide gas because it is an acid while when formaldehyde, i.e., HCHO is treated with sodium bicarbonate, then there will be no reaction because it is an aldehyde, not an acid.

Note:
Formaldehyde is a compound having a carbonyl group and the IUPAC name of formaldehyde is methanal and the IUPAC name of formic acid is methanoic acid. The basic test of distinguishing the acid is sodium bicarbonate.