Question

Methanoic acid and Ethanoic acid can be differentiated by:

• A. $\text{Fehling's test}$
• B. $\text{Iodoform test}$
• C. $\text{Tollens' reagent}$
• D. $NaHC{O}_3\text{test}$

Answer 1

Answer: (A), (C)

$\text{Tollens' reagent}$

Methanoic acid contains both aldehyde and carboxylic acid group while Ethanoic acid only contains carboxylic acid group.
(A) Fehlings test - Aldehydes respond to Fehling's test, but ketones and acid do not. Hence formic acid answers for Fehling test.

$HCOOH+4O{H}^{-}+2C{u}^{2+}\to C{O}_2+3H_{2}O+C{u}_{2}O$

(B) Iodoform test - Iodoform test is given by more reactive carbonyl group ketone or aldehyde that has $C{H}_{3}CO$ group.

(C) Formic acid can also answer Tollens reagent and oxidised to carbondioxide.

$HCOOH+2\left[Ag\right(N{H}_3{)}_2{]}^{+}+2O{H}^{-}\to 2Ag+C{O}_2+2H_{2}O+4N{H}_3$

(D) Both will answer sodium bicarbonate test and evolves $C{O}_2$.