Question

Which of the following reagents can be used to distinguish between methanoic acid and ethanoic acid?
(A) Tollen’s reagent
(B) $ FeC{l_3} $ solution
(C) $ NaOH $ solution
(D) $ N{a_2}C{O_3} $ solution

Answer 1

Hint : Methanoic acid is $ HCOOH $ and ethanoic acid is $ C{H_3}COOH $ . Both have a double bond between carbon and oxygen and are carbonyl compounds. The Tollen’s reagent can react with a carbon having a double bond with oxygen and the carbon should also have a hydrogen atom attached to it.

Complete Step By Step Answer:
Tollen’s reagent will react with methanoic acid as there is a carbon bonded to a hydrogen atom and carbon also forms a double bond with oxygen. This reagent does not react with ethanoic acid because even though carbon is doubly bonded to oxygen, it does not have a hydrogen attached to it. $ N{a_2}C{O_3} $ solution is a basic solution. Both methanoic acid and ethanoic acid are acids. So, an acid base reaction takes place when the $ N{a_2}C{O_3} $ solution is used as a reagent. A salt and carbon dioxide are formed as products in this reaction. So, tollen’s reagent i.e. ammoniacal silver nitrate solution can be used to differentiate between methanoic acid and ethanoic acid. Tollen’s reagent can be reduced by methanoic acid but it is not reduced by ethanoic acid.
Therefore, option A is correct.

Note :
Tollen’s reagent is used in testing the presence of an aldehyde group or an alpha-hydroxy ketone functional group. This reagent generally consists of a solution of silver nitrate and ammonia. The structures containing an aldehyde give positive Tollens test. Tollen's reagent is a mild oxidising agent. This test is also called the silver mirror test. During this test, a silver mirror is formed because the silver ions present in the Tollen’s reagent are reduced into metallic silver.