Question

The reagent which distinguishes formic acid and acetic acid is

• A. 2,4-dinitrophenyl hydrazine
• B. HgCl$_2$
• C. C$_2$H$_5$ONa
• D. Hg$_2$Cl$_2$

Hint:

Formic acid behaves like aldehyde → shows reducing nature.

Answer 1

The Correct Option is B

To determine the reagent that can distinguish between formic acid (HCOOH) and acetic acid (CH₃COOH), we need to consider their chemical properties and reactions with different reagents.

Chemical Properties:

• Formic Acid (HCOOH): Unlike most carboxylic acids, formic acid has the unique ability to reduce metal ions due to its additional aldehyde group. This makes it capable of reducing reagents, such as mercuric chloride (HgCl₂), to metallic mercury or mercurous chloride (Hg₂Cl₂).
• Acetic Acid (CH₃COOH): As a typical carboxylic acid, it does not possess reducing properties and hence cannot reduce mercuric chloride.

Reagent Analysis:

• \(2,4\text{-dinitrophenyl hydrazine}\) is used to identify aldehydes and ketones, but both formic and acetic acids do not react with it.
• \(\text{HgCl}_{2}\) can be used to test for reducing agents. Formic acid will reduce \(\text{HgCl}_{2}\) to a white precipitate of \(\text{Hg}_{2}\text{Cl}_{2}\), whereas acetic acid will not.
• \(\text{C}_{2}\text{H}_{5}\text{ONa}\) is sodium ethoxide, a strong base but not useful for distinguishing these two acids.
• \(\text{Hg}_{2}\text{Cl}_{2}\) is not a reagent but rather a product of a reaction that involves \(\text{HgCl}_{2}\).

Conclusion: The correct reagent to distinguish between formic acid and acetic acid is \(\text{HgCl}_{2}\) because formic acid will react with it to form a precipitate of \(\text{Hg}_{2}\text{Cl}_{2}\), while acetic acid will not.