Question

Arrange the following acids in increasing order of their acidic strengths: HCOOH, FCH₂COOH, NO₂CH₂COOH, ClCH₂COOH

• A. HCOOH $<$FCH$_2$COOH$<$ NO$_2$CH$_2$COOH $<$ClCH$_2$COOH
• B. HCOOH $<$ NO$_2$CH$_2$COOH $<$ ClCH$_2$COOH $<$ FCH$_2$COOH
• C. NO$_2$CH$_2$COOH $<$ HCOOH $<$ ClCH$_2$COOH $<$ FCH$_2$COOH
• D. HCOOH $<$ ClCH$_2$COOH $<$ FCH$_2$COOH $<$ NO$_2$CH$_2$COOH

Answer 1

The Correct Option is D

To arrange the acids in increasing order of their acidic strengths, we need to consider the inductive effect of the substituents attached to the carboxylic acid group.

The acidic strength of a carboxylic acid is influenced by the electron-withdrawing or electron-donating nature of the substituents. Electron-withdrawing groups stabilize the carboxylate anion by dispersing the negative charge, thus increasing the acidity. Electron-donating groups destabilize the carboxylate anion, decreasing the acidity.

Let's analyze the given acids:

HCOOH (Formic acid): No electron-withdrawing group.

FCH₂COOH (Fluoroacetic acid): Fluorine is a highly electronegative and electron-withdrawing group.

NO₂CH₂COOH (Nitroacetic acid): The nitro group (NO₂) is a strong electron-withdrawing group.

ClCH₂COOH (Chloroacetic acid): Chlorine is an electronegative and electron-withdrawing group, but less so than fluorine or the nitro group.

The electron-withdrawing power of the substituents follows the order:

NO₂ > F > Cl > H

Therefore, the acidic strength will follow the same order:

NO₂CH₂COOH > FCH₂COOH > ClCH₂COOH > HCOOH

So, the increasing order of acidic strength is:

HCOOH < ClCH₂COOH < FCH₂COOH < NO₂CH₂COOH

The correct answer is:

Option 4: HCOOH < ClCH₂COOH < FCH₂COOH < NO₂CH₂COOH