Question

The correct order of decreasing acid strength of trichloroacetic acid (A), trifluoroacetic acid (B), acetic acid (C) and formic acid (D) is

• A. B > A > D > C
• B. B > D > C > A
• C. A > B > C > D
• D. A > C > B > D

Answer 1

The Correct Option is A

To determine the correct order of decreasing acid strength for the given acids, we need to analyze their chemical structures and the inductive effects of substituents.

1. Trifluoroacetic Acid (B): This compound has three highly electronegative fluorine atoms attached to the carbon nearest to the carboxylic acid group. The strong electron-withdrawing effect of fluorine increases the acidity by stabilizing the resultant carboxylate ion after dissociation. Thus, trifluoroacetic acid is very strong in acidity.
2. Trichloroacetic Acid (A): Like trifluoroacetic acid, trichloroacetic acid has three electronegative chlorine atoms, but chlorine is less electronegative than fluorine. Thus, while still a strong acid, it is less acidic than trifluoroacetic acid.
3. Formic Acid (D): Formic acid is stronger than acetic acid as it does not have any additional alkyl group (such as a methyl group) that can donate electron density to destabilize the resulting anion. The simple formyl group is less electron-donating than a methyl group.
4. Acetic Acid (C): Acetic acid has a methyl group, which is slightly electron-donating, making the release of a proton less favorable compared to formic acid. Thus, it is the weakest among the four.

Based on this analysis, the correct order of decreasing acid strength is: B > A > D > C.