Question

Which of the following acid is the strongest acid?

• A. ${\mathrm{CH}}_3\mathrm{COOH}$
• B. $\mathrm{HCOOH}$
• C. ${\left({\mathrm{CH}}_3\right)}_3\mathrm{CCOOH}$
• D. ${\left({\mathrm{CH}}_3\right)}_2\mathrm{CHCOOH}$

Answer 1

The correct option is B

$\mathrm{HCOOH}$

Explanation for the correct option:

(B) $\mathrm{HCOOH}$

• The simplest carboxylic acid is formic acid, also known scientifically as methanoic acid.
• It has a chemical formula $\mathrm{HCOOH}$.
• It occurs naturally, most notably in certain ants.
• In the case of carboxylic acids, a positive inductive effect (+I-effect) is present due to the electron-donating tendency of alkyl groups.
• The +I effect increases with the presence of a higher number of alkyl groups. This +I effect reduces the acidity.
• In formic acid, there is no alkyl group present.
• Thus, formic acid is the strongest acid among acetic, propanoic, and pivalic acids.

Explanation for the incorrect options:

(A) ${\mathrm{CH}}_3\mathrm{COOH}$

• Acetic acid is officially known as ethanoic acid.
• It is an organic molecule with a chemical formula ${\mathrm{CH}}_3\mathrm{COOH}$ that is acidic and colorless.
• In acetic acid, one alkyl group is present, thus it is less acidic than formic acid due to +I effect.

(C) ${\left({\mathrm{CH}}_3\right)}_3\mathrm{CCOOH}$

• The chemical formula for pivalic acid is ${\left({\mathrm{CH}}_3\right)}_3{\mathrm{CCO}}_2\mathrm{H}$.
• Pivalic acid has more than one alkyl group present, thus it is less acidic than acetic acid due to more +I effect.

(D) ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CO}}_2\mathrm{H}$

• Propionic acid has a chemical formula ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CO}}_2\mathrm{H}$.
• Propionic acid has more than one alkyl group present, thus it is less acidic than acetic acid due to more +I effect.

Therefore, the correct option is (B) $\mathrm{HCOOH}$