Question

Which one of the following is the strongest acid?

• A. ${\mathrm{ClCH}}_2\mathrm{COOH}$
• B. ${\mathrm{BrCH}}_2\mathrm{COOH}$
• C. ${\mathrm{FCH}}_2\mathrm{COOH}$
• D. ${\mathrm{ICH}}_2\mathrm{COOH}$

Answer 1

The correct option is C

${\mathrm{FCH}}_2\mathrm{COOH}$

Explanation for the correct option:

(c ) ${\mathrm{FCH}}_2\mathrm{COOH}$

• Because most strong acids have ions in solution, the bonds that hold H and A together must be weak. Strong acids quickly divide into ions. Weak acids frequently exist as molecules with only a few ions in solution, so the bonds that connect H and A must be solid.
• Because the halogens' electron-withdrawing inductive action (-I effect) declines in the order $\mathrm{F}>\mathrm{Cl}>\mathrm{Br}>\mathrm{I}$,
• As a result, the acidity of the $\mathrm{\alpha }$ - halo acids decreases in the same order.
• ${\mathrm{FCH}}_2\mathrm{COOH}>{\mathrm{ClCH}}_2\mathrm{COOH}>{\mathrm{BrCH}}_2\mathrm{COOH}>{\mathrm{ICH}}_2\mathrm{COOH}$
• Hence this option is correct

Explanation for the incorrect options:

(a) ${\mathrm{ClCH}}_2\mathrm{COOH}$

• ${\mathrm{FCH}}_2\mathrm{COOH}$ is stronger acid than ${\mathrm{ClCH}}_2\mathrm{COOH}$
• Thus, this option is incorrect

(b)${\mathrm{BrCH}}_2\mathrm{COOH}$

• ${\mathrm{FCH}}_2\mathrm{COOH}$ , ${\mathrm{ClCH}}_2\mathrm{COOH}$ is stronger acid than ${\mathrm{BrCH}}_2\mathrm{COOH}$
• Thus, this option is incorrect

(d) ${\mathrm{ICH}}_2\mathrm{COOH}$

• ${\mathrm{FCH}}_2\mathrm{COOH}$ , ${\mathrm{ClCH}}_2\mathrm{COOH}$ , ${\mathrm{BrCH}}_2\mathrm{COOH}$ is stronger acid than ${\mathrm{ICH}}_2\mathrm{COOH}$
• Thus, this option is incorrect

Hence the correct option is (c ) ${\mathrm{FCH}}_2\mathrm{COOH}$