Question

Assertion : Benzoic acid is stronger acid than acetic acid.
Reason : $K_a$ for benzoic acid is $6.5 \times 10^{-5}$ and for acetic acid is $1.74 \times 10^{-5}$.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (A)

Acidic means - it depends $H +$ dissociation and the formation of conjugate anion.
$C _{6} H _{5}- COOH + H _{2} O \rightarrow C _{6} H _{5}- COO ^{-}+ H _{3} O ^{+}$
$CH _{3} COOH + H _{2} O \rightarrow CH _{3} COO ^{-}+ H _{3} O ^{+}$
In acetic acid, Methyl group is electron releasing group, so the formation of conjugate acetate anion is less when compare to benzoate anion.
Because phenyl is electron withdrawing group, it pulls the electron from carboxyl group. Ka value for benzoic acid is $6.5 \times 10^{-5}$ and for acetic acid is $1.74 \times 10^{-5}$.
Hence, Benzoic acid is more acidic than acetic acid.