JEE Main · 2019 · Shift-IImediumEC-040

The decreasing order of electrical conductivity of the following aqueous solutions is: (A) 0.1 M Formic acid, (B) 0.1 M…

Electrochemistry · Class 12 · JEE Main Previous Year Question

Question

The decreasing order of electrical conductivity of the following aqueous solutions is:

(A) 0.1 M Formic acid, (B) 0.1 M A\cetic acid, (C) 0.1 M Benzoic acid.

Options
  1. a

    (A) > (B) > (C)

  2. b

    (A) > (C) > (B)

  3. c

    (C) > (B) > (A)

  4. d

    (C) > (A) > (B)

Correct Answerb

(A) > (C) > (B)

Detailed Solution

Strategy: For weak acids of the same concentration, conductivity is proportional to the number of ions, which depends on the acid dissociation constant (KaK_a). Higher KaK_a \implies higher \degree of dissociation.

Comparison of Acid Strengths:

  1. Formic acid (A): The strongest among the three due to lack of bulky/donating groups. (Highest KaK_a)
  2. Benzoic acid (C): Intermediate strength.
  3. A\cetic acid (B): Weakest among the three because the \ceCH3\ce{-CH3} group is +I (inductive) and redu\ces acidity. (Lowest KaK_a)

Order of conductivity: A > C > B.

Answer: (b) (A) > (C) > (B)\boxed{\text{Answer: (b) (A) > (C) > (B)}}

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