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Degree of dissociation or Ka of a weak electrolyte from molar conductivity

This type of question, asked 4 times: 10 Apr 2023, 4 Apr 2025, 21 Jan 2026 S1, 24 Jan 2026 S2. All 4 questions below, oldest first.

Try each one first, then open its answer.

  1. Question 1

    10 Apr 2023

    149
    The specific conductance of 0.0025M0.0025M acetic acid is 5×10−5 S cm−15 \times10^{- 5}\text{ }S{\text{ }cm}^{- 1} at a certain temperature. The dissociation constant of acetic acid is____ 10−710^{- 7}. (Nearest integer) Consider limiting molar conductivity of CH3COOHCH_{3}COOH as 400 S cm2 mol−1400\text{ }S{\text{ }cm}^{2}{\text{ }mol}^{- 1}

  2. Question 2

    4 Apr 2025

    124
    The molar conductance of an infinitely dilute solution of ammonium chloride was found to be 185 S cm2 mol−1185\text{ }S{\text{ }cm}^{2}{\text{ }mol}^{- 1} and the ionic conductance of hydroxyl and chloride ions are 170 and 70 S cm2 mol−170\text{ }S{\text{ }cm}^{2}{\text{ }mol}^{- 1}, respectively. If molar conductance of 0.02 M solution of ammonium hydroxide is 85.5 S cm2 mol−185.5\text{ }S{\text{ }cm}^{2}{\text{ }mol}^{- 1}, its degree of dissociation is given by x×10−1x \times 10^{- 1}. The value of xx is ____\_\_\_\_. (Nearest integer)

  3. Question 3

    21 Jan 2026 S1

    47
    The pH and conductance of a weak acid (HX) was found to be 5 and 4×10−5 S4 \times 10^{- 5}\text{ }S, respectively. The conductance was measured under standard condition using a cell where the electrode plates having a surface area of 1 cm21{\text{ }cm}^{2} were at a distance of 15 cm apart. The value of the limiting molar conductivity is ____\_\_\_\_ Sm2 mol−1Sm^{2}{\text{ }mol}^{- 1}. (nearest integer) (Given: degree of dissociation of the weak acid (a) << 1)

  4. Question 4

    24 Jan 2026 S2

    49
    Molar conductivity of a weak acid HQ of concentration 0.18 M was found to be 1/301/30 of the molar conductivity of another weak acid HZ with concentration of 0.02 M. If λQ−0\lambda_{Q^{-}}^{0} happened to be equal with λZ−0\lambda_{Z^{-}}^{0}, then the difference of the pKa{pK}_{a} values of the two weak acids (pKa(HQ)−pKa(HZ))\left( {pK}_{a}(HQ) - {pK}_{a}(HZ) \right) is ____\_\_\_\_ (Nearest integer). [Given : degree of dissociation (α)≪1(\alpha) \ll 1 for both weak acids, λ∘\lambda^{\circ} : limiting molar conductivity of ions]