The pH and conductance of a weak acid (HX) was found to be 5 and 4 × 10S, respectively. The conductance was measured under standard condition using a cell where the electrode plates having a surface area of 1 cm² were at

Question

The pH and conductance of a weak acid (HX) was found to be 5 and $4 \times 10^{- 5} S$ respectively. The conductance was measured under standard condition using a cell where the electrode plates having a surface area of $1 {cm}^{2}$ were at a distance of 15 cm apart. The value of the limiting molar conductivity is ______ ${S m}^{2} {mol}^{- 1}$ . (nearest integer)
(Given : degree of dissociation of the weak acid $(α) ≪ 1)$ [2026]

Smart Achievers · Accepted Answer

(6)

$pH = 5$

$[H^{+}] = 10^{- 5} = [HX] . α$

$= [HX] \cdot \frac{Λ_{m}}{Λ_{m}^{\infty}}$

$Λ_{m} = \frac{k \times 1000}{[HX]}$

$K = G \cdot G^{*} = 4 \times 10^{- 5} \times \frac{15}{1} = 6 \times 10^{- 4} S . {cm}^{- 1}$

$[H^{+}] = 10^{- 5} = [HX] \times \frac{6 \times 10^{- 4} \times 1000}{Λ_{m}^{\infty} \times [HX]}$

$Λ_{m}^{\infty} = 60000 {S.cm}^{2} {mol}^{- 1}$

$Λ_{m}^{\infty} = 6 {S.m}^{2} {mol}^{- 1}$

Solution

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Solution

Ans. (6) pH=5 [H+]=10-5=[HX].α =[HX]·ΛmΛm∞ Λm=k×1000[HX] K=G·G*=4×10-5×151=6×10-4S.cm-1 [H+]=10-5=[HX]×6×10-4×1000Λm∞×[HX] Λm∞=60000 S.cm2 mol-1 Λm∞=6 S.m2 mol-1

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