The molar conductivities at infinite dilution of barium chloride, sulphuric acid and hydrochloric acid are 280, 860 and $426 \mathrm{Scm}^{2} \mathrm{~mol}^{-1}$ respectively. The molar conductivity at infinite dilution of barium sulphate is ______ $\mathrm{S} \mathrm{cm} \mathrm{mol}^{-1}$. (Round off to the nearest integer).

JEE Main · 2021 · 18 Mar 2021 · Shift 2 · Redox Reactions and Electrochemistry

The molar conductivities at infinite dilution of barium chloride, sulphuric acid and hydrochloric acid are 280, 860 and

426 Scm^{2} mol^{- 1}

respectively. The molar conductivity at infinite dilution of barium sulphate is ______

S cm mol^{- 1}

.
(Round off to the nearest integer).

Answer: 288

Solution

Kohlrausch's law makes limiting molar conductivities additive in the ions, so barium sulphate can be assembled from the three measured electrolytes. The combination

BaC l_{2} + H_{2} S O_{4} - 2 HCl

cancels both chloride ions and both hydrogen ions and leaves one

B a^{2 +}

with one

S O_{4}^{2 -}

, so

Λ_{m}^{\circ} (BaS O_{4}) = Λ_{m}^{\circ} (BaC l_{2}) + Λ_{m}^{\circ} (H_{2} S O_{4}) - 2 Λ_{m}^{\circ} (HCl) = 280 + 860 - 2 (426) = 288

The limiting molar conductivity of barium sulphate is

288 S c m^{2} mo l^{- 1}

JEE Main · 2021 · 18 Mar 2021 · Shift 2 · Integer answer

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JEE Main · 2021 · 18 Mar 2021 · Shift 2 · Redox Reactions and Electrochemistry

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