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JEE Advanced 2023Paper 1
Exam
JEE Advanced
Year
2023
Paper
Paper 1
Subject
Chemistry
Chapter
Electrochemistry

JEE Advanced 2023 · Paper 1 · Chemistry · Electrochemistry

Plotting 1 / Λ _ m against cΛ _ m for aqueous solutions of a...

Plotting 1/Λm1 / {Λ}_{m} against cΛm{cΛ}_{m} for aqueous solutions of a monobasic weak acid (HX)( HX ) resulted in a straight line with y−y -axis intercept of PP and slope of SS. The ratio P/SP / S is
\left[{Λ}_{m} =\right\text{molar conductivity}</p><p></p><p>{Λ}_{m}^{o} = limitingmolar conductivity c = molar concentration</p><p>Ka=dissociation constant ofHX]</p><p>{K}_{a} = \text{dissociation constant of}HX]

Options

  1. AKaΛmo{K}_{a}{Λ}_{m}^{o}
  2. BKaΛmo/2{K}_{a}{Λ}_{m}^{o} / 2
  3. C2KaΛmo2{K}_{a}{Λ}_{m}^{o}
  4. D1/(KaΛmo)1 / \left({K}_{a}{Λ}_{m}^{o}\right)

Correct answer

A. KaΛmo{K}_{a}{Λ}_{m}^{o}

Step-by-step solution

The degree of dissociation is the ratio of molar conductivity to the limiting molar conductivity.

α=ΛmΛmo\alpha = {Λ}_{m}{Λ}_{m}^{o}

The equilibrium reaction is given below,

HX⇌H++X−initialcAtequilibriumc−c\alphac\alphacαHX\overset{}{⇌}{H}^{+} + {X}^{-}initialcAtequilibriumc - c \alphac \alphac \alpha

The acid dissociation constant, Ka=cα21−α{K}_{a} = \dfrac{{c \alpha}^{2}}{1 - \alpha}

⇒Ka=c(Λm/Λmo)21−(Λm/Λmo)⇒ {K}_{a} = \dfrac{c{\left({Λ}_{m} / {Λ}_{m}^{o}\right)}^{2}}{1 - \left({Λ}_{m} / {Λ}_{m}^{o}\right)}

⇒Ka=cΛm2Λmo(Λmo−Λm)⇒ {K}_{a} = {cΛ}_{m}^{2}{Λ}_{m}^{o}\left({Λ}_{m}^{o} - {Λ}_{m}\right)

KaΛmo2−KaΛmoΛm=cΛm2{K}_{a}{Λ}_{m}^{o}2 - {K}_{a}{Λ}_{m}^{o}{Λ}_{m} = {cΛ}_{m}^{2}

KaΛmo2Λm−KaΛmo=CΛm\dfrac{{K}_{a}{Λ}_{m}^{o}2}{{Λ}_{m}} - {K}_{a}{Λ}_{m}^{o} = {CΛ}_{m}

KaΛmo2Λm=cΛm+KaΛmo\dfrac{{K}_{a}{Λ}_{m}^{o}2}{{Λ}_{m}} = {cΛ}_{m} + {K}_{a}{Λ}_{m}^{o}

1Λm=(cΛmKaΛmo2)+1Λmo\dfrac{1}{{Λ}_{m}} = \left(\dfrac{{cΛ}_{m}}{{K}_{a}{Λ}_{m}^{o}2}\right) + 1{Λ}_{m}^{o}

From the above line equation, slope and y-intercept can be written as follows,

P=1ΛmoP = 1{Λ}_{m}^{o}

S=1KaΛmo2S = \dfrac{1}{{K}_{a}{Λ}_{m}^{o}2}

PS=(1Λmo1KaΛmo2)=KaΛmo\dfrac{P}{S} = \left(\dfrac{1{Λ}_{m}^{o}}{\dfrac{1}{{K}_{a}{Λ}_{m}^{o}2}}\right) = {K}_{a}{Λ}_{m}^{o}

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