Q56 / 180 · NEET 2025 · Chemistry

If the molar conductivity $\left(\Lambda_{\mathrm{m}}\right)$ of a $0.050 \mathrm{~mol} \mathrm{~L}^{-1}$ solution of a monobasic weak acid is $90 \mathrm{~S} \mathrm{~cm}^2 \mathrm{~mol}^{-1}$, its extent (degree) of dissociation will be [Assume $\Lambda_{+}^{\circ}=349.6 \mathrm{~S} \mathrm{~cm}^2 \mathrm{~mol}^{-1}$ and $\left.\Lambda_{-}^{\circ}=50.4 \mathrm{~S} \mathrm{~cm}^2 \mathrm{~mol}^{-1}.\right]$

  • A
    0.115
  • B
    0.125
  • Correct answer
    C
    0.225
  • D
    0.215

Solution

$\begin{aligned} &\text { Degree of dissociation }(\alpha)=\frac{\wedge_m}{\wedge_m^{\circ}}\\ &\begin{aligned} \wedge_{\mathrm{m}}^{\circ} & =\wedge_{+}^{\circ}+\wedge_{-}^{\circ} \\ & =349.6+50.4=400 \mathrm{Scm}^2 \mathrm{~mol}^{-1} \\ \therefore \alpha & =\frac{\Lambda_{\mathrm{m}}}{\Lambda_{\mathrm{m}}^{\circ}}=\frac{90}{400}=0.225 \end{aligned} \end{aligned}$

Hence, the correct answer is option: 'C'.

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