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Chemistry · PYQ NEET UG 2021
हिन्दीThe molar conductivity of \( 0.007\text{ M} \) acetic acid is \( 20\text{ S cm}^2\text{ mol}^{-1} \). What is the dissociation constant of acetic acid? Choose the CORRECT option. [Given: \( \Lambda_{\text{H}^+}^\circ = 350\text{ S cm}^2\text{ mol}^{-1} \), \( \Lambda_{\text{CH}_3\text{COO}^-}^\circ = 50\text{ S cm}^2\text{ mol}^{-1} \)]
Correct answer · Option 2
\( 1.75 \times 10^{-5}\text{ mol L}^{-1} \)
Explanation
\( \Lambda_m^\circ = 350 + 50 = 400 \). Degree of dissociation \( \alpha = \frac{\Lambda_m}{\Lambda_m^\circ} = \frac{20}{400} = 0.05 \). Dissociation constant \( K_a = \frac{c\alpha^2}{1-\alpha} \approx c\alpha^2 = 0.007 \times (0.05)^2 = 1.75 \times 10^{-5}\text{ mol L}^{-1} \).
