Q. The molar conductivity of 0.007 M acetic acid is 20 S $cm^2$ $mol^{-1}$. What is the dissociation constant of acetic acid? Choose the correct option. [$\Lambda^\circ_{H^+} = 350$ S $cm^2mol^{-1}$, $\Lambda^\circ_{CH_3COO^-} = 50$ S $cm^2mol^{-1}$]
A) $2.50 \times 10^{-4}$ mol $L^{-1}$
B) $1.75 \times 10^{-5}$ mol $L^{-1}$
C) $2.50 \times 10^{-5}$ mol $L^{-1}$
D) $1.75 \times 10^{-4}$ mol $L^{-1}$
Explanation
[Solution] $\Lambda^\circ = 400$, $\alpha = 20/400 = 0.05$; $K_a \approx c\alpha^2 = 0.007 \times 0.0025 = 1.75 \times 10^{-5}$ mol $L^{-1}$. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.