Q. The equivalent conductance of M/32 solution of a weak monobasic acid is 8.0 mhos cm² and at infinite dilution is 400 mhos cm². The dissociation constant of this acid is:
A) 1.25 × 10⁻⁶
B) 6.25 × 10⁻⁴
C) 1.25 × 10⁻⁴
D) 1.25 × 10⁻⁵
Explanation
[Solution from source] Degree of dissociation α = 8.0/400 = 0.02. Ka = Cα²/(1 − α) ≈ Cα² = (1/32)(0.02)² = 1.25 × 10⁻⁵. Forgetting to square α gives 6.25 × 10⁻⁴. Answer (4).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.