MHT CET202523 Apr 2025Morning ShiftChemistryIonic EquilibriumActual
A weak base is 5 % dissociated in its 0.01 M solution. Calculate the dissociation constant.
Options
- A3.5 10⁻⁶
- B2.0 10⁻⁵
- C2.3 10⁻⁴
- D2.5 10⁻⁵
Correct answer
D. 2.5 10⁻⁵
Step-by-step solution
The weak base with initial concentration C = 0.01 , M has percentage dissociation 5 % , so the degree of dissociation is = 0.05 . For the equilibrium B + H₂O BH^+ + OH^- , the base dissociation constant is expressed as K_b = [BH^+][OH^-] [B] . At equilibrium, [B] = C(1 - ) , [BH^+] = C , and [OH^-] = C . Substituting these into K_b gives K_b = C ^2 1 - . Since = 0.05 is small, 1 - 1 , and K_b C ^2 = 0.01 (0.05)^2 = 2.5 10⁻⁵ . This matches option D , so the answer is D .