MHT CET202525 Apr 2025Evening ShiftChemistryIonic EquilibriumActual
A monobasic weak acid dissociates 2 % in its 0.002 M solution. Calculate the dissociation constant of weak acid.
Options
- A2 10⁻⁹
- B8 10⁻⁷
- C6 10⁻⁷
- D4 10⁻⁶
Correct answer
B. 8 10⁻⁷
Step-by-step solution
Dissociation constant calculation for weak acids For a weak acid HA with dissociation equilibrium HA H ^+ + A ^- , the acid dissociation constant is given by K_a = [ H ^+][ A ^-] [ HA ] . Given initial concentration C = 0.002 M and percentage dissociation 2%, the degree of dissociation is = 0.02 . From the equilibrium concentrations [ H ^+] = [ A ^-] = C and [ HA ] = C(1- ) , the dissociation constant becomes K_a = C ^2 1- . Since = 0.02 is sufficiently small, we apply the approximation 1- 1 , yielding K_a C ^2 . S