Let's work through the problem step by step.
The dissociation of the weak acid is given by:
HA⇌H++A−.The initial concentration of HA is 0.5 M . With a degree of dissociation,
α=0.01 (or 1\%), the equilibrium concentrations are:
[HA]=0.5(1−0.01)=0.5×0.99=0.495M[H+]=0.5×0.01=0.005M[A−]=0.005MThe acid dissociation constant,
Ka, is defined as:
Ka=.Substitute the equilibrium concentrations:
Ka==.Simplifying the expression:
Ka≈5×10−5.Thus, the approximate value of
Ka (or
Ke, as referenced) is
5×10−5.
The correct option is Option B.
