Answer:
Ka = 6.02x10⁻⁶
Step-by-step explanation:
The equilibrium that takes place is:
We calculate [H⁺] from the pH:
- [H⁺] =

Keep in mind that [H⁺]=[A⁻].
As for [HA], we know the acid is 0.66% dissociated, in other words:
We calculate [HA]:
Finally we calculate the Ka:
- Ka =
= 6.02x10⁻⁶