Final answer:
The Ka of the acid is approximately 0.021.
Step-by-step explanation:
The dissociation of a weak acid can be represented by the equation:
HA ⇌ H⁺ + A⁻
In this case, the weak acid is 12.5% dissociated, which means that the concentration of the weak acid is 12.5% of the initial concentration. Let's assume the initial concentration of the weak acid is x M. So, the concentration of the weak acid is 0.125x M, and the concentration of the dissociated ions (H⁺ and A⁻) is also 0.125x M.
The ionization constant, Ka, can be calculated using the following equation:
Ka = [H⁺][A⁻] / [HA]
Substituting the values we obtained from the dissociation:
Ka = (0.125x)(0.125x) / (0.737x)
Simplifying the equation:
Ka = 0.015625x² / 0.737x
Cancelling out x:
Ka = 0.015625 / 0.737
Ka ≈ 0.021
Therefore, the ka of the acid is approximately 0.021.