Final answer:
The pH at the equivalence point for the first dissociation of carbonic acid will be slightly basic since the bicarbonate ion acts as a weak base. Among the given options, d. pH = 8.00 is the closest to the expected pH at the equivalence point. The actual pH would be calculated based on the bicarbonate concentration.
Step-by-step explanation:
The question refers to the pH at the equivalence point during the first dissociation of carbonic acid, H₂CO₃. Considering the given equilibrium concentrations, we can use the concentration of the hydronium ions (H₃O⁺) to calculate the pH. The key formula we'll be using is pH = -log[H₃O⁺].
Using the given concentration of hydronium ions [H₃O⁺] = 1.2 × 10⁻⁴ M, the pH is calculated as follows:
pH = -log(1.2 × 10⁻⁴) ≈ 3.92
However, this calculated pH does not apply to the equivalence point scenario. To correctly determine the pH at the equivalence point, we must consider the products of the dissociation at that point, which will predominantly be the conjugate base HCO₃⁻ (bicarbonate) reacting with water to produce H₃O⁺ and CO₃²⁻ (carbonate). Since bicarbonate is the conjugate base of a weak acid, it will have basic properties, and thus the pH at the equivalence point will be greater than 7. In the various examples provided, we can observe scenarios where bicarbonate ions contribute to a pH higher than 7, indicating the basic nature of the solution at the equivalence point.
Therefore, in the given options, the closest correct answer would be d. pH = 8.00, reflecting that the solution is slightly basic at the equivalence point due to the presence of the bicarbonate ions acting as a base.