Final answer:
The equilibrium concentration of S²⁻ in a 0.20 M H₂S solution is related to the acid dissociation constants, but the specific value cannot be calculated without additional details on equilibrium expressions and calculations.
Step-by-step explanation:
The student is asking about the equilibrium concentration of S²⁻ ions in a 0.20 M H₂S solution. Given the acid dissociation constants (Ka1 and Ka2), the concentration of hydrosulfide ions (HS⁻) produced from the first dissociation is relatively higher than that of the sulfide ions (S²⁻) from the second dissociation due to the significant difference in the magnitude of the two constants (Ka1 = 1x10⁻⁷ and Ka2 = 1x10⁻⁹).
Therefore, the concentration of H⁺⁺S remains nearly constant, and the contribution of HS⁻ dissociation to the hydrogen ion concentration can be deemed negligible.
In calculating the S²⁻ concentration, we use the overall equilibrium constant, K, which is the product of its stepwise constants Ka1 and Ka2. We can then relate this to the given concentration of H₂S to find the necessary hydrogen ion concentration to achieve a certain sulfide ion concentration.
However, without additional details like the equilibrium expressions and calculations, we cannot provide a specific numerical answer to the student's question. Future calculations would involve setting up the expressions for the dissociation equilibria and performing calculations to solve for [S²⁻].