Final answer:
To find the initial concentration of thiosulfate ion in the reaction, we use the given concentration of the Ag(S₂O3)2³- complex (0.00532 M) and the stoichiometry of the dissolution equilibrium. We then apply the equilibrium constant expression to solve for the concentration of thiosulfate ion.
Step-by-step explanation:
The student is asking about the initial concentration of thiosulfate ion in a reaction. To answer this, we utilize the given equilibrium concentration of the complex, [Ag(S₂O3)2³-] = 0.00532 M, and the known stoichiometry of the dissolution, where the concentration of aqueous silver ion is the same at 0.00532 M. The large equilibrium constant (Kf) for the formation of the complex indicates that nearly all silver ions will be complexed with the thiosulfate ions.
The equation [Ag(S₂O3)2³-][Br] = (0.00532 M)(0.00532 M) / [S₂O3²-] is used, where the equilibrium constant K is provided. Solving for [S₂O3²-], we can determine the initial concentration of thiosulfate. Additionally, from the stoichiometry of the reaction involving Na2S₂O3, the mass of Na2S₂O3 needed can be calculated based on Ag(S₂O3)2³- concentration.