10.0 mL of a Cu2+ solution of unknown concentration was placed in a 250 mL Erlenmeyer flask. An excess of KI solution was added. Indicator was added and the solution was diluted with H2O to a total volume of 75 mL. The solution was titrated with 0.25 M Na2S2O3. The equivalence point of the titration was reached when 11.65 mL of Na2S2O3 had been added. What is the molar concentration of Cu2+ in the unknown solution?
Assistance:
2Cu2+ + 4KI → 2CuI + I2 + 4K+ (rxn 1)
I2 + 2Na2S2O3 → 2NaI + Na2S4O6 (rxn 2)