A 1,695.5 mL aqueous solution of 705.3 mM Na₂S is combined with 100.0 mL of an aqueous HCl solution whose HCl concentration is not known. The reaction produces 1.983 L of H₂S gas at a pressure of 1.00 atm and a temperature of 30.76C. There is some Na₂S remaining after the reaction is complete. What is the concentration of sulfide ions in the solution after the reaction has completed? Assume the volumes of the solutions are additive. Express your answer in units of millimolar (mM) using at least three significant digits.