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1.908 g of N-2-acetamido-2-aminoethane-sulfonic acid potassium salt (ACES-K , MW = 220.29 g/mol) is dissolved in 54.44 mL of water. 26.37 mL of HCl is added to the solution, resulting in a pH of 6.84. Calculate the concentration of the HCl solution. The pKa of ACES is 6.85.