In a 0.1 M solution of hydrochloric acid HCl , the concentration of chloride ions Cl- is equal to the concentration of HCl because HCl dissociates completely into H+ and Cl- ions in aqueous solution. Therefore, the concentration of chloride ions in the solution is 0.1 M.The potential difference between the two silver electrodes in contact with the solution is measured to be 0.22 V, which is equal to the standard reduction potential for the silver/silver chloride electrode. Since the measured potential difference is equal to the standard reduction potential, this indicates that the solution is at equilibrium with respect to the silver/silver chloride electrode reaction.At equilibrium, the concentration of chloride ions in the solution remains constant, so the concentration of chloride ions in the 0.1 M solution of hydrochloric acid is 0.1 M.