Potentiometry is a technique used to measure the potential voltage of an electrochemical cell to determine the concentration of a specific ion in a solution. In this case, we want to determine the concentration of chloride ions Cl- in a 0.10 M solution of hydrochloric acid HCl .However, in this particular case, potentiometry is not necessary to determine the concentration of chloride ions. This is because hydrochloric acid is a strong acid that completely dissociates in water, meaning that for every one mole of HCl, one mole of H+ and one mole of Cl- are produced.So, in a 0.10 M solution of HCl, the concentration of chloride ions Cl- will also be 0.10 M.