To calculate the pH of a 0.1 M solution of hydrochloric acid HCl , we need to determine the concentration of hydrogen ions H+ in the solution. HCl is a strong acid, which means it dissociates completely in water, producing H+ and Cl- ions.Step 1: Write the dissociation equation for HCl:HCl H+ + Cl-Step 2: Determine the concentration of H+ ions:Since HCl dissociates completely, the concentration of H+ ions will be equal to the concentration of HCl. In this case, the concentration of H+ ions is 0.1 M.Step 3: Calculate the pH using the pH formula:pH = -log[H+]Plug in the concentration of H+ ions:pH = -log 0.1 Step 4: Solve for pH:pH = 1The pH of a 0.1 M solution of hydrochloric acid is 1 when measured using a pH meter.