Diluting Acids and Bases – How Does the pH Change?

ChemistryAcids, Bases & TitrationAges 16–17

A virtual experiment with a pH meter: start from an HCl, CH₃COOH, NaOH or NH₃ solution of concentration C; at each dilution step keep one portion and add distilled water up to the mark (10-fold or 100-fold). The table of pH after each step and the graph of pH against log(dilution factor) show that a strong acid rises by 1 pH unit for every 10-fold dilution, a weak acid by only about 0.5, and that the pH never crosses 7 because water itself ionizes.