Galvanic cells in which the electrode potential of one of the electrodes depends on hydrogen ion concentration, [H⁺], form the basis of pH measurements. Commercial pH meters make use of a glass electrode and a reference electrode like the saturated calomel electrode (SCE) to measure pH. Acid-base and redox titrations can be carried out more accurately using potentiometry than by using indicators. Determination of solubility products, pK_a and pK_b has also been described in this lecture. The elcetrochemical basis for the design of sensors has been given. The determination of thermodynamic functions and activities using emf has been illustrated in this and the earlier two lectures.