1. Principles
Measurement of pH is one of the most important and frequently used tests in water chemistry. Practically every phase of water supply and wastewater treatment (e.g., acid–base neutralization, water softening, precipitation, coagulation, disinfection, and corrosion control) is pH-dependent. A pH is used in alkalinity and carbon dioxide measurements and many other acid–base equilibria. At a given temperature the intensity of the acidic or basic character of a solution is indicated by pH or hydrogen ion activity. Acidity and alkalinity are the acid- and base-neutralizing capacities of a water and usually are expressed as milligrams per liter of CaCO3. Buffer capacity is the amount of strong acid or base, usually expressed in moles per liter, needed to change the pH value of a 1-L sample by 1 unit. The basicity or acidity of a solution is estimated by pH, a scale that is defined as the –log[H+]. Pure water is very slightly ionized and at equilibrium the ion product is