Acidity and Alkalinity - Chemical Characteristics of Water

Acidity:

Capacity to neutralize bases and is a measure of acids in water. Acidity is measured by titrating the sample using a standard base solution to raise to a pH of 8.3

Alkalinity:

Ability of water to neutralize acids, caused mainly by bicarbonate, carbonate and hydroxyl ions.  

Alkalinity (eq/m³)  = HCO₃^-, bicarbonate (eq/ m³) + CO3^-2, carbonate (eq/ m³)  + OH^-, hydroxyl (eq/ m³) - H⁺, hydrogen (eq/ m³)  

For all practical purposes the last two terms can be ignored for natural water samples. Even carbonate concentrations are very low in the natural pH range thus leaving mainly bicarbonate as the cause of alkalinity.   

Convert alkalinity from eq/m³ into mg/l as CaCO₃ by multiplying with 50 (EW of CaCO₃)

Alkalinity is measured by titrating the sample with a standard acid to a pH of 4.5.