Acidity and Alkalinity of Water

The acidity of water sample is its capacity to neutralise a base whereas its alkalinity is a measure of its capacity to neutralise acids. Natural waters may be acidic or a i ka 1 ine, depending upon the source of water and the extent and nature of pollutants iiof. industry and municipal sanitary disposal. 

Most natural waters contain dissolved CO2. It may enter water by absorption from atmo there or may be produced by biological oxidation of organic matter vi/ith which has been in contact, e.g.. 

CO2 content of surface waters is normally much less than 10 mg/1 but some ground waters may contain between 30 to 50 mg/1 of CO2. When waters containing high concentration of CO2 are exposed to atmoi.phere, most of CO2 escapes from the solutions as the partial pressure of CO2 in atmosphere is normally much less. 

Waters may be acidic due to the presence of CO2 and/or organic acids Conned by the decay of organic matter, e.g., 

Hexose bacteria propanoic acid acetic acid formic acid 

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The acidity and alkalinity of water solutions and, therefore, differences in their acidity or alkalinity, can be quantified and assigned numerical values. One way of doing this is to express the concentration of hydrogen ions in solutions on a numerical scale. Such a scale is provided by the widely accepted pH scale, in which the strength or weakness of acid or alkaline... 

The reduced mobility of radium in comparison with uranium is explained by the solubility difference between the two elements, which occur in nature as sulphates and carbonates at 18°C radium sulphate = 1.410" g/1 uranyl sulphate = 205 g/1 radium carbonate is insoluble and uranyl carbonate = 60g/l. With the acidity and alkalinity of water, however, radium solubility changes. The radium content of water also depends on the salt concentration of certain elements—mainly alkaline chloride (radium replaces sodium). Radium precipitates with complexes of barium (S04Ba) and with calcium carbonates (travertine). Radium is also fixed by clay, organic matter, iron and manganese hydroxides. 

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