Hardness

Authored by: Pradyot Patnaik

Handbook of Environmental Analysis

Print publication date:  August  2017
Online publication date:  August  2017

Print ISBN: 9781498745611
eBook ISBN: 9781315151946
Adobe ISBN:

10.1201/9781315151946-33

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Abstract

Hardness of a water sample is a measure of its capacity to precipitate soap. The presence of calcium and magnesium ions in water essentially contributes to its hardness. Other polyvalent ions, such as aluminum, also cause hardness. Their effect, however, is minimal, because these polyvalent ions occur in water often in complex forms and not as free ions. As a result, they cannot precipitate soap. Although calcium is not the only cation causing hardness, for the sake of convenience, hardness is expressed as mg CaCO3/L. Similarly, anions other than carbonate, such as bicarbonate, also cause hardness in water. To distinguish the contributions of such anions from carbonates, hardness is sometimes termed as “carbonate hardness” and “noncarbonate hardness.” This can be determined from alkalinity. The relationship is as follows.

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