ABSTRACT

Hardness of a water sample is a measure of its capacity to precipitate soap. e presence of calcium and magnesium ions in water essentially contributes to its hardness. Other polyvalent ions, such as aluminum, also cause hardness. eir e ect, however, is minimal, because these polyvalent ions occur in water o en 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.” is can be determined from alkalinity. e relationship is as follows:

When the total hardness measured in the sample is numerically greater than the sum of both carbonate alkalinity and bicarbonate alkalinity, then

Carbonate hardness carbonate alkalinity bicarbonate alkalinity= +

and

Noncarbonate hardness total hardness-carbonate hardness=

or

Total hardness-(carbonate alkalinity bicarbonate alkalinity)+

When total hardness is equal to or less than the sum of carbonate and bicarbonate alkalinity, all hardness is noncarbonate hardness only and there is no carbonate hardness.