Water Analysis - Hypothetical Combinations - Page 3

The hardness as CaC03 of the mineral compounds in water can be determined if the chemical analysis of the water is known. The concentrations of each of the hardness-forming impurities are divided by the equivalent weight of the compound and multiplied by the equivalent weight of CaC03. Here are a few of these equivalent weights:

To determine the equivalent weight of any mineral compound in terms of calcium carbonate:

equals the concentration of that mineral as CaC03

For example:

10.0 gpg MgSO4 X equivalent wt CaCO₃, / equivalent wt MgSO₄, concentration of MgSO₄, as CaCO₃,

10.0 X 50.045 / 60.187 = 8.3 gpg as CaCO₃

Traces of elements or compounds are not normally considered in these calculations. Iron, for example, would not be included, unless present in extremely high concentrations.

In the example shown above, the calcium and bicarbonates are combined first. The excess bicarbonates are then combined with the magnesium. The analysis still does not balance, and the remaining magnesium is combined with part of the sulfates present. The remaining sulfates and all of the chlorides are expressed as sodium compounds. (Adding 5.0 gpg Ca ++ as CaCO3, to 5.0 gpg HC03- as CaCO3, produces 5.0 gpg Ca(HC03)2 as CaC03, not 10 gpg.)

Table of Equivalent Weights