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Water Analysis - Hypothetical Combinations


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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:


Hardness Producing Compound Equivalent Weight
Magnesium sulfate MgS04 60.187
Calcium bicarbonate Ca(HC03)2 81.057
Calcium chloride CaCl2 55.493

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

concentration of the mineral X equivalent weight of CaCO3
equivalent weight of mineral

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

Aluminum 8.994 Hydroxide 17.007
Ammonium 18.0386 Carbonate 30.005
Calcium 20.040 Bicarbonate 61.017
Hydrogen 1.00797 Sulfate 48.031
Iron (ferrous) 27.924 Chloride 35.453
Iron (ferric) 18.614 Nitrate 62.005
Magnesium 12.156 Phosphate 31.657
Potassium 39.102 Fluoride 18.998
Sodium 22.9898 Sulfide 16.032


Aluminum sulfate 57.025 Magnesium bicarbonate 73.173
Calcium carbonate 50.045 Magnesium chloride 47.609
Calcium bicarbonate 81.057 Magnesium sulfate 60.187
Calcium sulfate 68.071 Sodium bicarbonate 84.007
Calcium chloride 55.493 Sodium carbonate 52.995
Calcium hydroxide 37.047 Sodium sulfate 71.021
Magnesium carbonate 42.161    


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Related Articles:

How to Interpret Water Analyses
Water Analysis Example NO. 2
Water Analysis Example NO. 3


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