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:
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
CATIONS | ANIONS | ||
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 |
COMPOUNDS | |||
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 |