Calculate Groundwater Hardness as CaCO3
Groundwater hardness is commonly expressed in terms of the equivalent concentration of calcium carbonate (CaCO3). To calculate hardness from the concentration of specific ions like Ca++, a conversion factor based on their equivalent weights is used.
Determine Conversion Factor
The conversion factor is the ratio of the equivalent weight (EW) of CaCO3 to the EW of the ion (Ca++ in this case).
- Equivalent Weight (EW) = Molecular Weight (MW) / Valence (n)
- EW of CaCO3 = (100.09 g/mol) / 2 = 50.05 g/eq
- EW of Ca++ = (40.08 g/mol) / 2 = 20.04 g/eq
- Conversion Factor =
$ \frac{EW_{CaCO_3}}{EW_{Ca^{++}}} $ - Conversion Factor =
$ \frac{50.05 \text{ g/eq}}{20.04 \text{ g/eq}} \approx 2.5 $
Calculate Total Hardness
Multiply the concentration of the ion by the conversion factor to get the hardness expressed as CaCO3.
- Hardness (as CaCO3) = [Ca++] (in mg/l) × Conversion Factor
- Hardness (as CaCO3) = 100 mg/l × 2.5
- Hardness (as CaCO3) = 250 mg/l
Therefore, the hardness of the groundwater sample is 250 mg/l as CaCO3.
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