How this calculation works
Hardness expressed as calcium carbonate is an equivalent reporting convention, not proof that all dissolved material is calcium carbonate. A standardized EDTA titre measures an amount that is converted into that common mass basis. This calculation includes a separate blank and original-sample dilution factor. It is intended for checking entered laboratory arithmetic after a suitable titration has already been performed.
Hardness mg/L as CaCO₃ = M_EDTA (titre−blank) ×100.0869 ×1000/sample_mL ×dilutionA worked example
At 0.01 molar EDTA, a ten-millilitre corrected titre represents 0.1 millimole of divalent ions. In a fifty-millilitre aliquot, the resulting equivalent concentration is 200.1738 milligrams per litre as calcium carbonate. If the aliquot represents an original sample diluted twofold, the original-sample result doubles. If observed titre becomes eleven millilitres with a one-millilitre blank, the corrected amount remains unchanged.
Good to know
Endpoint selection, buffering conditions and interfering metals are not evaluated. The model does not decide whether the titration was selective, complete or performed under a validated method. The result is not a drinking-water safety verdict or a diagnosis. Retain the actual laboratory method, standardized titrant details and quality-control records when interpreting a measured sample.
Reference: NEMI — EPA 130.2 EDTA total hardness method (opens in a new tab) ↗
What this calculation answers
Hardness expressed as calcium carbonate is an equivalent reporting convention, not proof that all dissolved material is calcium carbonate. A standardized EDTA titre measures an amount that is converted into that common mass basis.
This calculation includes a separate blank and original-sample dilution factor. It is intended for checking entered laboratory arithmetic after a suitable titration has already been performed.
The Molarity calculator supplies a concentration-unit check. A hardness equivalent additionally needs the corrected titre, aliquot volume and original-sample dilution.
Use the right input conventions
EDTA concentration is molarity, not a mass concentration or an assumed titrant factor. Enter both observed and blank titres in millilitres, with the blank no greater than the observed volume.
Sample volume is the actual diluted aliquot titrated. The dilution multiplier restores its calculated concentration to the original sample, so a tenfold dilution uses ten rather than adding an extra volume correction elsewhere.
Interpret the result
The divalent-ion amount follows one-to-one EDTA stoichiometry. Multiplying by the molar mass of calcium carbonate produces the equivalent mass used in the hardness result, regardless of how the calcium and magnesium shares are distributed.
Corrected titre is shown separately to make blank subtraction inspectable. A zero corrected titre produces zero reported equivalent under the model, without making a claim about an analytical detection limit.
Work through the example
At 0.01 molar EDTA, a ten-millilitre corrected titre represents 0.1 millimole of divalent ions. In a fifty-millilitre aliquot, the resulting equivalent concentration is 200.1738 milligrams per litre as calcium carbonate.
If the aliquot represents an original sample diluted twofold, the original-sample result doubles. If observed titre becomes eleven millilitres with a one-millilitre blank, the corrected amount remains unchanged.
Where the model stops
Endpoint selection, buffering conditions and interfering metals are not evaluated. The model does not decide whether the titration was selective, complete or performed under a validated method.
The result is not a drinking-water safety verdict or a diagnosis. Retain the actual laboratory method, standardized titrant details and quality-control records when interpreting a measured sample.
A few questions, answered
Does hardness as CaCO3 identify the dissolved compound?
No. It is a common equivalent-mass reporting basis for the entered titration amount.
What changes in the comparison?
Blank correction keeps the titrated amount unchanged, while the twofold original-sample dilution doubles its reported concentration.