Calculating Calcium Hardness as CaCO3

Calculating Calcium Hardness as CaCO3

The hardness (in mg/L as CaCO3) for any given metallic ion is calculated using Equation

Calcium hardness (m/L) as CaCO3/equivalent weight of CaCO3

= Calcium (mg/L)/equivalent weight of calcium


A water sample has calcium content of 51 mg/L. What is this calcium hardness expressed as CaCO3?

Referring to Equation:

x mg/L /50.045=51 mg/L /20.04

x=51 x 50.045/20.04

=124.8 mg /L Ca as CaCO3

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Author: T.P.Sivanandan

9 thoughts on “Calculating Calcium Hardness as CaCO3”

  1. Frank R. Spellman and it states that the answer is 124.8 mg/L Ca as CaCO3.

    Seems to follow the calculation I always knew of 2.5(Ca++) thus 2.5*51=127.5 mg/L
    Close enough…….

    Who’s right and who’s wrong?

  2. Molar mass (CO3(2-)) = M(C) + 3 x M(O) = 12+ 3 x 16 = 60 g/mole. Molar mass (CaCO3) = M(Ca) + M(C) + 3 x M(O) = 40 + 12 + 3 x 16 = 100 g/mole. Divide the molar mass by the ion charge or oxidation number (for CaCO3) to determine equivalent (Eq.) weights. Eq. weight (HCO3(-)) = 61 / 1 (charge) = 61 g/Eq.

    So eq wt of Caco3 is 61g/eq it is ok

  3. Pls can u apply this conversion to to any sample of interest esp soil sample. Hw many unit do you av to subtract to obtain an accurate accuracy figure?.. reply ASAP pls

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