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

=127.36 mg /L Ca as CaCO3

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Author: T.P.Sivanandan

11 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

  4. Calculation above is wrong.

    If x=51 x 50.045/20.04,
    then x=127.36 mg /L Ca as CaCO3
    not x= 124.8!

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