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Determination of Temporary Hardness

Estimation of  Water Hardness

The estimation of water hardness as applied to boiler water and other water is great interest for the chemical industry in general.the determination of water hardness has always been an especially important factor in the manufacturing control of sugar industry, pharmaceuticals, food processing, leather, gums, adhesives, textiles etc.

Determination of Hardness  by  O. Hehner’s Methods

Temporary hardness is determined by finding the alkalinity of water before boiling and that left after boiling. This is because temporary hardness is removed on boiling.
Ca(HCO3)2    ——–>   CaCO3 + H2O + CO2
Mg(HCO3)2    ——–>   Mg(OH)2 + 2CO2

Pipette out 50 ml of water sample in a conical flask. Add 2-3 drop of methyl orange indicator. Titrate againist N/50 HCl. Note the volume of acid used (asign V1 ml). Now take 100ml of water sample in a pyrex beaker and evaporate it to dryness. Add about 50 ml of distilled water, warm, stirr to dissolve the soluble portionleft. Filter the solution and wash the residue with distilled water. Make up the voulume to 100 ml in a measuring flask, by adding distilled water. Take 50 ml of this filtrate in a conical flask and titrate againist N/50 HCl using methyl orange as indicator. Left the volume of acid used be V2 ml.

Volume of N/50 HCl used by temporary hardness present in 50 ml of water = (V1-V2)ml
Alkalinity due to Temporary Hardness in 50 ml of water sample                  = (V1-V2)ml of N/50HCl
Strength of alkalinity due to temporary hardness in terms of CaCO3 equivalents
                                                                                                                                                              = (V1-V2) X 1 X 50 / 50 X 50
                                                                                                                                                              = (V1-V2)/50g of CaCO3 eqt/litre
                                                                                                                                                              = (V1-V2) X 100000/50 X 1000 ppm

    Therfore Temporary Hardness = 20(V1-V2)ppm

3 Responses to “Determination of Temporary Hardness”

  1. nor says:

    can some share on the application of phosphorus acid method for decomplexing agent to WWTP

  2. Shashikumar says:


  3. Kamlesh kumar says:

    Colour change should be mentioned at the end point.

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