How Do You Measure Hardness Of Water Samples?


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Sadia Batool Profile
Sadia Batool answered
Hardness is measured by complexomtric titration.
1- Ammonia Buffer Solution: Dissolve 16.9 g ammonium chloride in concentrated ammonium hydroxide. Add 1.25 g of magnesium salt of EDTA and dilute to 250 ml with distilled water.
2- Erichrome Black Tea: (Sodium salt of 1-(- hydroxy-2-naphthylazo)-5- nitro-2- naphthol-4-sulphonic acid): Dissolve 0.5 g dye in 100 ml ethylene glycol mono methyl ether or ethyl alcohol.

3- Standard EDTA titrant (0.01M or 0.02N): 3.723 g analytical reagent grad disodium salt of ethylene diamminetetraacetate (EDTA) is dissolved in distilled water and dilute to 1000 ml and is standardized against standard Calcium solution.
4- Standard Calcium Solution: weigh 1g anhydrous CaCO3 (primary standard) into the 500 ml flask and HCL were add until all CaCO3 has dissolved. Added 200ml distill water and boil for few minutes to expel CO2. Cool it, add a few drops of methyl red indicator and adjust the pH with NH4OH to above pH –8 (Fzanson A, M. 1985).

50 ml of sample was titrate with standard EDTA solution.
Hardness mg/L= A´N ´ 50,000 / ml of sample
A= ml of EDTA used
N = Normality of EDTA
All the readings are to be calculated and compiled in tabular form. Then there mean is found. We analyze this parameter both for drinking water and sewage.

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