Thursday, August 27, 2020

Hardness of Water

Determination the Hardness of Water

 Hardness of Water

Hardness of water image

Hardness of water is one of the most important phenomenon and the Hardness of water can be tested according to the guideline of BIS. The Hardness of water need to find out for the aspect of drinking purpose or household purpose. Therefore The Hardness of water test is important in Civil engineering studies.

Hardness is a phenomenon of water to cause precipitation of insoluble calcium and magnesium salts of higher fatty acids from soap solutions. Hardness may be discussed into two types– permanent hardness & temporary hardness. Temporary hardness may be categorized  due to the presence of bicarbonates of calcium and magnesium. whereas The Permanent hardness is non-carbonate hardness and is categorized due to the presence of sulphates, chlorides and nitrates of calcium and magnesium.

Hardness of water is significant parameter in determining the suitability of water for domestic and industrial uses as per BIS Standard. The comparative amount of calcium and magnesium hardness, carbonates and non-carbonates hardness present in water are the fundamental process while determining the most economical type of softening process.

Complexometric Titration is a generic term involving the titration which are based on the formation of a soluble complex between a metal ion and a complexing agent.The metal ion is known as central atom and the complexing agent is known as ligand.

The hardness of water may be determined as standard method by complexometric titration. EDTA can be used as complexing agent.The Ca2+ and Mg2+ present in water are titrated with EDTA using Eriochrome Black-T as indicator.

EDTA image

i)                First,the indicator EBT, which is blue coloured, forms an unstable complex with calcium and magnesium ions in water at a PH of 9 to 10.The complex is wine red in colour.

[Ca2+/Mg2+ + EBT ®Ca/Mg-EBT] {Unstable complex(wine-red)}

ii)              As the solution is titrated against, the free Ca2+ and Mg2+ ions in water form stable metal ion EDTA complex.

[Ca2+/Mg2+ + EDTA®Ca/Mg-EDTA] {stable complex(colorless)}

   Once the free metal ions are complexed ,the EDTA replaces Calcium and Magnesium ions from the unstable indicator complex,to form a stable complex with the result ,the indicator is blue in colour at the above mentioned PH,the end point is the appearance of blue colour.

[Ca/Mg-EBT]+EDTA®[Ca/Mg-EDTA]+EBT ( blue)


  • Conical flask 
  • Burette
  • Measuring cylinder 
  • Beaker
  • Dropper
  • Volumetric flask


  •  0.01(N) EDTA solution 
  • EBT indicator
  • Buffer solution
  • Water sample


For water sample:

  1. Rinse and fill the burette with EDTA solution.
  2. Pipette out 25 m.l water sample and add 2-3 m.l (NH4OH+NH4Cl) buffer solution.
  3. Add 2-3 drops of EBT indicator and colour of the solution is wine-red.
  4. Titrate against 0.01(M) EDTA solution till the colour of the solution changes from wine-red to blue.

Hardness test table image


For water sample:
1000 m.l 1(M) EDTA  =   100 g of CaCO3
1 m.l 0.01 (M) EDTA =  100 X 1/1000 X 1/100 g of CaCO3 = 1 mg of CaCO3
V    m.l  0.01 (M) EDTA  = 1XV mg of CaCO3  =  x m.g of CaCO3
25 m.l water contains  =   x mg of CaCO3
1000 m.l water contains   =    x/25 X1000 m.g of CaCO3    =   y mg/l

The total hardness of water   =    y  mg/l


  • All the glass apparatus should be washed thoroughly with distilled water before use.
  • The burette should be rinsed with solution to be taken in it.
  • Inspect the burette carefully that there should not be any leakage.
  • The Conical flask should be placed  on white paper or broad  to identify the color changes. 

Information Civil

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