Sunday, 15 May 2016

Water Analysis : To Estimate Calcium Hardness of Water

When addition of EDTA is applied to water containing both Ca & Mg, it combined with Ca first. Ca can be determined directly by EDTA when the pH is sufficiently high, Mg(OH) and the indicator is used that combines with only calcium murexide indicator give a color change from pink to purple. When all the Ca has been complexed by EDTA at pH 12 to 13

  • WHO(1963): 75mg/l as maximum acceptable

  •  ISO(10500:1991): 5mg/l as maximum permissile ]


  •  8% NaOH solution
  • Mururide indicator: ammonium purpurate = 0.2gm
  • NaCl  = 100gm
  • Std EDTA solution (0.01m)
  • EDTA = 3.723 gm + 1000 ml D/W

-          Take 25 ml of sample and dilute to 50ml by using D/W
-          Add 1ml NaOH to rise the pH to 12 to 13.
-          Add a pinch of murexide indicator.
-          Titrate  immediately by slandered EDTA till pink color changes to purple. Note down the volume of  EDTA.
-          Run a reagent blank and note down with used that (B).
-          Calculate the amount of EDTA required by sample (C = A – B)
-          Use the following formulae and calculate the concentration of Ca (mg/l) and Ca hardness  as CaCO (mg/l)
1.    Ca as CaCO mg/l =  ( C * 400.8)/ ml of Sample
2.    Ca hardness as CaCO mg/l  =  ( C * 1000 * X) / ml of Sample

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