Water Analysis : To Estimate Calcium Hardness of Water

AIM: TO ESTIMATE CALCIUM HARDNESS OF WATER

PRINCIPLE:

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)₂ 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 ]

REQUIREMENT:

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

PROCEDURE:

-          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 CaCO₃ (mg/l)

1.    Ca as CaCO₃ mg/l =  ( C * 400.8)/ ml of Sample

2.    Ca hardness as CaCO₃ mg/l  =  ( C * 1000 * X) / ml of Sample