AIM: 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)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 ]
- 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.
- 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 Sample2. Ca hardness as CaCO₃ mg/l = ( C * 1000 * X) / ml of Sample