Total Hardness testing method:
The method is based on the reaction of calcium and magnesium salts with ethylenediaminetetraacetate (EDTA); Erichrome black T is used as the indicator.Reagents:
Erichrome black T solution:
– dissolve 0.5g of Erichrome black T in 100ml of triethanolamine
Buffer solution:
– dissolve 40g of borax in approximately 800ml of distilled water. Dissolved 10g of NaOH, 10g of sodium potassium tartrate and 5g of sodium sulphide in 100ml of distilled water. When cool, mix the two solutions and dilute to1000ml with distilled water. The reagent should not be used for more than one month after preparation.
Standard EDTA solution:
– (0.02N) In 1liter round bottom flask dissolve 3.72g of disodium ethylenediaminetetraacetate dihydrate in water and fill it up to the mark.
Procedure:
Measure 50ml of the sample into a 250ml conical flask. Add 2 to 3 drops of indicator sol and mix add 0.5ml of buffer solution and mix. Titrate immediately with EDTA solution with continues mixing until the colour changes from red to blue. As the endpoint is approached, the sol shows some blue colourations but a definite reddish tinge and is discharged at the endpoint.
Calculation:
Total hardness (as CaCO3), mg/l= 1000×V1/V2
Where
V1= volume in ml of Std EDTA sol consumed, and
V2= volume in ml of the sample taken for the test
For other methods of volumetric analysis