Page 54 - Statistics presented by Dr. Sara Ismail Aborass

9/8/2023

Classification of water :

Waters are commonly classified in terms of the degree

of hardness.

(1 Degree = 1 mg CaCO3/l) :

(1) Soft water : 0-75 ppm or (mg/l)

(2) Moderately hard water : 75-150 ppm

(3) Hard water : 150-300 ppm

(4) Very hard water : 300 ppm or more

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DETERMINATION OF WATER HARDNESS:

EDTA method
* For total Ca and Mg contents :

Buffer water sample to pH 10 using
NH4Cl/NH4OH, then titrate with st. EDTA using
E.B.T. indicator.

* For calcium hardness alone :
Buffer to pH 12, titrate against st. EDTA using
murexide indicator.

* Mg hardness is measured by difference.

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