Complexometric method

(EDTA METHOD)
By : SHREE RAM SHARMA

Principle
Ca+2/Mg+2 + EBT [Ca+2—EBT]
(Wine Red colour/Less stable)
Ca+2/Mg+2 + EDTA [Ca+2—EDTA]
(Colour Less/More stable)
[Ca+2—EBT] [Ca+2—EDTA] + EBT
(BLUE COLOUR)

Procedure
 Preparation of Solution
 Determination of Hardness of Water
 Calculation

Preparation of Solution
I. EDTA Solution
II. EBT Solution
III. Buffer Solution
IV. SHW Solution

Determination of Hardness
 Standardization of EDTA :
10ml SHW + 3ml Buffer + 2 drop EBT
wine red colour
+EDTA
Blue colour
(End Point)

 Determination of Total Hardness :
10ml Water Sample +3ml Buffer + 2 drop EBT
wine red colour
+EDTA
Blue colour
(End Point)

 Determination of Permanent Hardness :
250ml Water Sample boil 50 ml filter Filtrate
make up to 1 lt. by D.W.(Boil Water)
10ml boil water sample + 3ml Buffer + 2 drop EBT
Blue colour +EDTA wine red colour
(End Point)

Calculation
 Standardization of EDTA :
10 ml of SHW = 10mg of CaCO3 eq.
10 ml of SHW = V1 ml of EDTA
10 mg of CaCO3 eq. = V1 ml of EDTA
1 ml of EDTA = 10/ V1 mg of CaCO3 eq.

 Total Hardness :
10 ml H2O sample = V2 ml of EDTA
10 ml H2O sample = V2×10/V1 mg of CaCO3 eq.
1000 ml of H2O sample = (V2/V1)×1000 ppm

 Permanent Hardness :
10 ml boil H2O sample = V3 ml of EDTA
10 ml boil H2O sample = V3×10 mg of CaCO3 eq.
1000ml of boil H2O sample = (V3/V1)×1000 ppm

 Temporary Hardness :
Total Hardness = Temp. H. + Per. H.
Temp. H. = Total H.-Per. H.
=> Temp. H. = {(V2-V3)/V1}×1000 ppm

Advantages
 Greater accuracy
 More rapid procedure
 Convenience

Complexometric method

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