Date : 28/03/2022
Aim: To estimate the amount of total hardness present in the given sample of water by EDTA
titration method.
Apparatus required: 50 ml Burette, 20 ml Pipette, 250 ml Conical flask, 100 ml Beaker, 250 ml
beaker, Glass funnel.
Reagents: EDTA solution, Standard CaCO3 solution, Eriochrome BlackT indicator, Buffer
solution.
Theory: EDTA (Ethylenediamine tetra acetic acid) forms colorless stable complexes with Ca2+
and Mg2+
ions present in water at pH = 9-10. To maintain the pH of the solution at 9-10, buffer
solution (NH4Cl + NH4OH) is used. Eriochrome Black-T (E.B.T) is used as an indicator.
The sample of hard water must be treated with buffer solution and EBT indicator which forms
unstable, wine-red colored complex s with Ca2+ and Mg2+ present in water .
Procedure
1. Standardization of EDTA
(i) Pipette out 20 ml of standard hard water into a conical flask.
(ii) Add 5 ml of buffer solution and few drops of Eriochrome Black-T. The indicator, which is
originally blue color would acquire a wine-red color.
(iii) Titrate with EDTA solution taken in the burette, till the wine red color changes to blue
which is the end point. Let the burette reading of EDTA be V2 ml.
2. Determination of Total hardness
Repeat the above titration method for sample hard water instead of standard hard water. Let the
burette reading of EDTA be V3 ml.
3. Determination of Permanent hardness
Take 100 ml of sample hard water in 250 ml beaker. Boil it to remove temporary hardness to
about half of this volume and cool to room temperature. Filter through filter paper to remove
insoluble CaCO3 and MgCO3. Make up the volume to the original 100 ml by adding distilled
water. Now pipette out 20 ml of this solution into a clean conical flask. Then repeat the process
of titration steps as mentioned above. Let the burette reading of EDTA be V4 ml.
Observations :
| Data | Burette Reading ( ml ) |
| V1 ( Volume of standard hard water in conical flask ) | 20 ml l |
| V2 ( Volume of EDTA consumed ) | 27.7 ml |
| V3 ( Volume of sample hard water in conical flask) | 3.4 ml |
| V4 (Volume of sample hard water in conical flask ) | 3.1 ml |
.
- Calculations1. Standardization of EDTA
- M1V1 = M2V2
- Where, M1 = Molarity of standard hard water = 0.002
- V1 = Volume of standard hard water in conical flask
- M2 = Molarity of EDTA = 0.001
- V2 = Volume of EDTA consumed (burette reading)
- . Determination of Total hardness
- M2V2 = M3V3
- Where, M3 = Total hardness of sample water =0.0081
- V1 = Volume of sample hard water in conical flask3.
- Determination of Permanent hardness
- M2V2 = M4V4
- Where, M4= Permanent hardness of sample water = 0.0089
- V4 = Volume of sample hard water in conical flask.
- Determination of Temporary hardness
- Temporary hardness = Total hardness – Permanent hardness = 0.0081 – 0.0089 = 0.0008 x 10 5 = 80 ppm
- Result: The hardness of the given water sample
- Total hardness = 81 ppm
- Permanent hardness = 89 ppm
- Temporary hardness = 80 ppm
