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Finding Total Hardness Of Water Using EDTA Method



Hard water is generally considered to be one which requires considerable amount of soap to produce foam or leather. Hard water cause scale formation in boilers heaters and hot water pipes. The rain water catches CO2 from the atmosphere when the water pass through CaCO3 rock in the Soil, these compounds make the water hard. Calcium and magnesium chlorides and sulphates also cause hardness

There are two types of hardness:

  1. Temporary Hardness
  2. Permanent Hardness

Temporary Hardness:

This type of hardness is mostly caused by Ca(HCO3) or Mg(HCO3) OR both, therefore it is also called carbonate hardness, these compounds dissolve in water and form Ca2, Mg+2 and HCO3 ions which cause hardness

H2O+ CO2--> H2CO3

CaCO3 + H2CO3 --> Ca(HCO3)2

Temporary hardness can be removed by Clark's method by adding limewater,Ca(OH)2 to the hard water.

Ca(HCO3)2 + Ca (OH)2 -->2CaCO3 + 2H2O
Mg (HCO3)2 + Ca (OH)2 --> Mg CO3 + CaCO3 + 2H2O

As the magnesium carbonate and calcium carbonate are insoluble in water and settles down,

Permanent Hardness:

It is also known as non carbonate hardness and it is caused by CaCl2.MgCl2, CaSo4 and MgSO4, the ion exchange method is used for the removal of the permanent hardness sodium zeolite is added to hard water due to which calcium or magnesium zeolite is formed which is insoluble in water.

Ca + 2Na (zeolite) --> Ca (Zeolite ) + 2Na + 2

Disadvantages of hard water:

Total hardness = (Final hardness reading - Initial reading) 1000/50. The following values give the type of hard water:

Hardness mg/lit as CaCO3 Hardness (mg/lit Type of water
0 - 75 Soft water
75 - 150 Moderately hand water
150 - 300 Hard water
above 300 Very hard water

W.H.O guideline values:

W.H.O guideline value of hardness is 500mg/lit as CaCO3

  1. Greater amount of soa is used.
  2. Scale formation reduces the life of boilers.
  3. Effect the digestive system of it contains MgSO2


  • Conical Flask
  • Funnel
  • Burette
  • Sand
  • Beaker


Buffer solution of hardness ferrochrome black tea EDTA solution of 0.02normality.


  1. Take 50ml of water sample in conical flask.

  2. Add 1ml of buffer solution (Aluminum Hydroxide n Ammonium Chloride) of hardness1.

  3. Add 3 drops of ferrochrome black tea to the flask and shake well.

  4. Place the flask below the burette containing EDTA (Ethylene diamine tetra-acitic acid) solution of 0.02 normality.

  5. Note the initial reading of the burette and open the tape of the burette to allow the solution to flow in the flask.

  6. Note The Final Reading when the color of the water in the flask turn bluish.

  7. The total harness (temporary + permanent hardness) is found by using the following formula.


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