Determination of Total Hardness Of Water Using EDTA Method

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Hard water is usually detected by the “Total Hardness Of Water Using EDTA Method test”. Hard water is commonly defined as a type of water that requires a lot of soap to create foam or leather. Scale formation in boilers, heaters, and hot water pipes is caused by hard water. When the water goes through CaCO3 rock in the soil, it picks up CO2 from the atmosphere. These compounds make the water thick. Hardness is also caused by calcium and magnesium chlorides and sulfates.

Hardness is divided into two categories:

  • Permanent Hardness
  • Temporary Hardness

Permanent hardness is due to magnesium and calcium ions. When water passes through the soil, it removes carbonate ions. Carbonate ions are replaced by magnesium and calcium cations.

Temporary hardness results from dissolved bicarbonates of alkalinity that appear as the water evaporates or boils down. Temporary hardness increases with decreasing temperature and increasing pH.

The amount of hard water depends on the geology where you live. If there are more minerals, it will be harder to clean your clothes at home. Areas that have fewer rocks tend to have softer water because they don’t pick up much calcium when it goes through the soil.

Temporary Hardness:

Soft water contains some dissolved components that make the water more difficult to consume, such as Ca(HCO3) or Mg(HCO3), or both. It is also known as carbonate hardness since these chemicals dissolve in water to produce Ca2, Mg+2, and HCO3 ions, which cause hardness.

The hardness of water can be reduced by utilizing Clark’s technique, which entails adding limewater, Ca(OH)2 to the hard water.

The exudate (liquid portion) of magnesium carbonate and calcium carbonate is highly soluble in water. As a result, the two minerals settle to the bottom.

Permanent Hardness:

Noncarbonate hardness, also known as noncarbonate hardness or calcite hardness, is due to calcium chloride. The ion exchange method is used to remove permanent hardness caused by sodium zeolite, which is added to hard water. Because of this, calcium or magnesium zeolite is formed that is insoluble in water.

Disadvantages of hard water:

The hardness is determined using the following formula: (Final hardness reading – Initial reading) * 1000/50. The following statistics reflect the disadvantages of hard water:

  1. The amount of soap used increases.
  2. Boilers wear out quicker due to the formation of scales.
  3. If it is a MgSO2-containing compound, it can have a detrimental effect on the human digestive system.

W.H.O recommended hardness values for water:

The W.H.O hardness limit is 500mg/lit for CaCO3, which is in line with the NSPI recommended value of hardness.


Chemical required for Titration that are buffer solution Eriochrome Black T indicator and EDTA of standard normality e.g. 0.2, Conical Flask, Funnel, Burette, Sand, Beaker.


  1. Talke water sample of 50ml in a conical flask.
  2. Add 1ml of buffer solution (Buffer solution = Aluminum Hydroxide n Ammonium Chloride), which has a hardness of 1.
  3. Add 3 drops of ferrochrome or eriochrome black tea to the flask and mix well.
  4. Place the flask beneath the burette holding 0.02 normality of EDTA (Ethylene diamine tetra-acetic acid) solution.
  5. Close the tap on the burette and note the first reading of the burette. Allow the solution to flow in the flask by opening the tap on the burette.
  6. Note when the color of the water in the flask turns bluish.
  7. The final harness (temporary + permanent hardness) is calculated using the following formula.

Final hardness reading – Initial reading)* 1000/50


The World Health Organization (WHO) recommends 300mg/lit for CaCO3, which is lower than the NSPI recommended value of 500mg/lit for hardness.

Therefore it can be concluded that drinking hard water has no effect on humans because it will not harm people who drink hard water with a temporary hardness of 180-350mg/l according to the W.H.O but it may cause severe health problems if hardness is more than recommended values. One way around this problem is to use household filters that remove hardness ions from the water.

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