What is Hard Water?

The water which gives low or no froth with soap and detergent is known as hard water. Hard water is due to the presence of bicarbonates, sulphates, chlorides, nitrates of calcium and magnesium.

Hard water is of two types

Temporary hardness: Temporary hardness of water is due to the presence of bicarbonate of calcium and magnesium in the water. It can be easily removed by simply boiling water. Calcium bicarbonate and magnesium bicarbonates are converted into carbonate forms which settle down.

                Ca(HCO3)2 ———> CaCO3 ↓ + H2O + CO2

              Mg(HCO3)2 ————> MgCO3  +   H2O   +  CO2

Permanent hardness: Permanent hardness is due to the presence of sulphate, chlorides, nitrates of calcium and magnesium. Such water can’t be removed by boiling and advanced methods are applied. First of all total hardness of water is determined by titrating with EDTA and then permanent hardness is determined by the same method. Temporary hardness is determined by subtracting the amount of permanent hardness from total hardness.

Determination of total hardness

Both temporary and permanent hardness of water is determined by complexometric titration using EDTA (ethylene diamine tetraacetate) as a complexing agent in the presence of the solochrome black T indicator.

For total hardness: For determination of total hardness of water, a sample of 50 ml cold water is titrated with EDTA by using solo chrome black T prepared in the basic buffer solution till wine red color changes into clear blue color.

S.NVol. of waterVol. of EDTA(Burrette readingConcurrent reading
Initial Final Different
1 50 ml        
2 50 ml        
3 50 ml        

Effect of hard water

  1. Soap and detergents do not give froth properly.
  2. It corrodes water pipe, metallic pots
  3. It fads the color of clothes, mats, etc.
  4. Also, it affects and can damage the human body parts such as the kidney, liver.
Effect of Hard Water on tap
Effect of Hard Water On Water Tap Surface

Also Read: Chemical Oxygen Demand (COD) AND Dissolved Oxygen (DO)

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