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The hardness of a water sample is measured directly by titration with 0.01 M solution of ethylenediamine tetraacetic acid (EDTA) using eriochrome black T (EBT) as an indicator. The EBT reacts and forms complexes with divalent metallic cations present in the water. During titration, the EDTA replaces the EBT in the complex. When the replacement of EBT is complete at the end point of the titration, the colour of the solution changes from

The hardness of a water sample is measured directly by titration with 0.01 M solution of ethylenediamine tetraacetic acid (EDTA) using eriochrome black T (EBT) as an indicator. The EBT reacts and forms complexes with divalent metallic cations present in the water. During titration, the EDTA replaces the EBT in the complex. When the replacement of EBT is complete at the end point of the titration, the colour of the solution changes from Correct Answer wine red to blue

Explanation

The hardness of water is defined as the concentration of multivalent metallic cations which destroys the surfaced property of soap (Concentration of ions) which reacts with Soap and leads to the formation of a precipitate.

Ca 2+, Mg2+ are major constituents

Al+3, Sr3+, Fe2+ Cu2+ are minor constituents of hardness.

Hardness is classified into two categories:

Carbonate hardness and non-carbonate hardness

Total Hardness (TH) = Carbonate Hardness (CH) + Non-Carbonate Hardness (NCH)

  • Hardness in water can be determined by the determination of amounts of calcium and magnesium ions present in water by filtration
  •  Amount of Ca 2+, Mg2+ is determined by titration with versanate solution ( EDTA Method)
  •  In the EDTA method water is titrated with ethylene diamine tetraacetic acid using Erichrome Black T (EBT) as an indicator.
  •  EBT forms wine red colour and titration changes the colour to blue.

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