Determining The Hardness Of Water By Complexometric Titration

Complexometric Titration 

Here,in this experiment we will determine the hardness of water sample complexometrically using EDTA.

Natural water (surface and ground) generally contains dissolved minerals. When soluble salts of calcium and magnesium are present in it then it is said to be hard water. Hard water should be used for drinking purposes while soft water is used for industrial and domestic purpose. If hard water is used in industries it causes scale formation in the boiler and also corrodes it. In both conditions, it reduces the life time of the boiler thereby increases the chances of industrial accidents. So it is very important to know alkaline the amount of hardness and its type present in water. Quantitatively, it is determined by complexometric method using EDTA. In this method, the titrant, EDTA (Ethylene- diamine tetra acetic acid) binds with Ca+² and Mg^+2 ions present in hard water and form a complex compound. The metal ion is called central metal ion and EDTA is known as ligand, the complexing agent.

Water which consumes considerable amount of soap to produce lather or foam is known as hard water. Hardness is defined as soap consuming capacity of water due to presence of calcium, magnesium ions which react with soap to form precipitate. Hardness of water is caused by the presence of bicarbonates, chlorides and sulphates of calcium and magnesium. On the basis of salts present in water, the hardness of water is classified as (i) Temporary and (ii) Permanent hardness.

  

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(i) Temporary hardness: It is due to the presence of bicarbonates of calcium and magnesium, which can be removed by boiling.

(ii) Permanent hardness: It is due to the presence of sulphates and chlorides of calcium and magnesium which cannot be removed by simple boiling. The total hardness (Temporary and Permanent) can be determined by complexometric titration using EDTA, in presence of EBT as an indicator. Permanent hardness can be determined by removing temporary hardness (converting bicarbonates into insoluble carbonate ) by boiling followed by titration with EDTA.

 Temporary hardness = Total hardness -  Permanent hardness     

 

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