Q. Name of the reagent required for determination of hardness of water sample of complex metric method. Briefly give the function of each reagent used.

Ans. Reagents required for determination of hardness of water sample by complex metric method:

(1)         Standard water sample: To determine the strength of unknown EDTA solution.

(2)         EDTA solution: It is a strong complexing agent. It acts as a tetra dentate or hexa dentate legend and binds with metal ions to give colourless and very stable chelate.

(3)         Buffer solution of pH-10: It is prepared by mixing 67.5 ml of NH₄Cl and 570 ml of concentrated ammonia and make up to one Litre with distilled water. It maintains the pH-10 Erichrome black-T work at pH-10.

Indicator solution (Erichrome black-T): It has two ionisable phenol hydrogen atoms. It gives wine red coloured unstable complex with Ca⁺² and Mg⁺² ions of hard water.