Hardness may range from zero to hundreds of milligram per liter in terms of calcium carbonate, depending on the source of water and due to the presence of the following cations such as Ca^2+, Fe^2+, Sr^2+, Zn²⁺, Mn²⁺, and Mg²⁺ but the cations Ca²⁺ and Mg²⁺ are the only cations which are at higher concentration.  The reason why the hardness is considered as the summation of those two cations (Ca²⁺ and Mg²⁺).

Therefore, Total Hardness (TH) = [Ca²⁺] + [Mg²⁺]

Apparatus and Reagent

·         Volumetric flask,

·         conical flask, burette,

·         pipette,

·          measuring cylinder,

·          burette

·         stand,

·          wash bottle

·         Buffer solution-

·         Eriochrome Black T solution (as indicator)

·         Standard EDTA titrant (0.01M)

·         Standard calcium solution-

Procedures

Ø  Standardize the EDTA titrant against standard calcium solution

Ø  Take 50 ml sample in a conical flask add 2 ml buffer solution and 2 drops EBT indicator solution, wine red colour appears.

Ø  Titrate with EDTA till the color changes to blue.

Ø  Note the volume of EDTA used and Calculate the total hardness by following formula

 Total Hardness (EDTA) mg/l= A x B x 1000/ volume of sample

Where

A= ml EDTA used 

B= mg CaCO3 equivalent to 1 ml EDTA

References

1.      Sadhana C.; Ananda Dev G.; Handbook of Water, Air and Soil Analysis; a Lab Manual; International-E-Publication;2014

2.      Frank R.Spellman; Handbook of water and wastewater treatment plant operations; Lewis publishers;2003

3.      Leena Deshpande;Water Quality Analysis Laboratory methods; New Delhi; India.