Question

Which of the following method is used to estimate the hardness of water?

• A. conductivity method
• B. EDTA method
• C. titrimetric method
• D. distillation method

Answer 1

Answer: (B)

EDTA method

The hardness of water can be determined by complexometric titration using Ethylene diamine tetraacetic acid (EDTA). EDTA in the form of its di-sodium salt forms complex with $C{a}^{2+}$ and $M{g}^{2+}$ ions of the water sample.

When Eriochrome Black T (EBT) indicator is added to the hard water at pH around 9.10, it gives wine red coloured unstable complex with $C{a}^{2+}$ and $M{g}^{2+}$ ions of the water sample.