Question

The reagent commonly used to determine hardness of water titrimetrically is:

• A. Oxalic acid
• B. Disodium salt of EDTA
• C. Sodium citrate
• D. Sodium thiosulphate
• E. None of these

Answer 1

Answer: (B)

Disodium salt of EDTA

The total hardness of water (i.e. the concentration of dissolved cations such as $C{a}^{2+},M{g}^{2+},F{e}^{3+}$ etc.) is commonly determined by the titration of a water sample with a standardized solution of the disodium salt of ethylenediaminetetraacetic acid (EDTA) using eriochrome black T or calmagite as an indicator. Calmagite has the advantage of forming indefinitely stable solutions and will be substituted without any other modification to the procedure.
Hence option B is correct.