The reagent commonly used to determine hardness of water titrimetrically is

Step-by-step solution

Disodium salt of ethylene diamine tetracetic acid has been used for the estimation of M²⁺ metal ions like Mg ²⁺, Ca ²⁺ etc. by complexometric titrations. In this titration, indicator ions ( D³⁻ ions) form redmetal indicator complex, [M D⁻ ] with M²⁺ ions. array ccc (i) M²⁺+ & D³⁻ pH =10 & [M²⁺ D ]⁻ metal ion & indicator & Metal indicator ( Mg ²⁺ or Ca ²⁺ ) & ion (blue) & complex (red) (ii) [M²⁺ D ]⁻+ & EDTA ⁴⁻ & [M²⁺( EDTA ) ]²⁻+D³⁻ (red) & EDTA ion & metal-EDTA & & complex array The release of the free indicator i