Geo-Scientist Prelims 2025 Chemistry Q39: In order to determine the amount of Ca²⁺ through complexometric…

In order to determine the amount of Ca²⁺ through complexometric titration with EDTA using Eriochrome black T, which one of the following may be adapted to obtain a sharp end point ?

1. (a) A sufficiently large amount of free Mg²⁺ should be added to Ca²⁺ solution
2. (b) A small measured amount of free Mg²⁺ should be added to Ca²⁺ solution
3. (c) Addition of Mg²⁺ is not at all required as it will hinder with the formation of Ca-EDTA complex by making Mg-EDTA complex
4. (d) Both (a) and (b) are correct as Mg²⁺ is required to initiate the complexation reaction failing which EDTA remains unreacted