Replacement or Substitution Titrations

According to the principle of these titrations, the metallic ion to be titrated Mi displaces a metallic ion Mu from its complex already formed with EDTA, namely, [MiiY]  

29 Complexometry III Metal Cation Indicators tind Types of EDTA Titrations 

4 Substitution titration of a metallic ion Mi by displacement with the MnY complex 

For this sort of titration to occur satisfactorily, the MjY complex must be more stable than the MnY complex in the experimental conditions, that is. 

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C. Replacement or substitution titration. Substitution titrations may be used for metal ions that do not react (or react unsatisfactorily) with a metal indicator, or for metal ions which form EDTA complexes that are more stable than those of other metals such as magnesium and calcium. The metal cation M + to be determined may be treated with the magnesium complex of EDTA, when the following reaction occurs ... 

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