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COMPLEXOMETRIC TITRATION
Complexometric Titration or chelatometry is a type of volumetric analysis wherein the colored complex is used to determine the endpoint of the titration. The method is particularly useful for determination of the exact number of a mixture of different metal ions, especially calcium and magnesium ions present in water in solution .
In this type of titration a standard solution or reagent also called titrant e.g. EDTA is used to titrate against unknown analyte. With each drop of titrant being added, the reaction eventually reaches an equilibrium state. The equivalent point can be identified very accurately using any of the following two methods.
- 1. Visual Method
This is one of the most common methods for determination of endpoint owing to its simplicity, least cost and accuracy. Following are some of the visual methods used for determining the end point of the complexometric titrations.
- Metallochromic or PM indicators
- pH indicators
- Redox indicators
- Instrumental Method
This utilizes some instrumental techniques including;
- Photometry
- Potentiometry
- Miscellaneous methods.
Indicators
Calmagite and Eriochrome BlackT (EBT) are such metallochromic indicators that change color from blue to pink when they complex with metals such as calcium or magnesium. The endpoint of a complexometric EDTA titration using either Calmagite or EBT as the indicator is detected as the colour changes from pink to blue.
Besides EDTA ,there are also other similar chelating agents (EGTA, CDTA and so on) used. In some of other methods AgNO3 is used as a titrant for determining cyanides and Hg2+ as a titrant in Cl– determination.