Complexometric titration :-
Complexometric titration is also known as chelatometry. Volumetric titrations or analysis in which the endpoints are specified by colored compounds are known as complexometric titrations.
In complexometric titrations an indicator is used that can produce a clear color change in the titration, indicating the titration's endpoint or equivalance point which is dependent on the formation of a complex between the analyte and the titrant. It is very useful for determining the concentration of a mixture of metal ions in the sample solution.
Types of complexometric titration :-
As a chelating titrant, the ethylene diamine tetraacetic acid (EDTA) can be used in different ways. Hence the titrations with EDTA can be performing in different types some of them are as follows.
1) Direct titration method :-
The direct titration method is similar to the acid-base titration technique and is simple and convenient. In this method, the standard EDTA solution is gradually added using a burette to the metal ion solution until the desired endpoint is reached.
Direct titration is used to determine the copper, mercury, zinc, barium, chromium, aluminum, and lead, etc. in which the solution containing the metal ion to be measured is buffered to the required pH and directly titrated with a standard EDTA solution.
2) Back titration method :-
A back titration is a type of complexometric titration in which the analyte concentration is determined by reacting with a known amount of excess reagent. Metal ions that cannot be directly titrated with EDTA are determined using the back titration method.
3) Replacement titration method :-
The replacement titration method is used when direct titration or back titration fails to produce sharp endpoints. The metal ion is determined by displacing zinc or magnesium ions from an EDTA complex with an equivalent number of metal ions, then titrating the liberated Zn or Mg ion with a standard EDTA solution.
4) Indirect titration method :-
The indirect titration method is commonly used when normal titrations are slow, or the endpoint is difficult to determine, as well as in other applications such as weak acid-weak base reaction. Some anions (For example barium ions) precipitate when they come into contact with metal cations, and these anions do not react with EDTA. Hence, indirect titration with EDTA can be used to determine these types of compounds.
