Complexometric titration is a type of volumetric analysis in that the formation of a colored complex is employed to determine the end-point of the titration. It is primarily used to quantify metal ions by employing complex-formation reactions.
Titration is the most common quantitative and volumetric laboratory technique used to determine the unknown concentration of a solute by comparing it with the known concentration of a solution in the presence of an indicator.
There are different types of titration when considering goals and processes such as acid-base titrations, redox titrations, precipitation titrations, and complexometric titrations are used, however, redox titration and acid-base titration are the most used types of titration in quantitative chemical analysis.
The required apparatus for titration consists of the beaker, conical flask, funnel, burette, pipette, burette stand, wash bottle, etc. generally they are inexpensive.
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What is a complexometric titration give example?
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.
The determination of water hardness using EDTA with Eriochrome black-T as the indicator is one example of complexometric titration.
Principle of complexometric titration:
When the indicator Eriochrome Black T binds with metal ions, it turns wine-red, however, when it is free from metal ions, it remains blue in color. While ethylene diamine tetraacetic acid (EDTA) is colorless regardless of whether it is coupled or not to a metal ion.
As Eriochrome black T binds to metal ions, adding an EBT indicator to the sample turns it wine-red in color. Eriochrome Black T has loosely binds with metal ions, whereas EDTA has strongly bound with metal ions. Therefore, when all the metal ions are bound to EDTA, the EBT indicator in the sample solution remains free and the solution appears blue.
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.
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.
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.
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.
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.
Applications of complexometric titrations:
- The complexometric titration is used to determine the concentration of metal ions in sample solutions.
- It is used for the estimation of the amount of calcium present in food products.
- It is used to find out the total hardness of the water.
- Complexometric titration is commonly used in the pharmaceutical industries to determine the concentration metal is in a pharmaceutical dosage form (Drug).
- It is used in analytical chemistry to perform the assay.
- Complexometric titration is used in environmental analysis to determine bad metals.
- Cosmetic products are also analyzed by complexometric titration.
Which indicator is used in complexometric titration?
Complexometric indicators are water-soluble organic molecules that play an important role in the titration to indicate the endpoint. These indicators undergo a certain color change in the presence of specific metal ions. Commonly used indicators in complexometric titration are organic dyes which are organic molecules that are soluble in water. When the endpoint is achieved, a color change indicates that the indicator has been displaced from the metal cations in the solution.
Examples of complexometric indicators are Eriochrome Black T, calgamite, arsenazo, xylenol orange, Eriochrome red B, fast sulphon black, and calcein, etc. Eriochrome Black T, which acts as an acid/base indicator as well as a metal ion indicator, is the most often used indicator in complexometric titration.
Methods of endpoint detection in complexometric titration:
The endpoint of the complexometric titration is detected by two methods i.e. visual method and the instrumental method.
Visual method:
The visual method is one of the most popular ways for determining endpoints, because of its advantages, simplicity, cost-effectiveness, and precision. It consists of metallochromic/PM indicators, pH indicators and redox indicators.
Instrumental method:
The instrumental method is also used for determining endpoints of the practical. Instruments are used for complexometric titration such as photometry and potentiometry etc.
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