Complexometric titrations are specifically used to determine mixtures of different metal ions in solution. Typically, the endpoint of the complexometric titration is determined using a color-changing indicator such as eriochrome black T, calcein, etc.
Titration is a unique laboratory method for determining the concentration of an unknown analyte. Depending on the goals and procedures of the titration, it can be divided into four different types: acid-base, complexometric, precipitation, and redox titration.
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What is complexometric titration?
Complexometric titration, commonly known as chelatometry, is a volumetric analytical technique that uses a colored complex to detect the endpoint of a chemical reaction. It is the best way to find out how much of a certain type of metal ion is in a solution.
The metal ions in the sample react with the EDTA to form complexes, which can then be measured with standard acid. By measuring the endpoint of the titration, it is possible to the determination of the metal ions in the sample. Direct titration, back titration, replacement titration, and indirect titration are the types of complexometric titration.
The detection of endpoint in complexometric titration can be observed by two methods visual method or instrumental method.
Visual method:
Because of its precision and cost-effectiveness, it is the most used method. The techniques listed below are examples of the visual methods used to determine the endpoint of complexometric titrations.
- PM indicators or Metallochromic
- pH indicators
- Redox indicators
Instrumental method:
When using visual methods to find endpoints, there is a possibility that one will make a human error or be inaccurate. Consequently, some instrumental techniques are used in the determination of an endpoint.
- Photometry
- Potentiometry
- Miscellaneous methods
What is a complexometric indicator?
Complexometric indicators are water-soluble organic compounds that are also called pM indicators or metallochromic indicators. A complexometric indicator is an ionochromic dye that changes color in the presence of certain metal ions. It forms a weak complex with the ions in solution; its color is very different as compared to the form existing outside the complex.
Complexometric indicators are used in analytical chemistry to indicate the endpoint, it happens when all the metal ions in the solution are sequestered by a chelating agent(most usually EDTA). These indicators are also known as metallochromic indicators.
Example of complexometric indicator:
One of the most notable examples of a complexometric indicator is the Eriochrome Black T indicator. The indicator Eriochrome Black T is capable of displaying a wine-red color when bound to metal ions and a blue color when free from metal ions.
In an EDTA titration, the preferred blue endpoint is obtained when enough EDTA is added and the metal ions bound to the indicator are chelated by EDTA, leaving the free indicator molecule. When rare earth metals are present, Eriochrome Black T is employed to detect their presence. Therefore, a blue endpoint is obtained when it is used as an indicator in EDTA titrations.
List of indicators used in complexometric titration:
When determining metal ions by using reactions that form complexes, we always need a complexometric indicator to show us when the reaction is done.
Here are some common indicators used in complexometric titration are some of the names are,
- Eriochrome Black T or Solochrome Black T (Ethylenediaminetetraacetic acid):
Appearance: Brownish black powder
- Thymolphthalein complexone:
Appearance: White to off white
- Xylenol orange:
Appearance: Red brown to dark brown
- Hematoxylin:
Appearance: Light to dark-brown
- Ammonium purpurate or Murexide:
Appearance: Dark red to purple powder
- Bromopyrogallol red:
Appearance: Brownish red color
- Calcein (fluorescent metal indicator):
Appearance: Yellow to orange brown crystalline
- Calmagite:
Appearance: Brownish black
- Dithizone:
Appearance: Black
- Murexide:
Appearance:Dark Red to Purple
- Patton-Reeder Indicator (Calconcarboxylic acid):
Appearance: Dark purple to black powder
- Curcumin:
Appearance: Yellow
- Fast Sulphon Black:
Appearance: Grey to Black Solid
The following are some frequently asked questions about complexometric titration indicators:
Which indicators are used in complexometric titration?
Eriochrome black T, fast sulphon black, murexide, calcein, and eriochrome red B, etc. are the indicators used in the complexometric titration.
Which type of indicator is EDTA?
EDTA (ethylenediaminetetraacetic acid) is a type of complexometric indicator composed of two amino groups and four Lewis bases (carboxyl groups).
Why buffer solution used in EDTA titration?
Because it resists pH changes, a buffer solution is employed in EDTA titration. since all reactions involving metal ions and EDTA are pH-dependent.
What is a pM indicator?
It is a dye that acts as a chelating agent. This makes a dye-metal complex that looks different from the original dye and is less stable than the corresponding chelate-metal complex.
People also ask:
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