Titration, also known as titrimetry and volumetric analysis, is a chemical qualitative analysis technique that is used to determine the unknown concentration of an identified analyte. In the process of titration, an analyte and a titrant are used. To find the endpoint of titration for analysis, a known concentration of titrant is added to an unknown quantity of analyte.
When the endpoint is reached, the moles of titrant and analyte will be identical. Titration can be divided according to its processes and goals, acid-base titration, complexometric titration, precipitation titration, redox titration, etc.
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What is complexometric titration?
Complexometric titration also called chelatometry used to determine the metal ions n a solution. It is a type of volumetric titration wherein the colored complex is used to determine the endpoint of the titration. In this kind of titration, an indicator is used that can cause a clear change in color in the titration, which shows the endpoint of the titration.
In complexometric titrations, a metal-ligand complexation reaction is used. It is based on the formation of a complex between the analyte and the titrant. It is a common method to titrate metal ions in a solution using the chelating agent EDTA.
One example of complexometric titration is the process of determining the hardness of water by titrating it with EDTA while using eriochrome black-T as the indicator. For complexometric titrations in analytical chemistry, EDTA (Ethylenediaminetetraacetic acid) is one of the most often employed chelating agents.
What is the principle of complexometric titration?
The principle behind complexometric titrations is the transformation of a simple ion into a complete ion to determine the endpoint using a metal indicator and the displacement of water from the solvation sphere of the metal ions by ligands.
When EBT binds to metal ions, it turns a wine-red color. Though, when it is not bound to metal ions, it remains blue. While EDTA is colorless regardless of whether it is coupled or not to a metal ion.
What are the indicators used in complexometric titration?
Complexometric indicators are the indicators used in complexometric titrations. When particular metal ions are present, the color of these indicators changes significantly. These are also referred to as metallochromic indicators or PM indicators.
These indicators are water-soluble organic molecules. Some complexometric indicators are Eriochrome Black T, calcein, fast sulphon black, hematoxylin, Curcumin, etc.
Examples of indicators that turn pink when calcium or magnesium is present are Calmagite and Eriochrome Black-T. A complexometric EDTA titration using either Calmagite or EBT as the indicator reaches its endpoint when the color changes from pink to blue.
What is the classification of complexometric titration?
Ethylene diamine tetra acetic acid (EDTA) can be used as a chelating titrant in several ways. Consequently, EDTA titrations can be performed in a variety of ways, as follows.
Direct titration:
Direct titration is the most practical and easy method of EDTA isometric titration. It is similar to the acid-base titration technique. To provide a sample with metals, the EDTA solution is added to the titration standard. This sample is then titrated until the endpoint is reached. Direct complexometric titration can be used to identify a variety of metals including zinc, copper, aluminum, barium, lead, mercury, bismuth, chromium, etc.
Back titration:
Because we are titrating for the excess amount of EDTA, this is known as back titration. An excess of EDTA standard solution is added to the metal solution. The excess EDTA is then back titrated with the solution of the second metal ion.
Replacement titration:
Substitution titration is used when direct titration or back titration fails to produce sharp endpoints. The metal–EDTA complex receives this analyte; the metal present in the analyte displaces another metal from the metal-EDTA complex.
Indirect titration:
Certain anions react with metal cations to form a precipitate. EDTA does not affect these anions. Consequently, indirect titration with EDTA can be employed to analyze these substances. Indirect titration can be used to determine barium ions.
Key terms used in complexometric titrations:
- Burette: A graduated glass tube having a tap at one end is used for titration to administer known volumes of liquid.
- Analyte: A substance whose quantity/concentration is to be determined.
- Titrant: A solution with a known concentration is filled in the burette that is added to another solution to find out the concentration of a second chemical species.
- Buffer: A solution consisting of an acid and its conjugate base is used to control the pH of a solution.
- pH: A measure of the hydrogen ion concentration is equal to - log [H+].
- Complex: a substance composed of two or more components capable of independent existence.
- Metal chelate: a species that is simultaneously bound to two or more sites on a ligand.
- Complexing agent or ligand: molecules and/or anions with one or more donor atoms that each donate a lone pair of electrons to the metal ion to form a covalent bond.
- Chelation: the process involved in the formation of a chelate.
- Chelating agents: organic molecules containing two or more donor groups that combine with metal to form a complex are having a ring structure.
Frequently Asked Question (FAQ):
What are the methods of endpoint detection in complexometric titration?
In a complexometric titration, there are two ways to identify the endpoint: visual technique and instrumental techniques.
Why eriochrome black t is used in complexometric titration?
In complexometric titrations, the eriochrome black T is used as an indicator because it forms a colored complex in its protonated form with calcium, magnesium, or other metal ions. In the process, its color shifts from blue to pink and red.
What is the role of buffer solution is used in EDTA titration?
All reactions between metal ions and EDTA are pH-dependent, so a buffer solution is used because it is resistant to pH changes. Ammonium chloride and ammonia buffer (NH4Cl + NH4OH buffer) buffer solution of pH 10 is used in EDTA titration to determine the hardness of the water.
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