Titration is a laboratory technique used to estimate the concentration of an unknown analyte. It is classified into four types based on their goals and procedures: acid-base, complexometric, precipitation, and redox titration.
Complexometric titration, also known as chelatometry, is a volumetric analytical method that detects the endpoint of a chemical reaction by using a colored complex. It is the most precise way to find out how much of a certain metal ion is in a sample solution.
The EDTA reacts with the metal ions in the sample to form complexes, which can then be measured using standard acids. It is possible to identify metal ions in a sample by determining the endpoint of the titration. There are two ways to observe the complexometric titration endpoint: the visual method and the instrumental method. The several types of complexometric titration include a direct, back, replacement, and indirect titration.
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What is a metal ion indicator?
A metal ion indicator is a substance used in analytical chemistry that changes color when it binds to metal ions in a solution. Metal ion indicators are usually polyprotic complexing agents that are used to indicate the endpoint in the titration.
Generally, an indicator is a substance that can be added to the reaction mixture to show the equivalence or endpoint point of the titration. In different pH solutions, an acid-base indicator changes color to tell us when an acidic solution has turned into a basic solution. An indicator for redox titration will change color either when all of the reactants have been used up or when there is still excess titrant remaining.
A metal ion indicator would also require a color change to indicate the presence of metal ions. For example, ferrous (Fe2+) ions form a complex with ferricyanide to produce Prussian blue. The ferricyanide can be employed as an indicator in a reaction that generates ferrous ions. When ferrous ions are formed, the solution turns blue; when they are used up, the solution becomes colorless.
What is an example of a metal ion indicator?
A good example of a metal ion indicator is xylenol orange, which is an organic reagent that is used as an indicator in cobalt titration. It turns red when it forms a complex with metal ions such as Co2+.
Some other examples include eriochrome black T(for aluminum, cadmium, zinc, calcium, and magnesium), hematoxylin (for copper), murexide (calcium ions) and calcein (for calcium).
What is the application of metal ion indicators?
- The major application of metal ion indicator is that it is used to precisely determine the endpoint of a complexometric titration.
- In the pharmaceutical sector, it is commonly used to determine the metal concentration of a drug product.
- It is also utilized in the process of determining the total hardness present in water.
Is eriochrome black T a metal ion indicator?
Yes, EBT is a metal ion indicator for complexometric titrations. It forms a colored complex with calcium (Ca), magnesium (Mg), and other metal ions when it is protonated.
What is the role of metal ion indicators in complexometric titration?
In complexometric titrations, commonly used indicators are the organic dyes. These dyes do their work by forming a colored complex with the metal ion that is being titrated. During the reaction, EDTA replaces the indicator to form a more stable complex with the metal. When the reaction happens, the color changes.
How do you identify colored metal ions?
In chemistry, an analytical procedure known as the flame test is used to detect the presence of certain elements, most prominently metal ions, based on properties characteristic to each element.
What color are metal ions?
The following lists the colors of common transition metal ions in an aqueous solution.
|
Transition
Metal Ion |
Colour |
|
Ferrous
ion Iron (Fe2+) |
Olive green |
|
Cobalt (Co2+) |
Pink |
|
Ferric
ion (Fe3+) |
Yellow |
|
Manganese
Mn2+ |
Pale Pink |
|
Dichromate
(Cr2O72-) |
Yellow |
|
Chromium
(Cr2+) |
Blue-violet |
|
Titanium
(Ti3+) |
Purple |
|
Titanium (Ti2+) |
Pale brown |
|
Zinc
(Zn2+) |
Colorless |
|
Vanadium
(V4+) |
Blue-grey |
Keywords:
EDTA titration curve, metallochromic indicators, ph of buffer solution, types of metal ion indicator, hardness of water, electrode, selectivity, almagite, PAN, masking and damasking agents.
References:
- ‘Complexation Titration’. Chemistry LibreTexts, 23 Nov. 2014, Available Here:
- ‘Complexometric Indicator’. Wikipedia, 12 Aug. 2022. Wikipedia, Available Here:
- ‘Colours of Transition Metal Ions’. Unacademy, Available Here:
- Rattenbury em. Complexometric titrations. In: introductory titrimetric and gravimetric analysis. Elsevier; 1966:130-139.
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