Complexometric indicator
Encyclopedia
A complexometric indicator is an ionochromic
dye
that undergoes a definite color change in presence of specific metal ion
s. It forms a weak complex
with the ions present in the solution, which has a significantly different color from the form existing outside the complex.
Complexometric indicators are also known as pM indicators.
, complexometric indicator
s are used in complexometric titration
to indicate the exact moment when all the metal ions in the solution are sequestered by a chelating agent (most usually EDTA
). Such indicators are also called metallochromic indicators.
The indicator may be present in another liquid phase in equilibrium with the titrated phase, the indicator is described as extraction indicator.
Some complexometric indicators are sensitive to air and are destroyed. When such solution loses color during titration, a drop or two of fresh indicator may have to be added.
can function as a complexometric indicator.
Ionochromism
Ionochromic materials, similar to photochromic, thermochromic and other chromic materials, alter colour in the presence of a factor and reverse to their initial state when the factor is removed. The factor which causes colour change in ionochromic substances are ions. A flow of ions through an...
dye
Dye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
that undergoes a definite color change in presence of specific metal ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s. It forms a weak complex
Complex (chemistry)
In chemistry, a coordination complex or metal complex, is an atom or ion , bonded to a surrounding array of molecules or anions, that are in turn known as ligands or complexing agents...
with the ions present in the solution, which has a significantly different color from the form existing outside the complex.
Complexometric indicators are also known as pM indicators.
Complexometric titration
In analytical chemistryAnalytical chemistry
Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials. Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of...
, complexometric indicator
Indicator
Indicator may mean:In chemistry:* pH indicator, a chemical detector for protons in acid-base titrations* Redox indicator, a chemical detector for redox titrations* Complexometric indicator, a chemical detector for metal ions in complexometric titrations...
s are used in complexometric titration
Complexometric titration
Complexometric titration is a form of volumetric analysis in which the formation of a colored complex is used to indicate the end point of a titration. Complexometric titrations are particularly useful for the determination of a mixture of different metal ions in solution...
to indicate the exact moment when all the metal ions in the solution are sequestered by a chelating agent (most usually EDTA
EDTA
Ethylenediaminetetraacetic acid, widely abbreviated as EDTA , is a polyamino carboxylic acid and a colourless, water-soluble solid. Its conjugate base is named ethylenediaminetetraacetate. It is widely used to dissolve limescale. Its usefulness arises because of its role as a hexadentate ligand...
). Such indicators are also called metallochromic indicators.
The indicator may be present in another liquid phase in equilibrium with the titrated phase, the indicator is described as extraction indicator.
Some complexometric indicators are sensitive to air and are destroyed. When such solution loses color during titration, a drop or two of fresh indicator may have to be added.
Examples
Complexometric indicators are water-soluble organic molecules. Some examples are:- Eriochrome Black TEriochrome Black TEriochrome Black T is a complexometric indicator that is part of the complexometric titrations, e.g. in the water hardness determination process. It is an azo dye.It is also known as ET-00....
for calciumCalciumCalcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
, magnesiumMagnesiumMagnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
and aluminiumAluminiumAluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances.... - Xylenol orangeXylenol orangeXylenol orange is an organic reagent, most commonly used as a tetrasodium salt as an indicator for metal titrations. When used for metal titrations it will appear red in the titrand and yellow once it reaches its endpoint...
for galliumGalliumGallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...
, indiumIndiumIndium is a chemical element with the symbol In and atomic number 49. This rare, very soft, malleable and easily fusible post-transition metal is chemically similar to gallium and thallium, and shows the intermediate properties between these two...
and scandiumScandiumScandium is a chemical element with symbol Sc and atomic number 21. A silvery-white metallic transition metal, it has historically been sometimes classified as a rare earth element, together with yttrium and the lanthanoids... - Methyl calcein blue
- MurexideMurexideMurexide , also called ammonium purpurate or MX, is the ammonium salt of purpuric acid. It may be prepared by heating alloxantin in ammonia gas to 100 °C, or by boiling uramil with mercury oxide. W.N...
- Fast Sulphon Black
- Eriochrome Red B
- CalceinCalceinCalcein, also known as fluorexon, fluorescein complex, is a fluorescent dye with an excitation and emission wavelengths of 495/515 nm, respectively. Calcein also self-quenches even at concentrations below 100mM. It is used as a complexometric indicator for titration of calcium ions with EDTA,...
- Calcon
- Eriochrome blue-black B
- Eriochrome blue SE
- Hydroxynaphthol blueHydroxynaphthol blueHydroxynaphthol blue is an azo dye. It is used for determining the endpoint in metal complexation titrations....
- Methylthymol blue
- Phthalein purple
- Pyrogallol red
- 3,3'-dimethylnaphthidine
- Chromazurol S
- Hematoxylin for copperCopperCopper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
- Naphthol green BNaphthol Green BNaphthol Green B is a green nitroso dye.-Chemistry:Naphthol Green B is the sodium salt of Naphthol Green Y . Its absorption maximum is 714 nm in water. It can be solved in water, however not in ethanol. As an anion, it acts as acid dye....
- 1-(2-pyridilazo)-2-naphthol (PAN)
- CalmagiteCalmagiteCalmagite is a complexometric indicator used in analytical chemistry to identify the presence of metal ions in solution. As with other metal ion indicators calmagite will change color when it is bound to an ion. Calmagite will be wine red when it is bound to a metal ion and may be blue, red, or...
- 2-Cresolphthalexon
Redox indicators
In some settings, when the titrated system is a redox system whose equilibrium is influenced by the removal of the metal ions, a redox indicatorRedox indicator
A redox indicator is an indicator that undergoes a definite color change at a specific electrode potential....
can function as a complexometric indicator.