Redox titration
Encyclopedia
Redox titration is a type of titration
based on a redox reaction between the analyte
and titrant.
Redox titration may involve the use of a redox indicator
and/or a potentiometer
.
with a reducing agent and using starch
as indicator. Iodine forms an intensely blue complex
with starch. Iodine (I2) can be reduced to iodide
(I−) by e.g. thiosulphate (S2O32−), and when all iodine is spent the blue colour disappears. This is called an iodometric
titration.
Most often the reduction of iodine to iodide is the last step in a series of reactions where the initial reactions are used to convert an unknown amount of the solute
(the substance you want to analyze) to an equivalent amount of iodine, which may then be titrated. Sometimes other halogen
s than iodine are used in the intermediate reactions because they are available in better measurable standard solution
s and/or react more readily with the solute. The extra steps in iodometric titration may be worth while because the equivalence point
, where the blue turns colourless, is more distinct than some other analytical methods.
Titration
Titration, also known as titrimetry, is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of an identified analyte. Because volume measurements play a key role in titration, it is also known as volumetric analysis. A reagent, called the...
based on a redox reaction between the analyte
Analyte
An analyte, or component , is a substance or chemical constituent that is of interest in an analytical procedure. Grammatically, it is important to note that experiments always seek to measure properties of analytes—and that analytes themselves can never be measured. For instance, one cannot...
and titrant.
Redox titration may involve the use of a redox indicator
Redox indicator
A redox indicator is an indicator that undergoes a definite color change at a specific electrode potential....
and/or a potentiometer
Potentiometer (measuring instrument)
A potentiometer is an instrument for measuring the potential in a circuit. Before the introduction of the moving coil and digital volt meters, potentiometers were used in measuring voltage, hence the '-meter' part of their name...
.
Example
An example of a redox titration is treating a solution of iodineIodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
with a reducing agent and using starch
Starch
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...
as indicator. Iodine forms an intensely blue 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 starch. Iodine (I2) can be reduced to iodide
Iodide
An iodide ion is the ion I−. Compounds with iodine in formal oxidation state −1 are called iodides. This page is for the iodide ion and its salts. For information on organoiodides, see organohalides. In everyday life, iodide is most commonly encountered as a component of iodized salt,...
(I−) by e.g. thiosulphate (S2O32−), and when all iodine is spent the blue colour disappears. This is called an iodometric
Iodometry
Iodometry, also known as iodometric titration, is a method of volumetric chemical analysis, a redox titration where the appearance or disappearance of elementary iodine indicates the end point....
titration.
Most often the reduction of iodine to iodide is the last step in a series of reactions where the initial reactions are used to convert an unknown amount of the solute
Solute
Solute may refer to:* Solute, UMIK or UBOOK desolving in a substance,forming INT/INTY* Solute , a group of Paleozoic echinoderms...
(the substance you want to analyze) to an equivalent amount of iodine, which may then be titrated. Sometimes other halogen
Halogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...
s than iodine are used in the intermediate reactions because they are available in better measurable standard solution
Standard solution
In analytical chemistry, a standard solution is a solution containing a precisely known concentration of an element or a substance i.e, a known weight of solute is dissolved to make a specific volume. It is prepared using a standard substance, such as a primary standard. Standard solutions are used...
s and/or react more readily with the solute. The extra steps in iodometric titration may be worth while because the equivalence point
Equivalence point
The equivalence point, or stoichiometric point, of a chemical reaction when a titrant is added and is stoichiometrically equal to the amount of moles of substance present in the sample: the smallest amount of titrant that is sufficient to fully neutralize or react with the analyte...
, where the blue turns colourless, is more distinct than some other analytical methods.
See also
- TitrationTitrationTitration, also known as titrimetry, is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of an identified analyte. Because volume measurements play a key role in titration, it is also known as volumetric analysis. A reagent, called the...
- Oxidizing agentOxidizing agentAn oxidizing agent can be defined as a substance that removes electrons from another reactant in a redox chemical reaction...
- Reducing agentReducing agentA reducing agent is the element or compound in a reduction-oxidation reaction that donates an electron to another species; however, since the reducer loses an electron we say it is "oxidized"...
- Redox indicatorRedox indicatorA redox indicator is an indicator that undergoes a definite color change at a specific electrode potential....
- IodometryIodometryIodometry, also known as iodometric titration, is a method of volumetric chemical analysis, a redox titration where the appearance or disappearance of elementary iodine indicates the end point....
- CerimetryCerimetryCerimetry or cerimetric titration, also known as cerate oximetry, is a method of volumetric chemical analysis, a redox titration in which a Fe2+-1,10-phenanthroline complex color change indicates the end point. Ferroin can be reversibly discolored in its oxidized form upon titration with a Ce4+...