A redox titration
is a type of
titration
Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte (a substance to be analyzed). A reagent, termed the ''titrant'' ...
based on a redox reaction between the
analyte
An analyte, component (in clinical chemistry), or chemical species is a substance or chemical constituent that is of interest in an analytical procedure. The purest substances are referred to as analytes, such as 24 karat gold, NaCl, water, etc. ...
and titrant. It may involve the use of a
redox indicator
A redox indicator (also called an oxidation-reduction indicator) is an indicator which undergoes a definite color change at a specific electrode potential.
The requirement for fast and reversible color change means that the oxidation-reduction e ...
and/or a potentiometer. A common example of a redox titration is treating a solution of
iodine
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
with a reducing agent to produce
iodide
An iodide ion is the ion Iā. Compounds with iodine in formal oxidation state ā1 are called iodides. In everyday life, iodide is most commonly encountered as a component of iodized salt, which many governments mandate. Worldwide, iodine defic ...
using a
starch indicator to help detect the endpoint.
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
(I
2) can be reduced to
iodide
An iodide ion is the ion Iā. Compounds with iodine in formal oxidation state ā1 are called iodides. In everyday life, iodide is most commonly encountered as a component of iodized salt, which many governments mandate. Worldwide, iodine defic ...
(I
−) by, say,
thiosulfate
Thiosulfate ( IUPAC-recommended spelling; sometimes thiosulphate in British English) is an oxyanion of sulfur with the chemical formula . Thiosulfate also refers to the compounds containing this anion, which are the salts of thiosulfuric acid, ...
(, and when all iodine is spent the blue colour disappears. This is called an
iodometric titration.
Most often of all, 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
In chemistry, a solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. If the attractive forces between the solvent ...
(the substance being analyzed) to an equivalent amount of iodine, which may then be titrated. Sometimes other
halogen
The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this group is ...
s (or haloalkanes) than iodine are used in the intermediate reactions because they are available in better measurable
standard solution In analytical chemistry, a standard solution is a solution containing a precisely known concentration of an element or a substance. A known mass of solute is dissolved to make a specific volume. It is prepared using a standard substance, such as a ...
s and/or react more readily with the solute. The extra steps in iodometric titration may be worthwhile because the
equivalence point
The equivalence point, or stoichiometric point, of a chemical reaction is the point at which chemically equivalent quantities of reactants have been mixed. For an acid-base reaction the equivalence point is where the moles of acid and the moles of ...
, where the blue turns a bit colourless, is more distinct than some other analytical or may be by volumetric methods.
The main redox titration types are:
:
Sources
:
See also
*
Oxidizing agent
An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or "Electron acceptor, accepts"/"receives" an electron from a (called the , , or ). In ot ...
*
Reducing agent
In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ).
Examples of substances that are commonly reducing agents include the Earth meta ...
{{DEFAULTSORT:Redox Titration
Titration