Ch 20 Applications of Oxidation/Reduction Titrations Flashcards
The analyte in an oxidation/reduction titration must be in a single oxidation state at the outset. Often, however, the steps that precede the titration, such as dissolving the sample and separating interferences, convert the analyte to a mixture of oxidation states. Therefore, we need
Auxiliary Oxidizing
and Reducing Reagents
The analyte solution must be
filtered to remove granular or powdered forms of the metal. An alternative to filtration
is the use of a
reductor
reductor that has a diameter of about 2 cm and holds a 40- to 50-cm column of amalgamated zinc
Jones reductor
reductor where a granular metallic silver held in a narrow glass column is the reductant, sometimes carried out from hydrochloric acid solutions of the analyte
walden reductor
What are some Auxiliary Oxidizing Reagents
Sodium Bismuthate
Ammonium Peroxydisulfate
Sodium Peroxide and Hydrogen Peroxide
is a sparingly soluble solid and a powerful oxidizing agent capable, for example, of converting manganese(II) quantitatively to permanganate ion.
Sodium bismuthate (NaBiO3)
is also a powerful oxidizing agent that uses traces of silver ion as catalyst. In acidic solution, it converts chromium(III) to dichromate, cerium(III) to cerium(IV),
and manganese(II) to permanganate.
Ammonium peroxydisulfate, [(NH4)2S2O8]
is a convenient oxidizing agent either as the solid sodium salt or as a dilute solution of the acid
Sodium Peroxide and Hydrogen Peroxide
direct titration of oxidizing analytes using reductants namely;
Iron(II) Solutions
Sodium Thiosulfate
is a moderately strong reducing agent that has been widely
used to determine oxidizing agents by an indirect procedure in which iodine is an
intermediate
Thiosulfate ion (S2O3^-2)
Common Oxidants Used as Standard Solutions
Potassium permanganate
Potassium bromate
Cerium (IV)
Potassium dichromate
Iodine
Strong Oxidants Used as Standard Solutions
Potassium Permanganate and Cerium(IV)
Potassium Permanganate vs. Cerium(IV) - more advantageous?
Cerium(IV)
Potassium Permanganate vs. Cerium(IV) - often used?
Potassium Permanganate - due to its intense color that serve as an indicator in titrations
widely used primary standard in Standardizing Permanganate and Ce(IV) Solutions
Sodium oxalate
is a type of catalysis
in which the product of a reaction
catalyses the reaction. This phenomenon causes the rate of the reaction to
increase as the reaction proceeds.
Autocatalysis
An oxidant that is indefinitely stable, can be boiled without decomposition, and does not react with hydrochloric acid. It has a lower electrode potential than Potassium Permanganate and Cerium(IV).
Potassium dichromate
is a weak oxidizing agent used primarily for the determination of strong reductants. Though it has a smaller electrode potential, it imparts a degree of selectivity that makes possible the determination of strong
reducing agents in the presence of weak ones.
Iodine solution
An oxidant that is a source of Bromine
Potassium Bromate
An oxidant that is used to determination 8-hydroxyquinoline and estimate the olefinic unsaturation in fats, oils, and petroleum products.
bromine
is based on the oxidation of sulfur dioxide by iodine. In a
solvent that is neither acidic nor basic—an aprotic solvent
Karl Fischer reaction
An end point in a Karl Fischer titration can be observed visually based on the _________ of the excess reagent
brown
color
Is based on the oxidation of sulfur dioxide by iodine
Karl fischer reaction
Detecting the endpoint of the carl fisher titration can be observed visually based on
Brown color of the excess reagent
