Redox titration permanganate

The concentration of Fe2+ ions in an acid solution can be determined by a redox titration with either KM11O4 or K2Cr207. The reduction products of these reactions are Mir4 and Cr5+, respectively, and in each case the iron is oxidized to Fe3+. In one titration of an acidified Fe2 solution, 25.20 mL of 0.0210 m K2Cr207(aq) was required for complete reaction. If the titration had been carried out with 0.0420 M KMn()4(aq), what volume of the permanganate solution would have been required for complete reaction ... 

The concept of reduction potential is introduced in Chapter 6. When the reduction potentials of two species differ by 0.1 V or more, the resulting redox reaction will proceed rapidly and stoichiometrically so that it may be used as the basis for a titrimetric procedure. The end point of a redox titration may be observed by following the potential of the titrand with an indicator electrode or with a visual indicator. In two special cases, the reagent (potassium permanganate and iodine) is self-indicating (vide infra). 

Redox titration using potassium permanganate as the oxidising reagent and self-indicator. 

Potassium ozonide, 735 Potassium permanganate chemiluminescence, 643 hydrogen peroxide titration, 627 ozonide redox titration, 736 Potassium peroxymonosulfate, dioxirane preparation, 26, 1020-30, 1130 Potassium superoxide, commercial availability, 620... 

Redox titration is used in pharmacopoeia assays of ferrous salts, hydrogen peroxide, sodium perborate and benzoyl peroxide by titration with KMn04. In the case of KMn04 titrations the end-point may be detected when the purple colour of the permanganate persists. 

Although coordination compounds have sometimes been used as titrants, e.g. ferrocyanide ions for the titration of zinc(II), and permanganate or dichromate ions in redox titrations, probably the only outstanding reaction in classical titrimetry that involves the reversible formation of a coordination compound is the Liebig-Deniges reaction. 

The neutralisation of acids with bases provides many valuable volumetric methods of chemical analysis and redox titrations are useful as well. But here we encounter an important difference between acid/base and redox reactions in solution. Acid/base reactions which involve the transfer of protons are very fast indeed they are usually instantaneous for all practical purposes. In protonic solvents, polar H-X bonds are very labile and undergo rapid proton exchange. For example, if B(OH)3 - a very weak acid - is recrystallised from D20, we obtain a fully-deuterated product. Redox reactions, on the other hand, are often very slow under ordinary conditions. To return to the analogy between acid/base and redox titrations, many readers will be familiar with the reaction between permanganate and oxalic acid the reaction is very slow at room temperature and, for titrimetric purposes, should be carried out at about 60 °C. The mechanism whereby a redox reaction takes place tends to be... 

Unfortunately, potassium permanganate is not obtainable in high enough purity and can undergo decomposition by exposure to sunlight. Therefore it cannot be used as a primary standard (p. 143). However, it can be used in redox titrations provided it is standardized with sodium oxalate (which is available in high purity). The redox reaction involving oxalate is as follows ... 

Redox titrations are illustrated by the reaction in which potassium permanganate oxidizes Fe in acidic solution and the manganese (Mn) is reduced ... 

The redox titration is carried out using permanganate and oxalic acid. First, a known excess amount of KMnO is added into the sample HCOOH solution, which is adjusted to alkaline pH using Na,CO. prior to the addition of permanganate warm the solution to facilitate the redox reaction then add a known excess amount of oxalic acid solution and a small amount of H,SO, to the mixture to dissolve the precipitated MnO. Excess oxalic acid is back titrated with KMnO. A blank titration should be conducted to determine the background values of the reagents and the water used. 

If we want to determine hydrogen peroxide concentration, this reaction can be carried out as a redox titration, using a standard permanganate solution. 

The only common redox titration applied in the clinical laboratory is for the analysis of calcium in biological fluids. Calcium oxalate is precipitated and filtered, the precipitate is dissolved in acid, and the oxalate, which is equivalent to the calcium present, is titrated with standard potassium permanganate solution. This method is largely replaced now by more convenient techniques such as complex-ometric titration with EDTA (Chapter 9) or measurement by atomic absorption spectrophotometry (Chapter 17). 

EXPERIMENT 18 MICROSCALE QUANTITATIVE ANALYSIS OF HARD-WATER SAMPLES USING AN INDIRECT POTASSIUM PERMANGANATE REDOX TITRATION ... 

Total uranium can be analyzed by redox titration against acidified potassium permanganate, ceri-um(IV), or potassium dichromate. Uranium is reduced prior to the titration with zinc amalgam. Dichromate titrations are used to determine uranium concentrations in dissolved uranium metal, uranium ore, or yellow cake (UO3) samples. There are potential interferences from bismuth, manganese, platinum, silver, vanadium, and zirconium, which must therefore be removed prior to the titration. 

Explain why potassium permanganate (KMn04) and potassium dichromate (K2Cr207) can serve as internal indicators in redox titrations. 

In analytical chemistry, a redox titration is based on an oxidation-reduction reaction between analyte and titrant. Common analytical oxidants include iodine (I2), permanganate (MnOJ), cerium(IV), and dichromate (Cr207 ). Titrations with reducing agents such as Fe " (ferrous ion) and Sn " (stannous ion) are less common because solutions of most reducing agents need protection from air to prevent reaction with O2. 

Problem Permanganate ion is a strong oxidizing agent, and its deep purple color makes it useful as an indicator in redox titrations. It reacts in basic solution with the oxalate ion to form carbonate ion and solid manganese dioxide. Balance the skeleton ionic equation for the reaction between NaMn04 and Na2C204 in basic solution ... 

Figure 12.20 A typical redox titration curve for hydrogen peroxide measurement. The left ordinate is the millivolt reading from the redox electrode the right ordinate is the first derivative of the millivolt curve. Volume (mL) of titrant (permanganate) is shown on the abscissa. The endpoint shown is calculated with the first derivative method—the maximum of the pink curve. Used with permission from the author.

In the following chapter, we shall see an example of the use ofEq. (16.11) when we study the redox titration curve of hypovanadous ions V + by permanganate ions Mn04 . 

An example of a redox titration in which a simultaneous exchange of electrons and protons occurs is provided by the titration of the ferrous ion by the permanganate ion according to the reaction... 

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