Permanganate reaction with oxalate

Extent of reaction can be ascertained by titrating the remaining oxalic acid with permanganate solution. For best results this... 

Sodium oxalate is a widely used primary standard. In acidic solutions, the oxalate ion is converted to the undissociated acid. Thus, its reaction with permanganate can be described by... 

The common treatment methods are acidification, neutralization, and incineration. When oxahc acid is heated slightly in sulfuric acid, it is converted to carbon monoxide, carbon dioxide, and water. Reaction with acid potassium permanganate converts it to carbon dioxide. Neutralization with alkahes, such as caustic soda, yields soluble oxalates. Neutralization with lime gives practically insoluble calcium oxalate, which can be safely disposed of, for instance, by incineration. 

In the laboratory you have observed the reaction of ferrous ion, Fe+i(aq), with permanganate ion, MnOiYaqJ, and also the reaction of oxalate ion, CiOi2(aq), with permanganate ion, MnO (aq). These studies show that the rate of a reaction depends upon the nature of the reacting substances. In Experiment 14, the reaction between IO and HSO3" shows that the rate of a reaction depends upon concentrations of reactants and on the temperature. Let us examine these factors one at a time. 

An example of catalytic action is provided by the titration of oxalates with potassium permanganate solution referred to above. It is found that even though the oxalate solution is heated, the first few drops of permanganate solution are only slowly decolorised, but as more permanganate solution is added the decoloration becomes instantaneous. This is because the reaction between oxalate ions and permanganate ions is catalysed by the Mn2+ ions formed by the reduction of permanganate ions ... 

The equivalence point occurs when the quantity of added titrant is the exact amount necessary for stoichiometric reaction with the analyte. For example, 5 mol of oxalic acid react with 2 mol of permanganate in hot acidic solution ... 

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... 

The violet complexes Mn(H2P 07)73 and Mn(C204)73 (both presumably chelates) are also known. The latter, when heated or illuminated strongly, undergoes an internal oxidation-reduction reaction, yielding C02 and an oxalate complex (or complexes) of Mn(II). The stability of the Mn(C204)73 complex at room temperature makes it necessary to carry out the familiar titration of oxalate with permanganate at elevated temperature (>60° 0). 

These direct titrations form the basis of more complicated analytical procedures. Many analytical procedures are indirect and involve additional preliminary reactions of the sample before the titration can be carried out. For example, a soluble calcium salt will not take part in a redox reaction with potassium permanganate. But adding ammonium oxalate to the solution containing Ca causes the quantitative precipitation of calcium oxalate ... 

Finally, the oxalic acid is titrated with permanganate solution of accurately known concentration, based on the redox reaction... 

Equivalent Weights in Oxidation/Reduction Reactions The equivalent weight of a participant in an oxidation/reduction reaction is that amount that directly or indirectly produces or consumes 1 mol of electrons. The numerical value for the equivalent weight is conveniently established by dividing the molar mass of the substance of interest by the change in oxidation number associated with its reaction. As an example, consider the oxidation of oxalate ion by permanganate ion ... 

Experiment 18.1 Temperature dependency of rate of reaction Potassium permanganate and acidulated oxalic acid solutions are brought to three different temperatures (in an ice bath at about 0 °C, at room temperature, and in a water bath of about 50 °C). Starting with the coldest oxalic acid solution, the potassium permanganate solution of the same temperature is added to each one. The hottest solution loses color by far the fastest. 

We use the term autocatalysis if a catalyst is formed only during the reaction. An example of this is the reaction of permanganate with oxalic acid,... 

A method, free from Fe or Cr interference, (MacDonald and Savage 1979) involves a prior oxidation of plutonium to Pu(VI) with an excess of Ce(IV). Sulfamic acid is added to avoid side reactions with nitrites. Fluoride residues from the dissolution of solid samples are complexed hy additon of Al(in). The excess Ce(IV) is then reduced by a slight excess of arsenite in the presence of Os(Vni) as catalyst. Excess As(III) is oxidized by permanganate, also in a very quantity. Finally, oxalic acid is added to reduce the excess Mn(VII). Pu(VI) is then reduced quantitatively to Pu(IV) with Fe(II) and the excess Fe(II) backtitrated with Cr(VI). All steps are followed potentiometrically and carefully timed. The Pu mass fraction, Cpu, in g/g, in the sample aliquant submitted to titration is calculated according to the following equation ... 

Here is one of the most complicated reactions. MnO (permanganate) reacts with (oxalate) in the presence of acid (H+) and the products are Mn, CO, (carbon dioxide), and H O (water). That is ... 

Precipitation techniques. Calcium can be precipitated as calcium oxalate and the oxalate can be measured by its reaction with potassium permanganate. 

Peroxysalts can be back-titrated with permanganate ions. This is the case of MnOa, PbOa, and Pb304. The peroxysalt is reduced in acidic medium. The reducing agent used is ferrous iron or oxalic acid, the excess of which is titrated with permanganate ions. Both redox reactions are (for example, with Mn02)... 

With regard to the determination of oxalic acid, see the standardization of potassium permanganate, above.) An interesting extension of the oxidization reaction of oxalic acid is the determination of calcium ions. The latter are precipitated as calcium oxalate in hot acetic acid (solubility product = 10 ). The precipitate is separated out from the solution, washed, and dissolved into a 2 mol/L sulfuric acid solution. After heating, the liberated oxalic acid is titrated with permanganate. In fact, oxalic acid is simply liberated by displacement of the precipitation equilibrium ... 

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