Permanganate ion reduction

Bromide ndIodide. The spectrophotometric determination of trace bromide concentration is based on the bromide catalysis of iodine oxidation to iodate by permanganate in acidic solution. Iodide can also be measured spectrophotometricaHy by selective oxidation to iodine by potassium peroxymonosulfate (KHSO ). The iodine reacts with colorless leucocrystal violet to produce the highly colored leucocrystal violet dye. Greater than 200 mg/L of chloride interferes with the color development. Trace concentrations of iodide are determined by its abiUty to cataly2e ceric ion reduction by arsenous acid. The reduction reaction is stopped at a specific time by the addition of ferrous ammonium sulfate. The ferrous ion is oxidi2ed to ferric ion, which then reacts with thiocyanate to produce a deep red complex. 

Sometimes, though, it is by no means obvious how a given half-equation is to be balanced. This commonly happens when elements other than those being oxidized or reduced take part in the reaction. Most often, these elements are oxygen (oxid. no. = — 2) and hydrogen (oxid. no. = +1). Consider, for example, the half-equation for the reduction of the permanganate ion,... 

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 ... 

This enables us to calculate the effect of change in the ratio [Mn04 ]/[Mn2 + ] at any hydrogen ion concentration, other factors being maintained constant. In this system, however, difficulties are experienced in the calculation owing to the fact that the reduction products of the permanganate ion vary at different hydrogen ion concentrations. In other cases no such difficulties arise, and the calculation may be employed with confidence. Thus in the reaction ... 

Write a balanced half-reaction that shows the reduction of permanganate ions, Mn04, to manganese(II) ions in an acidic solution. 

Ceric ammonium nitrate is used as a volumetric oxidizing reagent in many oxidation-reduction titrations. Cerium(IV) ion is a strong oxidant simdar to permanganate ion. It is the most widely-used primary standard among all Ce(IV) compounds. Other apphcations of this compound are in organic oxidation reactions and as a catalyst in polymerization of olefins. 

How does the medium affect the nature of reduction of the permanganate in an aqueous solution Compare the values of the standard electrode potentials of the permanganate ion in an acid and neutral media (see Appendix 1, Table 21). 

Perhaps even more important is the effect of hydrogen ion concentration on the emf of a half-reaction of a particular species. Consider the permanganate ion as an oxidizing agent in acid solution (as it often is). From the Latimer diagram above we can readily see that the reduction emf is 1.51 V when all species have unit activity. What is not shown is the complete equation ... 

Magnesium metal burns in air with an intense white light to form solid magnesium oxide. Red phosphorus reacts with liquid bromine to form liquid phosphorus tribromide. Purple aqueous permanganate ion, MnC>4-, reacts with aqueous Fe2+ ion to yield Fe3+ and pale pink Mn2+. Although these and many thousands of other reactions appear unrelated, all are oxidation-reduction reactions. 

Addition of aqueous Br to a solution of Mn04 causes a reduction of the permanganate ion, discharging the intense purple color. 

Reduction is defined as the gain of electrons. The conversion of Ag1+ —> Ag° involves a gain of an electron by file silver ion and thus silver is reduced. Likewise, file permanganate ion Mn( )4 has MnfVII] but MnC>2 manganese dioxide has Mn[IV]. Thus file gain of three electrons by manganese causes a reduction in oxidation level of from +7 to +4. 

Similarly, from the Tables 1.17 and 1.18 we can see, for example, that permanganate ions (in acid medium) can oxidize chloride, bromide, iodide, iron(II), and hexacyanoferrate(II) ions, also that iron(III) ions may oxidize arsenite or iodide ions but never chromium(III) or chloride ions etc. It must be emphasized that the standard potentials are to be used only as a rough guide the direction of a reaction will depend on the actual values of oxidation-reduction potentials. These, if the concentrations of the species are known, can be calculated easily by means of the Nernst equation. 

On reduction in acidic solution the permanganate ion accepts five electrons, to form the manganous ion ... 

What reduction product is formed ivhen dichiornate ion is reduced in acidic solution When permanganate ion is reduced in acidic solution When permanganate ion is reduced in basic solution Write the electron reactions for these three cases. 

Reducing agents cause reduction to happen and are themselves oxidized. The iron(II) ion caused the reduction of the permanganate ion and was the reducing agent. Common ones are metals, hydrogen, and carbon. 

An aqueous solution of potassium permanganate (KMn04) appears deep purple. In aqueous acidic solution, the permanganate ion can be reduced to the pale-pink manganese(II) ion (Mn ). Under standard conditions, the reduction potential of an MnOijlMn half-cell is = 1.49 V. Suppose this half-cell is combined with a Zn Zn half-cell in a galvanic cell, with [Zn ] = [MnO ] = [Mn ] = [H3O ] = 1 M. (a) Write equations for the reactions at the anode and the cathode, (b) Write a balanced equation for the overall cell reaction, (c) Calculate the standard cell potential difference, A%°. 

For an electrode containing a conventional oxidation-reduction system, terms are included in both numerator and denominator of equation (45.15). For example, if the system is manganous-permanganate ions, as ven in 45a, the expression for the electrode potential is... 

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