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Permanganometry
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<h2 id="reaction">Reaction</h2> <p>Depending on the conditions in which the titration is performed, the manganese is reduced from an oxidation of +7 to +2, +4, or +6. </p><p>In most cases, permanganometry is performed in a very acidic solution in which the following <a href="/facts/Electrochemical/C0RUWpBH">electrochemical</a> reaction occurs:<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p> MnO−4 + 8 H+ + 5 e− → Mn2+ + 4 H2O; <i>E</i>° = +1.51 V<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> <p>which shows that KMnO4 (in an acidic medium) is a very strong oxidizing agent, able to oxidize <a href="/facts/Iron/QK1JYy8E">Fe</a>2+ (<i>E</i>°Fe3+/Fe2+ = +0.77 V), <a href="/facts/Tin/obW9mqc3">Sn</a>2+ (<i>E</i>°Sn4+/Sn2+ = +0.2 V), and even <a href="/facts/Chlorine/y27UwYBM">Cl</a>− (<i>E</i>°Cl2/Cl− = +1.36 V). </p><p>In weak acidic medium MnO−4 can not accept 5 electrons to form Mn2+. Instead, it accepts only 3 electrons and forms solid <a href="/facts/Manganese_dioxide/HRwgXlUe">MnO2</a> by the following reaction: </p> MnO−4 + 4 H+ + 3 e− → MnO2 + 2 H2O; <i>E</i>° = +1.69 V <p>In a strongly <a href="/facts/Base_(chemistry)/M9wA7qeM">basic</a> solution, with the <a href="/facts/Concentration/wqBmz5od">concentration</a> c(NaOH) >1 mol dm−3, only one electron is accepted to produce <a href="/facts/Manganate/3Kr1qk0S">manganate</a>: </p> MnO−4 + e− → MnO2−4; <i>E</i>° = +0.56 V<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Redox titrations: Permanganometry. In: University Chemistry, Vol. 1. C. Parameshwara Murthy. New Age International, 2008. ISBN 81-224-0742-0. p.632 <a href="https://books.google.com/books?id=0xl17YU8WzQC&pg=PA632" target="_blank">https://books.google.com/books?id=0xl17YU8WzQC&pg=PA632</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Louis Rosenfeld. Four Centuries of Clinical Chemistry. CRC Press, 1999, p. 130-175. <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Kolthoff, Izaak Maurits (1929). Volumetric Analysis. J. Wiley & Sons, Incorporated. <a href="https://books.google.com/books?id=XQIIAQAAIAAJ" target="_blank">https://books.google.com/books?id=XQIIAQAAIAAJ</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Table of standard reduction potentials. In: Chemistry and chemical reactivity. John C. Kotz, Paul Treichel, John R. Townsend. Cengage Learning, 2008. ISBN 0-495-38703-7. p. 920 <a href="https://books.google.com/books?id=jcn6sgt7RpoC&pg=PA920" target="_blank">https://books.google.com/books?id=jcn6sgt7RpoC&pg=PA920</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Louis Rosenfeld. Four Centuries of Clinical Chemistry. CRC Press, 1999, p. 72-75. <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> </ol>