Iodine standard reduction potentials

Use standard reduction potentials to show why sulfuric acid could not be used to oxidize fluorides to fluorine but was used by Courtois to produce iodine from iodides. Why did Courtois have to use concentrated sulfuric acid ... 

The direct iodometric titration method (sometimes termed iodimetry) refers to titrations with a standard solution of iodine. The indirect iodometric titration method (sometimes termed iodometry) deals with the titration of iodine liberated in chemical reactions. The normal reduction potential of the reversible system ... 

In this equation sJ> j2, j- represents the standard oxidation potential of the iodine electrode (sJ.tija j- — — 0.535 V) and aj- the activity of iodide ions in the solution. The negative value of this potential means that in combination with a hydrogen electrode a spontaneous reduction process will take place at the iodine electrode during which iodine will pass into the solution in ionic form. 

Before surgical procedures are performed, it is standard that the proposed operative site be prepared with an effective antimicrobial to reduce the microbial populations residing on the skin and, thereby, the potential for surgery-associated infection. Povidone iodine and chlorhexidine gluconate (CHG) have been the two most prevalent antimicrobial choices for preoperative patient skin preparation over the years. In efficacy trials using human volunteers whose baseline counts exceed 10 microorganisms/cm on moist skin sites, both antimicrobial products commonly demonstrate at least a 3 logio reduction in resident skin flora within 10 minutes of skin preparation [1]. When a formulation contains at least 60% alcohol, these reductions are observed within seconds. 

The standard iodometric method for peroxide value requires a sample of 5 g for peroxide values below 10, and about 1 g for higher peroxide values. The sensitivity of this method is about 0.5 meq/kg, and can be improved by determining the iodine starch-end point colorimetrically, or the liberated iodine electrometrically by reduction at a platinum electrode maintained at constant potential. 

We notice that it is not necessary to achieve the reaction in neutral or weakly alkaline medium as with iodine for arsenious acid to be sufficiently reductant. We also notice that arsenious acid is oxidized before chloride ions. This is normal because of the standard potential values of the different couples brought together. 

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