Ferrous/ferric ions

Let us consider an electronic transfer reaction of the redox couple of ferrous-ferric ions ... 

The ferrous-ferric ion analytical technique was used to determine the ozone concentration of the stock solution. Enough ferrous ammonium sulfate was added to an aliquot of ozone to bring 100 ml. of the solution to about 0.005iV and the nonoxidized ferrous ions were then back-titrated with 0.1 A potassium permanganate. The chlorine concentration was determined iodometrically (2). 

Redox status (largely controlled by oxygen level, ferrous/ferric ion ratio)... 

However, although the Haber-Willstatter chain reactions have been assumed to occur in certain catalytic systems, notably the ferrous-ferric ion system (4), more recent evidence to be described subsequently, does not support this assumption. On the other hand, such reactions appear to offer the most plausible explanation for the photochemical decomposition of hydrogen peroxide, although even here a satisfactory analysis of the kinetics has yet to be made. 

Hydrogen peroxide is inherently very stable but the presence of minute amounts (less than ppm) of some catalytic impurities (ferrous/ferric ions, cuprous and cupric ions) can give rise to quite high rates of decomposition. The pH of the solution can affect both the solubility of a catalytic ion as well as its activity as a decomposition agent. 

Noufi, Frank and co-workers have reported that the photocorrosion of single crystal n-gallium arsenide and polycrystalline n-silicon electrodes can be suppressed when used in aqueous solutions containing ferrous/ferric ions. The coated n-silicon electrode had a short circuit current of 2.9 mA/cm, a power efficiency of 3 %, and functioned for 122 hours of continuous irradiation (143 mW/cm ) with only a 30 % reduction in the photocurrent. For comparison, the current decays to zero within a minute with a uncoated electrode . These results are shown in Fig. 10. The n-gallium arsenide electrode showed a similar photocurrent response. Adhesion of the film to the semiconductor surface is a problem with these electrodes and is much more prevalent with the gallium arsenide, where the film peels off the electrode in aqueous solutions. 

Mizutani, N. Iwasaki, T. Watano, S. Yanagida, T. Tanaka, H. Kawai, T. (2008). Effect of the ferrous/ ferric ions molar ratio on the reaction mechanism for the hydrothermal synthesis of magnetite nanop)articles. Bull. Mater. Set, 31, 713-717. 

Upon boiling the alkaline ferrous salt solution, some ferric ions are inevitably produced by the action of the air upon the addition of dilute siilphurio acid, thus dissolving the ferrous and ferric hydroxides, the ferrocyanides reacts with the ferric salt producing ferric ferrocyanide (Prussian blue) ... 

The mechanism and rate of hydrogen peroxide decomposition depend on many factors, including temperature, pH, presence or absence of a catalyst (7—10), such as metal ions, oxides, and hydroxides etc. Some common metal ions that actively support homogeneous catalysis of the decomposition include ferrous, ferric, cuprous, cupric, chromate, dichromate, molybdate, tungstate, and vanadate. For combinations, such as iron and... 

Historically, ferrous sulfamate, Fe(NH2S02)2, was added to the HNO scmbbing solution in sufficient excess to ensure the destmction of nitrite ions and the resulting reduction of the Pu to the less extractable Pu . However, the sulfate ion is undesirable because sulfate complexes with the plutonium to compHcate the subsequent plutonium purification step, adds to corrosion problems, and as SO2 is an off-gas pollutant during any subsequent high temperature waste solidification operations. The associated ferric ion contributes significantly to the solidified waste volume. 

The hberated iodine, as the complex triiodide ion, may be titrated with standard thiosulfate solution. A general iodometric assay method for organic peroxides has been pubUshed (253). Some peroxyesters may be determined by ferric ion-catalyzed iodometric analysis or by cupric ion catalysis. The latter has become an ASTM Standard procedure (254). Other reducing agents are ferrous, titanous, chromous, staimous, and arsenite ions triphenylphosphine diphenyl sulfide and triphenjiarsine (255,256). 

ThioglycoHc acid can be identified by its in spectmm or by gas chromatography. Most of the by-products and self-esterification products are also detected by liquid chromatography, eg, thiodiglycolic acid, dithiodiglycolic acid, linear dimers, and polymers. Iron content can be assayed by the red sensitive complex of 1,10-phenanthroline [66-71-7] and ferrous ion of a mineralised sample. Ferric ion turns an aqueous ammonia solution deep red-violet. 

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. 

The ease with which the ferrous ion can be oxidized to a ferric ion in the electrowinning cell furthers this reaction. Attack on the copper is most apparent at the solution line, where it results in corrosion of the loops supporting the cathodes, leading to dropped cathodes. 

During acid cleaning or severe acid upsets, ferric-ion concentration may increase, albeit much more slowly than ferrous-ion concentration, to high levels. Resulting corrosion can be severe. Iron is oxidized, and... 

The yield of 3-hydroxyquinoline relative to the amount of quinoline consumed is low but is increased markedly by the presence of ascorbic acid. This was attributed to the regeneration of ferrous ions by reduction of the ferric ion formed in the first step of the reaction. 

Although a good inhibitor reduces the acid attack, it does not prevent the attack of oxidising agents on the exposed base metal. Thus the ferric ions resulting from the gradual dissolution of the detached magnetite and haematite attack the exposed steel even in the presence of an inhibitor, and are reduced to ferrous ions. 

The reaction between ferric ion, Fe+3, and cuprous ion, Cu+, to produce ferrous ion, Fe+2, and cupric ion, Cu+2, is plainly an oxidation-reduction reaction ... 

Use oxidation numbers to balance the reaction between ferrous ion, Fe+2, and permanganate ion, MnOr, in acid solution to produce ferric ion, Fe+3, and manganous ion, Mn+2. 

Ferrous ion, iron(II), forms a complex with six cyanide ions, CN- the octahedral complex is called ferrocyanide. Ferric ion, iron(III), forms a complex with six cyanide ions the octahedral complex is called ferricyanide. Write the structural formulas for the ferrocyanide and the ferricyanide complex ions. 

NOTE It is also apparent that the ferric ion (Fe3+) should chelate most readily. In practice, however, under strongly alkaline conditions, the preferred reaction is to instantaneously form ferrous hydroxide and then to slowly revert to ferric hydroxide (competing anion effect). 

Hydrochloric acid/stannous chloride. Modifications of the standard HC1 cleaning program to aid control corrosion of exposed steel include the addition of HF, as discussed earlier, but also stannous chloride. Where the cleaning program is likely to remove considerable volumes of rust and magnetite, even in the presence of a nitrogen- and sulfur-based proprietary corrosion inhibitor, rapid corrosion of exposed steel may develop. This is because the ferric ions (Fe3+) released from ferric oxide act to reduce the exposed steel to ferrous ions (Fe2+). 

If stannous chloride (SnCl2 2H20) is added, it preferentially reduces the ferric ion to ferrous ion. Two pounds of stannous chloride will reduce 1 pound of ferric ion ... 

Some older systems of nomenclature are still in use. For example, some cations were once denoted by the endings -ous and -ic for the ions with lower and higher charges, respectively. To make matters worse, these endings were in some cases added to the Latin form of the element s name. Thus, iron(II) ions were called ferrous ions and iron(III) ions were called ferric ions (see Appendix 3C). We do not use this system in this text, but you will sometimes come across it and should be aware of it. 

The earliest attempts to measure the rate of exchange between ferrous and ferric ions in aqueous media utilised the diffusion separation technique. Little agreement was obtained by the different workers Diffusion separation factors, found to be 0.5 , 1.4, 3.5 and 1.2, illustrate the difficulty of the technique. The isotopes used to label the iron were either Fe or Fe, and exchange was found to be complete in hours or many days > in perchlorate media. 

Silverman and Dodson made the first detailed isotopic study of this exchange system using the separation afforded by the addition of 2,2 -dipyridyl at pH 5, followed by the precipitation of the ferric iron with either ammonia or 8-hydro-xyquinoline. Dodson , using this separation method, had previously obtained an overall rate coefficient of 16 l.mole" sec at 23 °C for 0.4 M perchloric acid media. The exchange in perchlorate and perchlorate-chloride media was found to conform to a rate law, first order with respect to both total ferrous and ferric ion concentrations, with an observed rate constant (k bs) dependent on the hydrogen-ion concentration, viz. 

The method is based on the oxidation of ferrous ions to ferric ions, which form a deep red complex with thiocyanate. 

Scale prevention methods include operating at low conversion and chemical pretreatment. Acid injection to convert COs to CO2 is commonly used, but cellulosic membranes require operation at pH 4 to 7 to prevent hydrolysis. Sulfuric acid is commonly used at a dosing of 0.24 mg/L while hydrochloric acid is to be avoided to minimize corrosion. Acid addition will precipitate aluminum hydroxide. Water softening upstream of the RO By using lime and sodium zeolites will precipitate calcium and magnesium hydroxides and entrap some silica. Antisealant compounds such as sodium hexametaphosphate, EDTA, and polymers are also commonly added to encapsulate potential precipitants. Oxidant addition precipitates metal oxides for particle removal (converting soluble ferrous Fe ions to insoluble ferric Fe ions). 

---