Sulfur Dioxide and Sulfite Ions

The reactions of SO2 with [Cr(NN)3] (NN = bpy, phen, and derivatives) when subjected to visible light (laser pulse) are threefold. Quenching yields [Cr(NN)3] which undergoes back electron transfer. The predominant reaction is electron transfer between SO2 and [Cr(NN)3] yielding the transient SO2. The rate constants obtained may be utilized in a Marcus cross-correlation relation to calculate a self-exchange rate of between 1 x 10 M s and 18 x 10 s for 

The kinetics of SO oxidation by [PtClg] have been studied over a wide range of experimental conditions.On the basis of the experimental evidence, a 2e reduction mechanism was proposed. The reduction of Cu(II) by SOl proceeds via Cu SOf and Cu2S030H intermediates. The rate law is consistent with consecutive first-order reactions leading to a mechanism involving complexation followed by a rate-determining electron transfer. Inner-sphere electron transfer is also assumed for the electron transfer between Fe(III) and The reduction 

The kinetics of the reduction of a series of Co(III), Fe(III), and Ru(III) complexes by dithionite have been investigated/ In most cases, the dominant reducing agent is the SOj radical which results from the dissociation of S2O4 . However, in two cases, rate constants for the reaction of undissociated 8204 species were obtained that are about 10 lower than those for reduction by SOJ. 

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It follows from these equilibria that the relative concentrations of sulfur dioxide, hydrogen sulfite, and sulfite are governed by the pH of the solution (Fig. 7-1). As can be seen, sulfur dioxide is present almost exclusively in the form of hydrogen sulfite ions at pH around 4. Below and above this value the concentrations of sulfur dioxide and sulfite ions, respectively, are successively increased. These equilibria also vary with the temperature. At temperatures used for pulping (130°-170°C), the actual pH value is higher than that... 

In mineral technology, sulfur dioxide and sulfites are used as flotation depressants for sulfide ores. In electrowinning of copper from leach solutions from ores containing iron, sulfur dioxide prereduces ferric to ferrous ions to improve current efficiency and copper cathode quaHty. Sulfur dioxide also initiates precipitation of metallic selenium from selenous acid, a by-product of copper metallurgy (326). 

Although acidic pulping methods have largely been displaced over the past 50 years by neutral and alkaline processes, there is still a significant amount carried out. Acid sulfite pulping uses combinations of sulfur dioxide and water at high temperatures and pressures. An appropriate base is used to control the pH and, although usually acidic, it is possible to perform these reactions at neutral or even alkaline pH. The most active nucleophile present is the bisulfite ion,... 

The concentration of sulfur dioxide, bisulfite ion and sulfite ion will be a function of pH, and the mole percent of the bisulfite ion is a maximum at around pH 4 (Figure 3.11). 

Sulfonic acids are prepared on a commercial scale by the sulfonalion of organic substrates using a variety of sulfonating agents, including sulfur trioxidc (diluted in air), sulfur trioxide (in sulfur dioxide), sulfuric acid, oleum (fuming sulfuric acid), chlorosulfuric acid, sulfamic add, trialkylamine-sulfur trioxide complexes, and sulfite ions. Other methods of sulfonic acid production, practiced on an industrial scale, include the oxidation of thiols, sulfide, disulfides, sulfoxides, sulfones, and sulfinic acids. See also Sulfonalion and Sulfation. 

Dissolved in water, sulfur dioxide produces sulfurous acid (H2S03), hydrogen sulfite ion (HSOj), and sulfite ion (SOf ). Sodium sulfite (Na2S03) has been used as a chemical food preservative, although some individuals are hypersensitive to it. 

Sulfur dioxide is not readily detectable in leaves as an inorganic residue. Thomas (25) found that plants whose leaves were exposed to sulfur dioxide accumulated sulfur in the form of sulfate and sulfite ions. The level of these inorganic ions in leaves may be related to leaf injury, but the evidence is not as clearcut as it is in leaves with accumulated fluoride. 

How many moles of sulfite ion can be converted to sulfur dioxide and water with 0.650 mol H ... 

Internal combustion produces water vapor and exhaust gases, which can condense in internal areas such as the exhaust system of automobiles [5,9]. This condensate chemis-tiy includes sulfate, sulfite, nitrate, ammonium, carbonate, bicarbonate, and chloride ions. The acidity of the condensate is high due to the presence of nitric, hydrochloric, sulfuric, and sulfurous acids. Nitric acid is formed from atmospheric nitrogen, which is converted to oxides in the engine and then to the acid. Sulfuric and sulfurous acids are formed because fuels and lubricatory oils contain sulfur, which converts to sulfur dioxide and then reacts with water vapor to form these acids. In addition, catalytic converters are designed to convert SO2 to SO3 yielding acids. Chloride additives to fuels yield hydrochloric acid. 

Sulfite ion, sulfur dioxide, and reduced sulfur compounds.180... 

Thiosulfate solutions must be standardized before their use. Sodium thiosulfate Na2S203, 5H2O is readily obtainable in a state of high purity. It is efflorescent and its water content is always uncertain. Therefore, it is unsuitable as a primary standard. Its aqueous solutions, prepared with ordinary distillated water, are not stable. Under the influence of carbon dioxide, hydrogen sulfite ions and sulfur form according to the reaction... 

Sulfur dioxide, SO2, dissolves in water to produce sulfurous acid, H2SO3 hydrogen sulfite ion, HSO3 and sulfite ion, 803 ". Because of its water solubility, sulfur dioxide is largely removed in the upper respiratory tract. It is an irritant to the eyes, skin, mucous membranes, and respiratory tract. 

Jander and coworkers used these last definitions to interpret the results of their work with liquid sulfur dioxide as solvent. Thionyl chloride is acidic, tetramethylammonium sulfite is basic, and aluminum sulfite is amphoteric in liquid sulfur dioxide. Ionization of this solvent gives thionyl and sulfite ions ... 

Calcium thiosulfate has been prepared from calcium sulfite and sulfur at 30—40°C, or from boiling lime and sulfur in the presence of sulfur dioxide until a colorless solution is obtained. Alternatively, a concentrated solution of sodium thiosulfate is treated with calcium chloride the crystalline sodium chloride is removed at low temperature. Concentrated solutions of calcium thiosulfate are prepared from ammonium thiosulfate and lime the Hberated ammonium ion is recycled to the ammonium thiosulfate process (85). 

The checkers found that the procedure of Helberger and Lan-terman,2 which avoids the use of an ion-exchange resin, is also satisfactory in case it is regarded as inconvenient to set up the resin column. According to this procedure, after completion of the reaction with sodium sulfite, anhydrous hydrogen chloride is passed into the hot solution to liberate sulfur dioxide. After removal of sulfate as in the described procedure, the undiluted aqueous solution is saturated with hydrogen chloride gas at a temperature below 25°. The precipitated sodium chloride is removed by suction filtration, the filter cake is... 

The oxidizing power of the catalytic sulfite ion/02 systems was utilized in oxidative cleavage of DNA (118-121), in an analytical application for the determination of sulfur dioxide in air (122) and in developing a luminescent probe for measuring oxygen uptake (123). 

At lower pH, sulfur dioxide is mostly present and, as the pH increases from 4 to 9, the proportion of sulfite ion increases and that of the bisulfite ion decreases. Usually either calcium or magnesium bases are used to control the pH within the acidic range. The pH is dependent upon the relative solubility of the calcium or magnesium sulfite, and upon the excess of sulfur dioxide which is used. Because of the greater solubility of magnesium sulfite, the magnesium-based... 

The scaling tendency of the lime or limestone processes for flue gas desulfurization is highly dependent upon the supersaturation ratios of calcium sulfate and calcium sulfite, particularly calcium sulfate. The supersaturation ratios cannot be measured directly. They are determined by measuring experimentally the molalities of dissolved sulfur dioxide, sulfate, carbon dioxide, chloride, sodium and potassium, calcium, magnesium, and pH. Then by calculation, the appropriate activities are determined, and the supersaturation ratio is determined. Using the method outlined in Section IV, the concentrations of all ions and ion-pairs can be readily determined. The search variables are the molalities of bisulfite, bicarbonate, calcium, magnesium, and sulfate ions. The objective function is defined from the mass balance expressions for dissolved sulfur dioxide, sulfate, carbon dioxide, calcium, and magnesium. This equation is... 

In the sulfite pulp process, the digestion fluid is typically made by dissolving sulfur dioxide in water in the presence of limestone until the solution contains 7.0% by weight S02, three-quarters of which is in the form of bisulfite ion. Why is this done In support of your answer to this question, calculate the pH of (a) the digestion solution prepared as above, (b) a hypothetical 7% solution of S02 alone, and (c) an actual saturated solution of S02 alone (2.9% S02), if the first acid dissociation constant of sulfurous acid is 1.7 x 10-2, at ambient temperature and pressure. 

Furthermore, the amphoteric behavior of the aluminum ion can be shown in sulfur dioxide as readily as in water. Just as AI(OH), is insoluble in water but dissolves readily in either a strong acid or basic solution, AMS03)3 is insoluble in liquid sulfur dioxide. Addition of either base (SO2-) or acid (SO2 ) causes the aluminum sulfite to dissolve, and it may be reprecipitated upon neutralization. 

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