Sodium thiosulfate , REDOX

The amount of sodium hypochlorite in a bleach solution can be determined by using a given volume of bleach to oxidize excess iodide ion to iodine CIO- is reduced to Cl-. The amount of iodine produced by the redox reaction is determined by titration with sodium thiosulfate, Na2S203 I2 is reduced to I-. The sodium thiosulfate is oxidized to sodium tetrathionate, Na2S406. In this analysis, potassium iodide was added in excess to 5.00 ml of bleach d = 1.00 g/cm3). If 25.00 mL of 0.0700 MNa2S203 was required to reduce all the iodine produced by the bleach back to iodide, what is the mass percent of NaCIO in the bleach ... 

Perhaps this may be considered in relation to the suggestion of Kellermeyer et al. (K5) that the drugs involved are transformed in vivo to redox intermediates. Furthermore, the reducing capacity of RBC was shown to be a function of GSH content. Reduction of this capacity by intravenous infusion of sodium thiosulfate solution reflects changes in the intracellular oxidation-reduction system of glutathione, the oxidized form being favored (Cl, S9). 

Elemental composition K 23.41%, Br 47.85%, O 28.74%. Aqueous solution of the salt after sufficient dilution may be analyzed for its potassium content by AA, ICP, or flame photometry (see Potassium) and for bromate anion by ion chromatography. Also, bromate content can be measured by iodometric titration using a standard solution of sodium thiosulfate and starch as indicator. The redox reactions are as follows ... 

How can one verify, just by looking at the Latimer diagram of silver, that sodium thiosulfate (hypo) is useful in photographic processes that require the removal of excess, wrested silver halide Is this process (fixing) actually a redox reaction Explain... 

Redox titrations are often performed for metal analysis. Metals in their lower oxidation states are common reducing agents. This includes Fe2+, Sn2+, Mo3+, W3+, Ti3+, Co2+, U4+, and V02+. Sodium thiosulfate, (Na2S203) is one of the most widely used reductants in iodometric titrations. Other reducing agents include sodium arsenite and phenylarsine oxide. Iodometric titration is discussed separately in the next section. 

Other REDOX reagents include iodine (I2), either by itself in a forward titration or in a back titration with sodium thiosulfate (Na2S2Os), and complex salts of the metal cerium (such as ammonium cerium sulfate,... 

So-called Raffo or LaMer sulfur sols are used most frequently. These can be prepared by dropwise addition of aqueous sodium thiosulfate to concentrated sulfuric acid followed by coohng and precipitation of the hydrophilic sol by a saturated solution of sodium chloride. The sol originates from the spontaneous decomposition of the primary product thiosulfuric acid (H2S2O3) which disproportionates in a series of complex redox reactions producing elemental sulfur, hydrogen sulfide, sulfur dioxide and polythionic acids ... 

Figure 4.63. Redox titration of potassium triiodide by thiosulfate with starch added as indicator to the reagent stream R (5 x 10 M sodium thiosulfate) using the manifold depicted in Fig. 4.62a and the conditions stipulated there. All samples (C = 0.25, 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, and 10.0 mM KI3) were each injected in triplicate and monitored spectrophoto-metrically at 610 nm. The At values were read off at the Eq level.

Sodium thiosulfate (NajSjOj 5H2O) solution reacts with aqueous iodine in a redox reaction accordingto the equation... 

Figure 5.3. Growth of vitamin Bn-depleted and vitamin Bn-deficient cells ofP. shermanii in different redox environments. A wild-type cells deprived of cobalt (residual vitamin B about 10 pg/g) were grown in the absence of cobalt (1), under argon gas (2) or in the presence of C0CI2 6H2O at 3 mg/1 (3). In 3, the fmal level of vitamin B12 was 1500 pg/g. B vitamin Bi2-deficient mutant cells were grown in the absence of cobalt (1), but in the presence of 0.03% each of the following reduced glutathione (2), sodium thiosulfate (3), cysteine (4), methionine (5) or tryptone (6). From Iordan et al. (1984).

A common redox reaction is the reaction of an oxidizing agent with excess potassium iodide solution to form iodine. The iodine is then titrated with sodium thiosulfate solution, using starch as an indicator (Figure 9.15). 

Several methods are based on the redox character of the iodide ions. They can be oxidized to iodine and titrated with sodium thiosulfate or phenylarsin oxide titrant. The oxidation can be made in acidic medium [73]. The excess of the oxidizing agent can be taken away by adding urea into the solution. Bromide ions interfere with this method. 

The polymerization of calcium acrylate may be initiated with typical redox systems such as ammonium persulfate-sodium thiosulfate and certain peroxides with reducing agents such as sodium thiosulfate. Hydroxylamine hydrochloride, hydrazine hydrate, and tetramethylenepentamine are also suitable reducing agents with certain oxidizing agents [110]. 

The oxidation states of S are +2 in 8203 , 0 in S, and +4 in SO2. Thus, 8203 is simultaneously oxidized and reduced. 8olutions of sodium thiosulfate (Na2S203) are often used in the laboratory in redox reactions, and stock solutions of Na2S203 sometimes develop small deposits of sulfur, a pale yellow solid, over time. 

Sodium tetrathionate (Na2S406) is a redox compound that under the right conditions can facilitate the formation of disulfide bonds from free sulfhydryls. The tetrathionate anion reacts with a sulfhydryl to create a somewhat stable active intermediate, a sulfenylthiosulfate (Fig. 102). Upon attack of the nucleophilic thiolate anion on this activated species, the thiosulfate (S203 =) leaving group is removed and a disulfide linkage forms (Pihl and Lange, 1962). The reduction of tetrathionate to thiosulfate in vivo was a subject of early study (Theis and Freeland, 1940 Chen et al., 1934). 

Lead tetraacetate consumption is measured conveniently by iodometry.4 The reaction mixture is added to excess potassium iodide solution, usually in the presence of sodium acetate,6 and the iodine liberated is then titrated with standard thiosulfate. Oxidation may also be measured potentiometri-cally,78 210 211 a procedure especially useful for fast glycol groups,78 or with redox indicators.211... 

Many redox reactions by colloidal nanoparticles have been reported. Three of the most-studied reactions are (1) the catalyzed electron transfer between ferricyanide and thiosulfate [8,19-21], (2) the catalytic reduction of fluorescent dyes by sodium borohydride [22, 23], and (3) the catalytic reduction of organic compounds (e.g., nitro-aryls [9] and alcohols [24]). These reactions have been studied extensively because they are easy to follow spectroscopically allowing for straightforward measurement of reaction kinetics. The third set of reactions has enormous industrial significance, where nitro compounds are reduced to their less toxic nitrate or amine counterparts [25, 26] and the electrooxidation of methanol is utilized for methanol fuel cells [27, 28]. 

There have been fewer reports on the particle size dependence of catalysis by platinum-catalyzed redox reactions. A report by Sharma et al. [21] showed that platinum colloidal nanoparticles do not demonstrate the same dependence on particle size as gold nanoparticles do for the reduction of hexacyanoferrate (III) by thiosulfate [19]. Platinum nanoparticles protected by sodium di(2-ethylhexyl) sulfosuccinate (synthesized by a reverse micelle technique) exhibit an optimum size ( 38 nm) for the reduction of ferricyanide by thiosulfate (Fig. 18.2). The reason for an optimum particle size is not fully understood however, they proposed the following explanation a shift in the Fermi level occurs as the diameter is increased. 

The mixing time can be determined by chemical means, if the tank contents is mixed with a reaction component and the component to be added is mixed with a (1 4- x)-fold equivalent of the second reaction component, so that after intimate mixing the two reaction partners react with one another. The disappearance of the reaction partner is shown by a color indicator, which experiences a sudden color change. ( Method of the last color change is used, in contrast with decolorizing reaction which is proportional to the degree of conversion, see e.g. Kappel [262]). The redox reactions of thiosulfate with iodine (indicator starch) and the neutralization of sodium hydroxide with sulfuric acid (indicator phenolphthalein) have been found to be simple fast ionic reactions, suitable for this purpose. 

Solutions of Sodium and Potassium Sulfite and Bisulfite. Oxygen free, pure sulfite and bisulfite solution containing sodium or potassium ions are stable for more than a year at room temperature. However, at 100°C or above, the sulfate spectrum can be observed already after a few days. Elemental sulfur does not immediately appear. Sometimes, at intermediate and high pH, thiosulfate can be observed in a few experiments. The appearance of these species indicates that they are intermediates in the auto-redox reaction Equations I-III, or that they are formed in a secondary reaction of sulfur (IV) with the product elemental sulfur. The latter reactions are already known. They occur during the degradation of elemental sulfur... 

Sodium nitroprusside undergoes a redox reaction that releases cyanide (6,9). The cyanide that is produced is rapidly converted into thiocyanate in the liver by the enzyme thiosulfate sulfotransferase (rhodanase) and is excreted in the urine (6,9). The rate-limiting step in the conversion of cyanide to thiocyanate is the availability of sulfur donors, especially thiosulfate. Toxic symptoms of thiocyanate begin to appear at plasma thiocyanate concentrations of 50 to 100 mg/mL. The elimination half-life of thiocyanate is 2.7 to 7.0 days when renal function is normal but longer in patients with impaired renal function. 

Most kinetic determinations of anions involve the iodide ion, which exhibits a strong catalytic effect on the reaction between cerium(IV) and arsenic(III) and a few others as a result of the redox properties of the I2/ I couple. Other anions that can be determined using their intrinsic catalytic effect include sulfur-containing species such as sulfite, sulfide, and thiosulfate, which are quantified by means of the iodine/sodium azide system, and phosphates, which are measured through their effect on the formation of molybdenum blue. Table 5 gives illustrative examples of determinations for these anions and a few others. 

The compound is precipitated by an excess of a standardized solution of potassium bichromate. The excess bichromate is titrated by adding sodium iodide. The liberated iodine is titrated by thiosulfate. Thus, the quantitative reaction exhibited by ethacridine lactate is not a redox reaction. It is a precipitation reaction. 

As in all liquid-redox processes, part of the sulfur is converted to thiosulfate, although the rate of formation is appreciably lower in the essentially neutral Thylox solution than in more alkaline solutions used in other processes. Hydrogen cyanide, which is absorbed in the absorber, reacts readily with the sulfur formed in the thionizer to yield sodium thiocyanate. Because of these side reactions, the active thioarsenate has to be replenished continuously by addition of arsenic oxide and sodium carbonate. 

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