Potassium redox reactions

The most common water-soluble initiators are ammonium persulfate, potassium persulfate, and hydrogen peroxide. These can be made to decompose by high temperature or through redox reactions. The latter method offers versatility in choosing the temperature of polymerization with —50 to 70°C possible. A typical redox system combines a persulfate with ferrous ion ... 

When the potassium permanganate Is added, a redox reaction occurs (the equation for the reaction Is derived and balanced In the text). 

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 ... 

When we mix two solutions the result is often simply a new solution that contains both solutes. However, in some cases the solutes can react with each other. For instance, when we mix a colorless aqueous solution of silver nitrate with a clear yellow aqueous solution of potassium chromate, a red solid forms, indicating that a chemical reaction has occurred (Fig. 1.1). This section and the next two introduce three of the main types of chemical reactions precipitation reactions, acid-base reactions, and redox reactions, all of which are discussed in more depth in later chapters. (The fourth type of reaction discussed in this text, Lewis acid-base reactions, is introduced in Section 10.2.) Because many chemical reactions take place in solution, particularly in water, in this section we begin by considering the nature of aqueous solutions. 

Write the balanced chemical equation for (a) the thermal decomposition of potassium chlorate without a catalyst (b) the reaction of bromine with water (c) the reaction between sodium chloride and concentrated sulfuric acid, (d) Identify each reaction as a Bronsted acid—base, Lewis acid—base, or redox reaction. 

The reactivities of potassium and silver with water represent extremes in the spontaneity of electron-transfer reactions. The redox reaction between two other metals illustrates less drastic differences in reactivity. Figure 19-5 shows the reaction that occurs between zinc metal and an aqueous solution of copper(II) sulfate zinc slowly dissolves, and copper metal precipitates. This spontaneous reaction has a negative standard free energy change, as does the reaction of potassium with water ... 

Formaldehyde gas for disinfection purposes may be released from the aqueous solution ( formalin ) by treatment with potassium permanganate (the heat for evaporation arising from the redox reaction), but the quantities must be limited to avoid... 

Sodium thiocyanate See Potassium thiocyanate, above See other redox reactions... 

In the literature the term soluble Prussian blue introduced by Keggin and Miles [5] to determine the KFeFe(CN)6 compound is still widely used. However, it is important to note, that the term soluble refers to the ease with which the potassium ion can be peptized rather than to the real solubility of Prussian blue. Indeed, it can be easily shown by means of cyclic voltammetry that the stability of Prussian blue films on electrode supports is nearly independent of their saturation by potassium cations. Moreover, Itaya and coworkers [9] have not found any appreciable amount of potassium ions in Prussian blue, which makes doubtful structures like KFeFe(CN)6. Thus, the above equation fully describes the Prussian blue/Prussian white redox reaction. 

The participation of cations in redox reactions of metal hexacyanoferrates provides a unique opportunity for the development of chemical sensors for non-electroactive ions. The development of sensors for thallium (Tl+) [15], cesium (Cs+) [34], and potassium (K+) [35, 36] pioneered analytical applications of metal hexacyanoferrates (Table 13.1). Later, a number of cationic analytes were enlarged, including ammonium (NH4+) [37], rubidium (Rb+) [38], and even other mono- and divalent cations [39], In most cases the electrochemical techniques used were potentiometry and amperometry either under constant potential or in cyclic voltammetric regime. More recently, sensors for silver [29] and arsenite [40] on the basis of transition metal hexacyanoferrates were proposed. An apparent list of sensors for non-electroactive ions is presented in Table 13.1. 

Some of the investigations carried out in the first half of the twentieth century were related to CL associated with thermal decomposition of aromatic cyclic peroxides [75, 76] and the extremely low-level ultraviolet emission produced in different reaction systems such as neutralization and redox reactions involving oxidants (permanganate, halogens, and chromic acid in combination with oxalates, glucose, or bisulfite) [77], In this period some papers appeared in which the bright luminescence emitted when alkali metals were exposed to oxygen was reported. The phenomenon was described for derivatives of zinc [78], boron [79], and sodium, potassium, and aluminum [80]. 

The concept of reduction potential is introduced in Chapter 6. When the reduction potentials of two species differ by 0.1 V or more, the resulting redox reaction will proceed rapidly and stoichiometrically so that it may be used as the basis for a titrimetric procedure. The end point of a redox titration may be observed by following the potential of the titrand with an indicator electrode or with a visual indicator. In two special cases, the reagent (potassium permanganate and iodine) is self-indicating (vide infra). 

Decomposition reactions are reactions in which a compound breaks down into two or more simpler substances. Although not all decomposition reactions are redox reactions, many are. For example, the thermal decomposition reactions, such as the common laboratory experiment of generating oxygen by heating potassium chlorate, are decomposition reactions ... 

Grey potassium metal, which is stored under oil, reacts very vigorously with greenish-yellow chlorine gas to form white potassium chloride. The changes in oxidation numbers show that this synthesis reaction is also a redox reaction. 

In the Breathalyzer test, the subject blows into a tube connected to a vial. The exhaled air collects in the vial, which already contains a mixture of sulfuric acid, potassium dichromate, water, and the catalyst silver nitrate. The alcohol reacts with the dichromate ion in the following redox reaction. 

Case 1 appears to accurately predict the observed dependence on persulfate concentration. Furthermore, as [Q]+otal approaches [KX], the polymerization rate tends to become independent of quat salt concentration, thus qualitatively explaining the relative insensitivity to [Aliquat 336]. The major problem lies in explaining the observed dependency on [MMA]. There are a number of circumstances in free radical polymerizations under which the order in monomer concentration becomes >1 (18). This may occur, for example, if the rate of initiation is dependent upon monomer concentration. A particular case of this type occurs when the initiator efficiency varies directly with [M], leading to Rp a [M]. Such a situation may exist under our polymerization conditions. In earlier studies on the decomposition of aqueous solutions of potassium persulfate in the presence of 18-crown-6 we showed (19) that the crown entered into redox reactions with persulfate (Scheme 3). Crematy (16) has postulated similar reactions with quat salts. Competition between MMA and the quat salt thus could influence the initiation rate. In addition, increases in solution polarity with increasing [MMA] are expected to exert some, although perhaps minor, effect on Rp. Further studies are obviously necessary to fully understand these polymerization systems. 

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 ... 

It is an oxidizing agent and undergoes redox reactions with reducing agents. Its oxidizing action, however, is weaker to that of potassium chlorate. Thus the salt is unable to oxidize the iodide ion to iodine in acid medium. 

Redox reactions that have a positive reaction free energy are not spontaneous, but electricity can be used to make them occur. For example, there is no common spontaneous chemical reaction in which fluorine is a product, so the element cannot be isolated by any common chemical reaction. It was not until 1886 that the French chemist Henri Moissan found a way to force the formation of fluorine by passing an electric current through an anhydrous molten mixture of potassium fluoride and hydrogen fluoride. Fluorine is still prepared commercially by the same process. 

An alternative to the oxidation-number method for balancing redox reactions is the half-reaction method. The key to this method is to realize that the overall reaction can be broken into two parts, or half-reactions. One half-reaction describes the oxidation part of the process, and the other half-reaction describes the reduction part. Each half is balanced separately, and the two halves are then added to obtain the final equation. Let s look at the reaction of aqueous potassium dichromate (K2Cr2C>7) with aqueous NaCl to see how the method works. The reaction occurs in acidic solution according to the unbalanced net ionic equation... 

This reaction of an ionic hydride with water is a redox reaction because the hydride reduces the water (4-1 oxidation state for H) to H2 (0 oxidation state). In turn, the hydride (—1 oxidation state for H) is oxidized to H2. In general, ionic hydrides are good reducing agents. Some, such as potassium hydride, catch fire in air because of a rapid redox reaction with oxygen ... 

This decomposition is a redox reaction in which the oxygen in K02 is simultaneously oxidized from the -1 /2 oxidation state in 02 to the 0 oxidation state in 02 and reduced from the -1/2 oxidation state in 02 to the -1 oxidation state in H02-. A reaction in which a substance is both oxidized and reduced is called a disproportionation reaction. One useful consequence of the K02 disproportionation reaction in water is that potassium superoxide can serve as a convenient source of oxygen in masks worn by firefighters. The oxygen results from reaction of K02 with exhaled water vapor. 

The redox reaction of the ferrocene moiety in a 6-(ferrocenyl)hexanethiol-hexanethiol (FcCgSH Q,SH, 1 20) mixed monolayer has been studied in the presence of potassium ferrocyanide as reducing agent. Thus, the ferrocenium formed at anodic potentials is reduced to ferrocene by the ferrocyanide in solution and the whole process becomes a surface catalytic reaction, in agreement with the following reaction scheme ... 

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