Iodate-arsenous acid reaction

Florvath D and Showalter K 1995 Instabilities in propagating reaction-diffusion fronts of the iodate-arsenous acid reaction J. Chem. Rhys. 102 2471-8... 

Fig. 1.17. Different forms of travelling wavefronts (a) travelling wavefront (propagating down tube) in iodate-arsenous acid reaction with excess iodate (b) travelling wavefront or pulse in iodate-arsenous acid reaction with excess arsenite (c) target patterns in Belousov-Zhabotinskii...

A different kind of computing device is a parallel machine that can also be implemented by means of macroscopic chemical kinetics. For this purpose we choose a bistable chemical reaction, the iodate-arsenous acid reaction ... 

Suppose we take 8 CSTRs, each run as shown in fig. 4.6 with the iodate-arsenous acid reaction, eq. (4.8). Each circle is a CSTR containing this bistable reaction. The arrows indicate tube connections among the 8 tanks through which the reaction fluid from one CSTR is pumped at a set rate into another CSTR. The widths of the lines are a qualitative measure of the rate of transport from one CSTR to another. Each isolated reactor can be in one of two stable stationary states 8 reactors can be in 2 such states. By our choice of the pumping rates we determine how many stable stationary states there are in the coupled reactor system. The dark (white) circles denote a state of high (low) iodide concentration. The choices of pumping rates and stable stationary states... 

Fig. 4.5 Plot of measured (I ) versus inflow rate coefficient in the iodate-arsenous acid reaction run in an open, well-stirred system, a CSTR. The arrows indicate observed transitions from one branch of stable stationary states to the other stable branch, as the inflow rate coefficient is varied, and define the hysteresis loop. (Taken from [21] with permission.)...

The evolution of iodide, I, in the iodate-arsenous acid reaction with arsenous acid in stoichiometric excess is well described by the RD equation... 

Prove (by analytical or numerical methods) that the (logarithm of the) steady state iodide concentration as a function of the (logarithm of) / H- is as shown in Fig. 4.3, if the kinetic differential equations of the iodate-arsenous acid reaction is to be taken... 

An examples of such systems in the gas phase is the illuminated reaction S2O6F2 = 2SO3F, [7]. An example of multiple stationary states in a liquid phase (water) is the iodate-arseneous acid reaction, [8]. Both examples can be analyzed effectively as one-variable systems. 

OS 92] [R 32] [P 72/The iodate-arsenous acid reachon proceeds to one of two stationary states in different parts of the capillary when an electrical field of specific strength is applied [68]. Accordingly, a spatially inhomogeneous distribution of reaction products is generated along the capillary. 

The iodate-arsenous acid system, which we have encountered in Chapters 2 and 6, is an excellent system for study. The density changes have been measured under homogeneous conditions, and the two factors act in the same direction, that is, to decrease the density. Pojman et al. (1991b) studied simple convection in this reaction and found all the qualitative features described in the previous section. 

What about ascending fronts If a front were to propagate upward, then the hot polymer-monomer solution in the reaction zone could rise because of buoyancy, removing enough heat at the polymer-monomer interface to quench the front. With a front that produces a solid product, the onset of convection is more complicated than the cases that we considered in Chapter 9, because the critical Rayleigh number is a function of the velocity (Volpert et al., 1996). Bowden et al. (1997) studied ascending fronts of acrylamide polymerization in dimethyl sulfoxide. As in the iodate-arsenous acid fronts, the first unstable mode is an antisymmetric one followed by an axisymmetric one. Unlike that system, in the polymerization front the stability of the front depends on both the solution viscosity and the front velocity. The faster the front, the lower the viscosity necessary to sustain a stable front. 

We consider the iodate-arsenous acid system in a CSTR with arsenous acid in stoichiometric excess. A single stoichiometry describes the reaction at any time according to (I). 

In Landolt -type reactions, iodate ion is reduced to iodide tlirough a sequence of steps involving a reductant species such as bisulfde ion or arsenous acid (H AsO ). The reaction proceeds through two overall... 

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 arsenous acid-iodate reaction is a combination of the Dushman and Roebuck reactions [145]. These reactions compete for iodine and iodide as intermediate products. A complete mathematical description has to include 14 species in the electrolyte, seven partial differential equations, six algebraic equations for acid-base equilibriums and one linear equation for the local electroneutrality. 

Figure 4.101 Formation of zones due to the change of reaction mechanism by applying an electrical field during the oxidation of arsenous acid by iodate ( = 2.0 V cm" ). Numbers show the time intervals after the electric field was switched on. Intermediate product iodine (dark) and iodide (white) [68. ...

The oxidation of arsine may be accomplished by means of the halogen oxyacids and their salts,8 although not so readily as with the halogens themselves. Hypochlorites and hypobromites cause complete oxidation to arsenic acid, but side reactions are liable to occur, especially if the gas is present in excess. Chloric add slowly oxidises arsine to arsenious acid a trace of silver nitrate catalyses the reaction. Chlorates are quite inactive. More complete oxidation results with solutions of bromic acid and bromates, iodic acid and iodates, especially in the presence of catalysts. The reactions are of the type represented by the equation8... 

The induction period of the reaction may be curtailed 2 by (1) the presence of an excess of iodic acid, (2) an increase in the concentrations of the reactants, (3) the addition of a trace of arsenic acid, (4) the addition of a mineral acid and (5) exposure to sunlight. On the other hand, the period may be prolonged by the addition of mercuric chloride or by violent shaking. The proportion of the iodine liberated increases with the arsenious acid concentration and passes through a maximum. The iodine appears on the surface of the solution even though the latter may be covered with benzene (or occasionally it appears at a nucleus on the glass). The reduction of periodate to iodate by means of arsenite is a bimolecular reaction and is of the first order with respect to both components.3 At 25° C. it proceeds according to the velocity equation... 

The iodate oxidation of arsenous acid is conveniently described in terms of two component processes (De Kepper et al., 1981a Hanna et al., 1982) process A, the Dushman reaction (Dushman, 1904), and process B, the Roebuck reaction (Roebuck, 1902). 

In order to do this, we need to be clever and a little bit lucky. The most thorough analytical treatment of wave propagation in any system to date is the study by Showalter and coworkers of the arsenous acid-iodate reaction (Hanna et al., 1982). The key here is that the essential part of the kinetics can be simplified so that it is described by a single variable. If we treat one-dimensional front propagation, the problem can be solved exactly. 

Figure 6.3 (a) Measured iodide concentration as a function of time in a reaction mixture containing excess arsenous acid. Solution composition [NaI03]o = 5.00 X 10 M, [H3As03]q = 5.43 x 10 M, [H ]o = 7.1 X 10 M. (b) Simulated concentrations of iodate (short dashes), iodide (long dashes), and 350 x iodine (solid line) under the same conditions. (Adapted from Hanna et al., 1982.)... 

A model that reproduces the homogeneous dynamics of a chemical reaction should, when combined with the appropriate diffusion coefficients, also correctly predict front velocities and front profiles as functions of concentrations. The ideal case is a system like the arsenous acid-iodate reaction described in section 6.2, where we have exact expressions for the velocity and concentration profile of the wave. However, one can use experiments on wave behavior to measure rate constants and test mechanisms even in cases where the complexity of the kinetics permits only numerical integration of the rate equations. 

Bistable chemical reactions are the object of increasing interest from the experimental and theoretical points of view. The simplest abstract example is the Schlogl model well known experimental cases of bistability are the chlorite-iodide reaction or the iodate oxydation of the arsenous acid. 

Solid Compounds. The tripositive actinide ions resemble tripositive lanthanide ions in their precipitation reactions (13,14,17,20,22). Tetrapositive actinide ions are similar in this respect to Ce . Thus the duorides and oxalates are insoluble in acid solution, and the nitrates, sulfates, perchlorates, and sulfides are all soluble. The tetrapositive actinide ions form insoluble iodates and various substituted arsenates even in rather strongly acid solution. The MO2 actinide ions can be precipitated as the potassium salt from strong carbonate solutions. In solutions containing a high concentration of sodium and acetate ions, the actinide ions form the insoluble crystalline salt NaM02(02CCH2)3. The hydroxides of all four ionic types are insoluble ... 

Potassium iodate is a powerful oxidising agent, but the course of the reaction is governed by the conditions under which it is employed. The reaction between potassium iodate and reducing agents such as iodide ion or arsenic(III) oxide in solutions of moderate acidity (0.1-2.0M hydrochloric acid) stops at the stage when the iodate is reduced to iodine ... 

ESTANO (Spanish) (7440-31-5) Finely divided material is combustible and forms explosive mixture with air. Contact with moisture in air forms tin dioxide. Violent reaction with strong acids, strong oxidizers, ammonium perchlorate, ammonium nitrate, bis-o-azido benzoyl peroxide, bromates, bromine, bromine pentafluoride, bromine trifluoride, bromine azide, cadmium, carbon tetrachloride, chlorine, chlorine monofluoride, chlorine nitrate, chlorine pentafluoride, chlorites, copper(II) nitrate, fluorine, hydriodic acid, dimethylarsinic acid, ni-trosyl fluoride, oxygen difluoride, perchlorates, perchloroethylene, potassium dioxide, phosphorus pentoxide, sulfur, sulfur dichloride. Reacts with alkalis, forming flammable hydrogen gas. Incompatible with arsenic compounds, azochloramide, benzene diazonium-4-sulfonate, benzyl chloride, chloric acid, cobalt chloride, copper oxide, 3,3 -dichloro-4,4 -diamin-odiphenylmethane, hexafluorobenzene, hydrazinium nitrate, glicidol, iodine heptafluoride, iodine monochloride, iodine pentafluoride, lead monoxide, mercuric oxide, nitryl fluoride, peroxyformic acid, phosphorus, phosphorus trichloride, tellurium, turpentine, sodium acetylide, sodium peroxide, titanium dioxide. Contact with acetaldehyde may cause polymerization. May form explosive compounds with hexachloroethane, pentachloroethane, picric acid, potassium iodate, potassium peroxide, 2,4,6-trinitrobenzene-1,3,5-triol. 

EXPLOSION and FIRE CONCERNS flammable in the form of dust when exposed to heat or flame when heated or on contact with acid or acid fumes, it emits highly toxic fumes dangerous when water solutions of arsenicals are in contact with active metals such as iron, zinc, aluminum flammable by chemical reaction with bromates, chlorates, iodates, peroxides, lithium, silver nitrate, nitric acid, potassium permanganate, chromium trioxide, chlorine trifluoride, chlorine oxide, bromine trifluoride, bromine pentafluoride, bromine azide use foam, carbon dioxide, or dry chemical for firefighting purposes.. 

Arsenic(III) oxide (AS2O3) is available in pure form and is a useful (and poisonous) primary standard for many oxidizing agents, such as Mn04. AS2O3 is first dissolved in base and titrated with MnOJ in acidic solution. A small amount of iodide (F) or iodate (10J) is used to catalyze the reaction between H3ASO3 and MnO. The reactions are... 

The actinide ions in aqueous solution resemble the tripositive lanthanide ions in their precipitation reactions, allowing for differences in the redox properties of early members of the actinide series. The chloride, bromide, nitrate, bromate, and perchlorate anions form water-soluble salts, which can be isolated as hydrated solids by evaporation. The acetates, iodates, and iodides are somewhat less soluble in water. The sulfates are sparingly soluble in hot solutions, somewhat more soluble in the cold. Insoluble precipitates are formed with hydroxide, fluoride, carbonate, oxalate, and phosphate anions. Precipitates formed from aqueous solution are usually hydrated, and the preparation of anhydrous salts from the hydrates without formation of hydrolyzed species can only be accomplished with difficulty. The actinide(iv) ions resemble Ce(iv) in forming fluorides and oxalates insoluble even in acid solution. The nitrates, sulfates, perchlorates, and sulfides are all water-soluble. The iv state actinide ions form insoluble iodates and arsenates even in rather strong acid solution. The... 

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