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The paper refers to disproportionation of HIO and NaIO in aqueous media, in static and dynamic systems. The results of calculations, realized according to GATES/GEB principles, with use of an iterative computer program, are presented graphically. An example of the computer program with all physicochemical knowledge involved in the related algorithm is attached herewith.

Quantitative description of electrolytic redox systems is performed by means of electron, charge and concentration balances, and a complete (not contradictory) set of relations for equilibrium constants, related to the system in question. The electron balance, termed as the Generalized Electron Balance (GEB) obtained according to Approach II to GEB, stems from linear combination 2∙f(O)-f(H) of the elemental balances: f(H) for H, and f(O) for O [_{2}O) media. The GEB is the immanent part of the Generalized Approach to Electrolytic Systems (GATES); the computer software applied to redox systems is denoted as GATES/GEB [

Some elements form compounds and species at three or more oxidation degrees. In particular, iodine forms the species on six oxidation degrees

From the preliminary, laconic information [_{3} + 2I_{2} + 2H_{2}O (in the original notation applied there) and its salts rapidly disproportionate to form iodides and iodates. This information will be verified on the basis of the results of calculations, presented graphically on the corresponding speciation diagrams.

Information about kinetics of HIO disproportionation was presented in [

In the present paper, we refer to disproportionation of hypoiodous acid, HIO, and its salt NaIO; oxidation degree

The static systems with C solutions of (1) HIO and (2) NaIO are shown graphically in Figures 1(a)-(c) and Figures 2(a)-(c) with the values pC = −logC on the abscissa. The static system indicate pH, E and

As results from speciation diagram in

with further dilution of HIO solution, reaction (2b) is accompanied, in an increasing degree, by the reaction

The change in disproportionation scheme, more significant at pC 4 - 5, resulted in a change of the shapes of the plots: E = E(pC) (

For different pC values, the disproportionation in C mol/L NaIO proceeds there mainly according to the scheme (see

where

During the dilution of equimolar mixture of HIO (C = 0.1 mol/L) + NaIO (C = 0.1 mol/L) with water, in the range of higher C (i.e., lower pC) values we have the disproportionation reactions:

occurring there predominantly, in a comparable degree. Reactions involving IO^{−} occur in a much lesser extent. At pC > 2.40,

The curve E = E(pC) passes through a maximum (

a minimum (

In dynamic systems, the related curves will be plotted on graphs with the fraction titrated

related to addition of V mL of titrant T (C mol/L B) into V_{0} mL of titrand D (C_{0} mol/L A); A, B―reagents.

The curves plotted at V_{0} = 10 mL, C_{0} = 0.01 mol/L and C = 0.1 mol/L, are presented in Figures 4(a)-(c).

At the initial part of the titration we have the reactions:

In the following, at Φ ca. 0.20 - 0.22, a pronounced increase in [I^{−}] occurs, as a result of reaction

The increase in [I^{−}] is accompanied by an increase in

This leads to the gradual disappearance of

At_{2}] = s = const; s = 1.33 × 10^{−3} mol/L is the solubility of

Note that the stoichiometry of the reaction (13) is 3:3 = 1:1, which corresponds to the jump on the curves (4b) and (4c), occuring at Φ = 1. For Φ > 1, we have

The curves plotted at V_{0} = 10 mL, C_{0} = 0.01 mol/L NaIO and C = 0.1 mol/L HCl are presented in Figures 6(a)- (d). Initially, the reaction

and then the reaction

occur. Then I^{−} from (14) and I_{2} from (15) form

At_{2}] = const, as well. The increase in [Cl^{−}], resulted from addition of HCl, causes an

increase in [I_{2}Cl^{−}], and—to a lesser extent—the increases in ^{−}]; [HIO_{3}] also increases. In effect, the summary concentration [HIO] + [IO^{−}] after addition of an excess of HCl is higher than in the starting NaIO solution.

In the algorithm (see Appendix), we have allowed the participation of Cl^{−} ions from HCl solution in the redox reaction. However, the concentration of Cl_{2} and HClO as the main products of Cl^{−} oxidation (

quite negligible. This way, one can state that the Cl^{−} ions practically do not participate the redox reaction as a reducing agent. From linear combination of reactions: (14) and

(multiplication by 5 and 2 resp.), cancellations and division by 3, we get the reaction

with stoichiometry 4:5 = 0.8, which corresponds to Φ = 4/5 = 0.8, where the inflection point on the curves in

see

The disproportionation reactions in the static and dynamic systems with (a) HIO, (b) NaIO, (c) HIO + NaIO were considered. The static systems were equivalent, in principle, with dynamic systems where the related titrand was diluted with pure water. In the dynamic system where NaIO solution was titrated with HCl, chlorine (Cl) was considered as a second “player”, i.e., possibility of oxidation of Cl^{−}-ions was admitted/pre-assumed. However, as stated on the basis of results of calculations, the concentrations of Cl_{2} and HClO as the main products of Cl oxidation are extremely low. On this basis, it can be considered that the IO^{−} introduced into the system as NaIO, undergoes disproportionation (not a reduction) reaction. All these calculations were made under assumption that the relevant reactions take place in quasi-static manner, under isothermal conditions. The reactions proceeding in the respective systems were formulated under assumption that all equilibrium constants found in the relevant tables (see Appendix) and then used in the calculations are correct.