Theoretical Investigation on the Concentration Dependence of the Landolt Time

Horváth, Attila; Nagypál, Ištván; Csekõ, György

doi:10.1021/jp803790e

Cited by 10 publications

(14 citation statements)

References 17 publications

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“…The mathematical background of the derivation of eqn (5) may be found elsewhere. 26 We then introduced artificial Fig. 4 Varying the starting position, while the rest of the physical parameters are the same.…”

Section: Resultsmentioning

confidence: 99%

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Imperfect mixing as a dominant factor leading to stochastic behavior: a new system exhibiting crazy clock behavior

Valkai

Horváth

2018

Phys. Chem. Chem. Phys.

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It is clearly demonstrated that the arsenous acid-periodate reaction displays crazy-clock behavior when a statistically meaningful number of kinetic runs are performed under "exactly the same" conditions. Both extensive experimental and numerical simulation results gave convincing evidence that the stochastic feature of the title reaction originates from the imperfection of the mixing process, and neither local random fluctuation nor initial inhomogeneity alone is capable of explaining adequately the observed phenomena. Imperfect mixing is manifested-in practice-in the unintentional and inherent formation of dead volumes where the concentration of the reactants may even significantly differ from the ones measured in the case of a completely uniform concentration distribution, and the system may spend enough time there under imperfectly mixed conditions to complete the nonlinear chemical process. Furthermore, it is also shown that a more efficient mixing, i.e. a smaller dead volume size and shorter residence time being spent in the dead volume, does not necessarily mean Landolt times are smaller than the one measured under completely homogeneous conditions. Evidently, the "initial" concentration of the reagents in the dead volume-and of course in the rest of the solution-greatly influences the Landolt time to be measured in the case of an individual kinetic run and may therefore show either positive or negative deviation from the Landolt time for the completely homogeneous state. As a result, less efficient mixing may either accelerate or decelerate the rate of a nonlinear autocatalytic reaction at a macroscopic volume level.

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Section: Resultsmentioning

confidence: 99%

“…Details of the derivation of eqn (6) may be found elsewhere. 26 The Landolt time (t L ) is thus calculated as t L = t i + t h . During the simulation, k 1 = 10 À5 M À1 s À1 , k 2 = 1.5 Â 10 6 M À2 s À1 , k 3 = 10 6 M À1 s À1 , P 0 = 7.0 mM, Q 0 = 10.0 mM and V total = 3.0 mL are used.…”

Section: Resultsmentioning

confidence: 99%

Imperfect mixing as a dominant factor leading to stochastic behavior: a new system exhibiting crazy clock behavior

Valkai

Horváth

2018

Phys. Chem. Chem. Phys.

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“…In addition to that the TDO–bromate system is a substrate-depletive clock reaction because the substrate (TDO) has to be totally consumed before the clock species bromine appears. Therefore, it is possible to deduce an analytical formula of the concentration dependence of the Landolt time similar to that in case of the classical Landolt reaction …”

Section: Discussionmentioning

confidence: 99%

“…dependence of the Landolt time similar to that in case of the classical Landolt reaction. 49 Concentration Dependence of the Landolt Time. To derive a formula indicating the exact concentration dependence of the Landolt time, one should consider the following simple kinetic model…”

Section: The Journal Of Physical Chemistry Amentioning

confidence: 99%

Exact Concentration Dependence of the Landolt Time in the Thiourea Dioxide–Bromate Substrate-Depletive Clock Reaction

et al. 2019

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The thiourea dioxide (TDO)–bromate reaction has been reinvestigated spectrophotometrically under acidic conditions using phosphoric acid–dihydrogen-phosphate buffer within the pH range of 1.1–1.8 at 1.0 M ionic strength adjusted by sodium perchlorate and at 25 °C. The title system shows a remarkable resemblance to the classical Landolt reaction, namely, the clock species (bromine) may only appear after the substrate TDO is completely consumed. Thus, the title system can be classified as substrate-depletive clock reaction. Despite the well-known slow rearrangement characteristic of TDO in acidic solution, it is surprisingly found that the Landolt time of the title reaction does not depend at all on the age of TDO solution applied. It is, however, shown experimentally that the inverse of Landolt time linearly depends on the initial bromate concentration as well as on the square of the hydrogen ion concentration. In addition to this, it is also noticed that dihydrogen phosphate markedly affects the Landolt time as well, and this feature may easily be taken into consideration by the H2PO4 – dependence of the rate of bromate–bromide reaction quantitatively. Based on the experiments, a simple three-step kinetic model is proposed from which a complex formula is derived to indicate the exact concentration dependence of the Landolt time.

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“…The qualitative picture of the reaction has long been accepted: , the reaction starts with a slow oxidation of hydrogen sulfite by iodate yielding an iodide ion 3 HSO 3 − + IO 3 − → 3 SO 4 2 − + 3 normalH + + normalI − followed by the well-known Dushman reaction 5 normalI − + IO 3 − + 6 normalH + → 3 normalI 2 + 3 normalH 2 normalO but no color change appears unless the reactant hydrogen sulfite is entirely consumed due to the fast oxidation of hydrogen sulfite by iodine: HSO 3 − + normalI 2 + normalH 2 normalO → SO 4 2 − + 3 normalH + + 2 normalI − Concentration dependence of the Landolt time − has been studied for several decades, but the results showed perceptible discrepancies in the relationships regarding the concentration of reactants. Recently the investigations, , however, provided a clear explanation of how these differences can be explained by the different experimental condit...…”

Section: Introductionmentioning

confidence: 99%

A Possible Candidate to Be Classified as an Autocatalysis-Driven Clock Reaction: Kinetics of the Pentathionate–Iodate Reaction

Horváth

2014

J. Phys. Chem. A

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The pentathionate-iodate reaction has been investigated by spectrophotometrically monitoring the formation of the total amount of iodine at 468 nm in the presence of phosphoric acid/dihydrogen phosphate buffer. We noticed that iodine forms only after a fairly long time lag, and the inverse of time necessary to produce a certain amount of iodine is linearly proportional to the initial concentration of iodate ion and the square of the hydrogen ion concentration, while depending complexly on the concentration of substrate pentathionate. This reaction can therefore be treated as a clock reaction but differs from the original Landolt reaction in the sense that substrate pentathionate and the clock species iodine coexist for a relatively long time--due to their relatively slow direct reaction--depending on the experimental circumstances. Furthermore, we also provided experimental evidence that iodide ion acts as an autocatalyst of the system. A 14-step kinetic model is proposed in which the mechanisms of the pentathionate-iodine, bisulfite-iodate, and the well-known Dushman reactions are combined. A thorough analysis revealed that the direct pentathionate-iodate reaction plays a role only to produce iodide ions via a finite sequence of reactions, and once its concentration reaches a certain level, the reaction is almost exclusively governed by the pentathionate-iodine and the Dushman reactions. As expected, a strong catalytic effect of the buffer composition is also found that can readily be explained by its well-known catalytic influence on the original Dushman reaction.

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Theoretical Investigation on the Concentration Dependence of the Landolt Time

Cited by 10 publications

References 17 publications

Imperfect mixing as a dominant factor leading to stochastic behavior: a new system exhibiting crazy clock behavior

Imperfect mixing as a dominant factor leading to stochastic behavior: a new system exhibiting crazy clock behavior

Exact Concentration Dependence of the Landolt Time in the Thiourea Dioxide–Bromate Substrate-Depletive Clock Reaction

A Possible Candidate to Be Classified as an Autocatalysis-Driven Clock Reaction: Kinetics of the Pentathionate–Iodate Reaction

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