Llkovic equation

To learn that in polarography, the magnitude of the diffusion current /j is proportional to analyte concentration according to the llkovic equation. 

Heyrovsky-llkovic equation Ilkovic, Dionyz Heyrovsky reaction hydrogen evolution reaction... 

This section introduces you to the factors that determine the overall rate of an electrode reaction in a system which is not stirred. This allows predictions of the shape of the resulting current/WE potential curves for a system which is under diffusion control. The work of llkovic in 1934 in deriving the current/analyte concentration relationship for the DME is covered and the llkovic equation is stated and partially derived. The Heyrovsky-Ilkovic equation (1935) is then derived this provides an explanation of the shape of the current WE potential curve. This curve now becomes a polarogram and the half-wave potential is defined and related to the polarogram. Finally the question of the reversibility of the electrode reaction is discussed and tests for reversibility are given. 

This is the Heyrovsky-llkovic equation first derived in 1935. 

We said at the beginning of 1.5.3 that the Heyrovsky-llkovic equation would be derived for a pure cathodic wave and this version of the equation took the form ... 

The question of reversibility has been discussed (1.5.4) The Heyrovsky-llkovic equation cannot be applied to an irreversible process but the trends shown in Figs. 1.5k and 1.51 are repeated as seen in Fig. 1.5m. 

SAQ 1.5c State the general form of the llkovic equation for a reduction process and explain the terms used. From this equation derive the form of the Heyrovsky-Ilkovic equation that applies to the reaction ... 

This is because n affects the shape of the polarographic wave. The Ilkovic equation tells us that there is a direct effect on the wave height, ie on The Heyrovsky-llkovic equation tells us that the value of n will affect the slope of the rising part of the wave. The greater the value of n the greater the slope, (Fig. 1.6f). 

The llkovic equation for metallic cation analysis takes the form... 

Quantitative analysis using dc polarography amounts to making use of the linear relationship between the diffusion current and the bulk analyte concentration. It may seem attractive to use the llkovic equation directly. However the diffusion coefficient (Dox) is usually not known accurately for the particular solution conditions and more important, the constant 708 emerges from the less than perfect model of the diffusion layer used in the derivation. The errors introduced are usually < 109c but this is not satisfactory for serious analytical work. 

In classical dc polarography the average current during the drop lifetime is measured. For the average current the llkovic equation becomes ... 

This equation was derived at first by Heyrovsky and llkovic [10] and is usually called the Heyrovsky-llkovic equation. In most cases, the diffusion coefficients of the Ox and Red species are not very different, so that essentially the standard redox potential. A theoretical current-potential curve in terms of versus — Uy2 shown in Figure 7.7. A semilogarithmic plot would yield a straight line (see Section 7.1.3). It should be mentioned here that Eq. (7.32) can also be applied to majority carrier processes at semiconductor electrodes (see, e.g.. Section 7.3.4). 

For the classical dropping mercury electrode, the diffusion-limited current is given by the llkovic equation... 

The classical dropping-mercury electrode (DME) represents a rather complex system. As the volume of the drop grows, its surface moves towards the solution, while the diffusion layer is also growing. As a result, the thickness of the diffusion layer is less than that which would have been calculated for a stationary electrode. Therefore, the llkovic equation is an approximation, not an exact solution of the diffusion problem. The dependence of the diffusion-limited current on t results from the combined effects of the increasing surface area (at a rate that is proportional to t / ) and the decreasing diffusion-limited current (that is proportional to r / ). 

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