Oxygen, determination equilibrium concentrations

It is necessary to estimate the quantity of each gas in the liquid to accurately determine the productivities and usage rates. The species equilibrium concentration, x, in the liquid is estimated by Henry s Law (Eq. 3). Unfortunately, H, the Henry s Law constant, for a gas in contact with a solution depends on the nature and concentrations of dissolved solids, tending to be less than the value for pure water [71]. For this reason, we can only obtain an upper limit for the dissolved gas quantity. However, the solubility depression for our rather dilute culture medium is low. A 0.5 mole/1 concentration of sodium chloride results in an oxygen solubility depression of 15 % [71]. The total concentration of dissolved solids in our medium was less than half of that (0.22 mole/1), so the gas solubility depression was almost certainly less than 10%. A more serious uncertainty occurs because the culture volume includes cell volume by treating the entire 83 ml as liquid volume (V ), we may tend to overestimate the dissolved gas quantity. 

The Chreedimensional diagram obtained could serve both theoretical and technological computations concerning oxygen enrichment of air on K-clinoptilolite. It is a basis for determining of adsorption isobars, fictitious and real isotherms, as well as thermodynamic data for adsorption from binary C /Nj mixtures. Freundlich and Henry constants (for the real adsorption isotherms) correlated with the equilibrium concentration are useful for computation of the amounts adsorbed at arbitrary partial pressures and equilibrium concentrations. 

Thus, the presence of the inflection point in the calibration E-pO plots is a distinctive feature of the work on the gas membrane oxygen electrode in high-temperature ionic melts. More exactly, there are two linear sections, with slopes corresponding to values of z equal to 1 and 2. This result, noted at first in our paper [233], showed that the electrode process at the gas membrane oxygen electrode was essentially dependent not on peculiarities of the assumed potential-determining process with the participation of the given Lux base (as was considered before), but on the equilibrium concentration of oxide ion created by dissociation of this base in the ionic melt. 

All the routines described for the determination of the thermodynamic (concentration) parameters in metal oxide solutions include some indirectly obtained values. For example, the equilibrium concentration of metal cations is calculated proceeding from the quantity of the oxide-ion donor consumed for titration (precipitation). Direct determination of the concentration of metal cations in the melt (if it is possible) allows one to obtain more correctly the obtained solubility product values. Our paper [332] reports a method for correction of the solubility product values for oxides on the basis of the potentiometric titration data. The modification of the standard routine consists of the simultaneous use of two indicator electrodes, one of which is the membrane oxygen electrode and the other is a metal electrode, reversible to the cations the oxide consists of. This routine was used to estimate the solubility products of copper(I) and nickel(II) oxides in the molten KCl-NaCl equimolar mixture at 700 °C. Investigation of Cu20 by the proposed method is of considerable importance since, as will be shown further, the process of dissociation/dissolution of copper(I) oxide in molten alkali-metal halides differs from the generally accepted one which was considered, e.g. in Ref. [119]. 

At moderately high CO partial pressures and low O2 partial pressures, e.g., pco = 0 05 atm and po2 = 0.1 atm, the concentration of adsorbed oxygen atoms is considerably lower than the equilibrium concentration and the rate is determined by the dissociation of oxygen molecules, reaction (V.32), and the side reaction (V.38),... 

Under conditions of oxygen or electrolyte concentration gradients, or due to heterogeneities of the metallic substrate, the cathodic and anodic sites may be separated. For each of the two electrodes, the equilibrium potential for their actual conditions can be determined by the Nemst equation. The electromotive force (EMF) for the corrosion process to occur is the difference between the two equilibrium potentials. When the cathode and the anode are short-circuited, a mixed potential results, known as corrosion potential, f corr- The value of corr lies between the two separate electrode potentials, although shifted towards the equilibrium potential of the faster reaction. This situation can be easily visualized with the help of the... 

Using the Henry s Eaw model in the simulator available to you, determine the concentration of oxygen (ppm by mass) in water at 10°C and 27°C if the water is in equilibrium with air. Conpare the results obtained to those calculated using the SRK model with the BIPs available in the simulator databank. 

Weaver calculated the open circuit potentials of these and other possible reactions that might occur under open circuit conditions, finding agreement between measured potentials and the potentials calculated from thermodynamic tables (Weaver et al, 1979). Hemmes and Cassir (2004) recalculated the cell open circuit potentials. They determined the equilibrium concentrations and electrode potentials in a system comprised of carbon, carbonate, CO2, CO, O ", and electrons, using the phase rule modified for electrochemical systems by Coleman and White (1996). Hemmes expressed the half-cell potentials of the anode reactions (3) and (4) referenced to an idealized cathode reaction (unit oxygen and CO2 partial pressures) ... 

The oxygen transfer rate is calculated based on oxygen concentration gradient, by determination of the oxygen level in the liquid phase and the equilibrium value. 

At mercury and graphite electrodes the kinetics of reactions (15.21) and (15.22) can be studied separately (in different regions of potential). It follows from the experimental data (Fig. 15.6) that in acidic solutions the slope b 0.12 V. The reaction rate is proportional to the oxygen partial pressure (its solution concentration). At a given current density the electrode potential is independent of solution pH because of the shift of equilibrium potential, the electrode s polarization decreases by 0.06 V when the pH is raised by a unit. These data indicate that the rate-determining step is addition of the first electron to the oxygen molecule ... 

It follows from the equation (3.28) that the liquid technique to determine concentration of dissolved oxygen or oxygen of extraneous gases being analyzed (nitrogen, hydrogen, inert gases, hydrocarbons, etc.) which are in equilibrium with liquid polar solvent (water, alcohols, etc.), is applicable as well. This means that relation... 

---