Magnesium activity coefficients

No specific ionic selectivity is really admitted in pectins with monovalent counterions due to the relativity low charge parameter a very interesting behaviour is observed when divalent counterions are considered. Specially, it was demonstrated that when DM<50% the activity coefficient of magnesium is much larger than that of calcium. The transport parameters (f) were found following the order [45] ... 

With different pectins, one found that the activity coefficient of calcium has a value half that of magnesium this is interpreted as the basis of a dimer formation in presence of calcium. The specific interaction of calcium was described as the egg-box model first proposed for polyguluronate in which oxygen atoms coordinated to calcium [46]. Recently, the comparative behaviour of Mg and Ca with homogalacturonan was reexamined [47]. 

Excluding activity coefficients, three relationships are required in addition to the nine thermodynamic equilibria in order to calculate concentrations of the 12 unknown species. These relationships are the mass balances for magnesium and chloride, and the electroneutrality equation. 

The observation that calcium and magnesium ion activity coefficients are generally similar in aqueous solution has led to the concept that the calcium to magnesium ion concentration ratio should be fixed at a given temperature and... 

The goal of this research was to improve activity coefficient prediction, and hence, equilibrium calculations in flue gas desulfurization (FGD) processes of both low and high ionic strength. A data base and methods were developed to use the local composition model by Chen et al. (MIT/Aspen Technology). The model was used to predict solubilities in various multicomponent systems for gypsum, magnesium sulfite, calcium sulfite, calcium carbonate, and magnesium carbonate SCU vapor pressure over sulfite/ bisulfite solutions and, C02 vapor pressure over car-bonate/bicarbonate solutions. 

The large value for the rate coefficient compared with those given in Table 10 raises the point as to whether it results from very high activity of catalytic sites, from a high proportion of active centres, or from a combination of both effects. The efficiency of the magnesium activated catalysts (obtained from Rpt/P vs. t) gives a value of / 0.5 [297]... 

J.A. Rard, D.G. Miller, Isopiestic determination of the osmotic and activity coefficients of aqueous magnesium chloride solutions at 25... 

The primary solubility data and the calculation of the solubility products, defined in the usual way, are presented. This presentation contains some unexpected results. The total solubility of the metal ion and selenite are approximately equal in water and in the inert salt solutions for the magnesium and manganese selenites. This is the expected result for a simple dissolution reaction. For calcium selenite, the metal ion concentration was about 100 times greater than the total selenite concentration whereas for zinc selenite the opposite was found. There is no comment in the paper on these results, which contradict the equilibrium reactions used in the paper to define the reported solubility products for calcium and zinc selenite. The review also noted that the calculation of the magnesium and selenite activities from the total concentrations introduces activity coefficients between 0.1 to 0.01 at moderate ionic strengths. Thus the values of these coefficients appear unreasonably small. On the whole, the activity coefficient corrections introduced appear to vary in an erratic way between the various systems studied. 

ISO] Isono, T., Osmotic coefficients, stoichiometric activity coefficients, and dissociation constants of magnesium and nickel sulfates in aqueous solutions at the freezing-point, Rikagaku Kenkyusho, 65, (1971), 95-99. Cited on pages 181, 183, 188, 189,347. 

A thermodynamic model developed by Barba, Brandani and di Giacomo (1982) described the solubility of calcium sulphate in saline water. A system of equations based on Debye Hiickel and other models was used to describe isothermal activity coefficients of partially or completely dissociated electrolytes. Using binary parameters, good agreement was claimed between experimental and predicted values of calcium sulphate solubility in sea water and brackish brines including those with a magnesium content. 

Comparatively low levels of other ionic components in serum, like potassium and magnesium which comprise less than 6 per cent of the total ionic strength of blood serum, have a negligible effect on the activity coefficient of calcium ions at ionic strengths below 1.0 mol dm [38]. The activity coefficients of these ions can be expected to be affected by the high sodium level as with calcium. 

Ion-selective electrodes offer an observable value for the biologically relevant parameter the ion s active molality in the aqueous phase of the biological specimen directly. This might be a challenge for elements that are associated by 30-50% to different anions, e.g., magnesium and calcium. For alkaline and alkaline-earth metal cations the Debye-Hiickel formalism allows a fair approximation of the mean activity coefficient ji+ as measured for an ion and its counterion in a calibration solution. The notation of... 

Scatchard. G. Y.C. Wu. R.M. Rush. "Osmotic and activity coefficients for binary mixtures of sodium chloride, sodium sulfate, magnesium sulfate and magnesium chloride in water at 25°C. III. Treatment with the ions as components", J. Phys. Chem., v74, 21, pp3786-3796 (1970)... 

This introduction allowed Lewis and Randall to determine the values of the activity coefficients of some individual ions, in different solutions. Some are given in Table 3.1. designates a bivalent cation with a metal origin such as alkahne earth metals, magnesium, copper, cadmium or zinc. 

Calculate the activity coefficient and the activity of magnesium in a Mg-Zn alloy containing 0.32 atom fraction of magnesium at 727°C (1000 K). 

The excess partial molar free energy of mixing of magnesium can be calculated from its activity coefficient value with the help of the following equation ... 

Exercise Calculate the activity coefficients and the activities of the different ions present in solution after the dissolution of potassium chloride 10 " mol/L and magnesium sulfate 10 " mol/L in water. Both electrolytes are strong. Ions exhibit neither an acidic property nor a basic character. 

Figure 4.3 shows a comparison of the variations of the mean activity coefficient of magnesium chloride as a function of the ionic strength. The points are obtained experimentally and the downward curve is obtained by application of Debye and HiickeTs law. The figure demonstrates that the model begins to deviate from the experimental values long before the ionic strength reaches one. In particular, for most electrolytes, the real curve exhibits an extremum which Debye and Huckel s model never shows. 

Figure 4.3. Variations of the mean activity coefficient of magnesium chloride with the ionic strength...

Fig. 9.1 Shows calculated single ion activity coefficients (y) for the common cations sodium, potassium, magnesium, and calcium as their chloride salts as a function of solution ionic strength...

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