Stoichiometry factor

The selectivity here is directly proportional to complex formation constants and can be estimated, once the latter are known. Several methods are now available for determination of the complex formation constants and stoichiometry factors in solvent polymeric membranes, and probably the most elegant one is the so-called sandwich membrane method [31], Two membrane segments of different known compositions are placed into contact, which leads to a concentration polarized sensing membrane, which is measured by means of potentiometry. The power of this method is not limited to complex formation studies, but also allows one to quantify ion pairing, diffusion, and coextraction processes as well as estimation of ionic membrane impurity concentrations. 

Stoichiometry. The effect of bivalent ion occupancy upon the stoichiometry is shown in Figure 1. The stoichiometry factor / is defined as the number of Na+ ions desorbed/M2+ ions adsorbed and the deviation from 2 is a measure of the hydrolytic sodium loss. As before, it appears that NaX is much more sensitive to excess sodium loss than NaY at low occupancy of M2+, the data are comparable with the results of Table II 6-8 ions/unit cell (NaX) and 2.5-3 (NaY), which again differ by a factor of about 2. 

Figure 1. Stoichiometry factor vs. bivalent ion occupancy in NaX (upper curve) and NaY (lower curve) at 25°C for cobalt (squares), nickel (circles), and zinc (triangles) (---------------) confidence interval at 95% level...

Figure 2. Effect of temperature upon stoichiometry factor for adsorption of nickel ions in NaX (circles) and NaY (triangles) , A 25°C O, A 5°C...

Formula (9) for the stoichiometry factor can then be actualized for the TCS chemisorption as ... 

Figure 9.39 Effectiveness, surface coverage and stoichiometry factor for the reaction of silica gel with TCS. Reactions occurred at 623 K for 1 h ( f + ij 6).

The stoichiometry curve can be subdivided into three regions. In the temperature region between 473 K and 673 K, bimolecular and/or secondary reactions are sterically possible. The stoichiometry factor of 1.6, found by Hair49,52 for the reaction of silica, pretreated at 573 K, with methyltrichlorosilane, is reflected in these experiments. Equation (13) proves to be a very useful formula for a relatively fast evaluation of the stoichiometry factor, provided that the initial condition (PS+SS = 1) is fulfilled. The question whether these secondary species originate from bimolecular or secondary reactions, cannot be solved by this curve. 

In the temperature region 673 K - 873 K, the silanols are too far separated to be involved in secondary or bimolecular reactions. In this region the stoichiometry factor is obviously 1. 

It is important to note, that in both cases, the stoichiometry factor no longer has a physical meaning, since it is no longer a reflection of the amount of primary and secondary species on the silica surface (PS + SS is no longer 1). 

One would expect that a reaction with TCS at 623 K also would cause exclusively primary species, originating from either the main reaction (L) or the side reaction (N). Inspection of the NMR spectrum in figure 9.41 (b) shows that all silanols have disappeared. There is no band in the -100 ppm region, and this is consistent with the earlier calculated effectiveness factor of 1. The main feature still is the -36 ppm band, attributed to the primary species. However, a significant band is situated at -60 ppm, indicative for secondary species. The conclusion, based of the stoichiometry factor /, that no secondary species exist on a silica surface pretreated at 973 K, is therefore not entirely correct. Obviously, the bifunctional reaction (O) is highly improbable, so secondary reactions (M) must occur. This is only possible when a certain mobility of the surface species exists on the surface, since -on average- the distance between the surface species is too large to react with each other. 

It was discussed in chapter 9 that trichlorosilylation of silica gel, thermally pretreated at 973 K, and reacted with trichlorosilane at 623 K for 1 h, has a stoichiometry factor (/) of 1.25, which means that about 30% of the chlorosilyl species are secondary and 70% are primary ones. In analogy with the equations of that paragraph, the amount of trichlorosilane (ASi) that has reacted can be calculated, if the increment of Cl groups and the stoichiometry factor are known ... 

However, unless the stoichiometry factors and v, respectively, are identically both equal to one, these numbers of moles are NOT identical. They can be equated if the expressions are modified by the respective stoichiometry factors and as ... 

The Calculation of Chemical Stoichiometry Factors -Worked Examples... 

In order to calculate the stoichiometry factors, and Vg, for a general reaction v A + Vg.B it is necessary to use the Working Method of Table 4.7. Using this Working Method (Table 4.7), this identifies the number of reactive species, the reactants A and B,... 

Table 4.7 A Working Method to determine the stoichiometry factors Vg...

VolCal2 Limiting Reactions - Calculation of Stoichiometry Factors - Working Method - Volumetric Calculations. 

Chapter 1, Moles and Molarity , includes a discussion of volumetric calculations, based on supplied stoichiometry factors for equations, including limiting reagents. It is included as a first chapter to get students without any previous knowledge of chemistry started on a practical course for volumetric chemistry that usually accompanies an introductory inorganic lecture course. 

Chapter 4 describes how the Chemical Properties of the Elements are related to their valence shell configuration, i.e. characteristic or group oxidation number, variable valence, ionic and covalent bonding. This chapter includes a section on the volumetric calculations used in an introductory inorganic practical course, including the calculation of the stoichiometry factors for chemical reactions. 

S per Cu adsorbed, almost pH independent In the presence of chlorides tlic proton stoichiometry factor is lower and increases when pH increases... 

As a check for the correct application of the stoichiometry factors, we multiply the second equation by two, and third by three, and obtain after summing... 

It is not always necessary to use equivalent weights to calculate equivalents. We can also use a stoichiometry factor, n (units of eq/mol), to convert between moles and equivalents. Thus,... 

The equation used to calculate the non-stoichiometry factor, 6, in the general case is ... 

Flo. 7. Stoichiometry factors Z for various proteins in a highly denaturing mobile phase (formic acid/propanol/water) and reversed-pham HPLC. From Geng and Regnier (45). (a) Plots of log k versus log l/f>, (b) Z versus solute molecular weight. 

We see that the Gibbs free energy logarithmically increases with species concentration. The number of moles m (stoichiometry factor in the reaction) appears as an exponent under the logarithm sign. 

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