Electroneutrality

The principle of electroneutrality in aqueous chemical systems states that the sum of the concentrations of all positively charged ions (expressed in equivalents) equals the sum of the concentrations of all negatively charged ions, so that the overall charge of the solution is zero. (If this were not true, we would be constantly bombarded with electrical shocks ) When an equation based on the principle of electroneutrality is combined with equations provided by conservation of mass, and by the mass action law, Eq. [1-12], the equilibrium chemical composition of a system can be calculated. 

A water sample is taken from a stream in Nevada receiving acid mine drainage. The stream passes through an area containing gypsum, CaS04. Laboratory analysis shows that the pH of the water is 4, the total concentration of sulfate (SO2-) is 6 X 10-3 M, and the total concentration of chloride (CL) is 3 X 10-4 M. (a) Assuming that the only other ionic species present is calcium (Ca2+), what is the calcium concentration in the water (b) Will the precipitation reaction, 

Because the reaction quotient 1044 is less than the equilibrium constant 1 O 1 2, the reaction will proceed to the right and a solid should form the extent to which a solid actually forms may be limited by kinetic considerations. 

In 1948 Pauling proposed the powerful electroneutrality principle. This says that the atoms in molecules arrange themselves so that their net charges fall within rather narrow limits, from about +1 to —1 overall. In fact, the range fw any 

We also alter the orbital energies as we go from left to right in the transition series. For each step to the right, a proton is added to the nucleus. This extra positive charge stabilizes all the orbitals. The earlier metals are more electropositive because it is easier to remove electrons from their less stable energy levels. The 

Nature seems to strongly discourage any process that would lead to an excess of positive or negative charge in matter. Suppose, for example, that we immerse a piece of zinc metal in pure water. A small number of zinc atoms go into solution as Zn ions, leaving their electrons behind in the metal  

As this process goes on, the electrons which remain in the zinc cause a negative charge to build up within the metal which makes it increasingly difficult for additional positive ions to leave the metallic phase. A similar buildup of positive charge in the liquid phase adds to this inhibition. Very soon, therefore, the process comes to a halt, resulting in a solution in which the concentration of Zn2+ is still too low (around 10-10 M) to be detected by ordinary chemical means. 

The only way we can get the oxidation of the metal to continue is to couple it with some other process that restores electroneutrality to the two phases. A simple way to accomplish this would be to immerse the zinc in a solution of copper sulfate instead of pure water. As you will recall if you have seen this commonly-performed experiment carried out, the zinc metal quickly becomes covered with a black coating of finely-divided metallic copper. The reaction is a simple oxidation-reduction process, a transfer of two electrons from the zinc to the copper  

The dissolution of the zinc is no longer inhibited by a buildup of negative charge in the metal, because the excess electrons are removed from the zinc by copper ions that come into contact with it. At the same time, the solution remains electrically neutral, since for each Zn ion introduced to the solution, one Cu ion is removed. The net reaction 

The d orbitals of transition metals are only fully available for back donation in low oxidation states. Although (f Co(III), for example, does have a filled level, it is unavailable for back bonding—Co(III) therefore cannot bind CO. The high positive charge of Co(in) contracts all the orbitals with the result that the d orbital is low in energy and therefore only weakly basic. Likewise, repulsive effects of it donors such as F and RO are mild. 

There is a sharp difference between d° and d as in Ti(IV) versus Ti(II) d° Ti(IV) cannot back bond at all, while (f Ti(II) is a very strong back-bonder because early in the transition series, where (f states are most common, the d orbitals are relatively unstable for the reasons mentioned earlier. The cf Ti(IV) species (C5Hs)2TiCl2 therefore does 

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The chemical potential pi, has been generalized to the electrochemical potential Hj since we will be dealing with phases whose charge may be varied. The problem that now arises is that one desires to deal with individual ionic species and that these are not independently variable. In the present treatment, the difficulty is handled by regarding the electrons of the metallic phase as the dependent component whose amount varies with the addition or removal of charged components in such a way that electroneutrality is preserved. One then writes, for the ith charged species. 

In the interfacial region, electroneutrality requires that c, = (5 ) + c, so that Eq. XV-4 becomes... 

In general, then, anion-forming adsorbates should find p-type semiconductors (such as NiO) more active than insulating materials and these, in turn, more active than n-type semiconductors (such as ZnO). It is not necessary that the semiconductor type be determined by an excess or deficiency of a native ion impurities, often deliberately added, can play the same role. Thus if Lr ions are present in NiO, in lattice positions, additional Ni ions must also be present to maintain electroneutrality these now compete for electrons with oxygen and reduce the activity toward oxygen adsorption. 

The electroneutrality condition can be expressed in temis of the integral of the charge density by recognizing the obvious fact that the total charge around an ion is equal in magnitude and opposite in sign to the charge on the central ion. This leads to the zeroth moment condition... 

This is called the DHLL+52 approximation. On carrying out the integrations over q y(r) and q iryll and using the electroneutrality condition, this can be rewritten as [63]... 

For a synnnetrical system in which the reference species are identical (e.g. hard spheres of the same size), the integral can be taken outside the summation, which then adds up to zero due to the electroneutrality condition, to yield... 

In principle, the effects of the concentration of ions can be removed by dividing A2.4.31 by the concentration. Taking Avagadro s constant as L and assuming a concentration of solute c mol m, then from the electroneutrality principle we have = A = z cL and clearly... 

Furthemiore, we must have = 0 since the overall solution is electroneutral. Finally we end up with... 

In all cases of localized corrosion, tlie ratio of the catliodic to tlie anodic area plays a major role in tlie localized dissolution rate. A large catliodic area provides high catliodic currents and, due to electroneutrality requirements, tlie small anodic area must provide a high anodic current. Hence, tlie local current density, i.e., local corrosion rate, becomes higher witli a larger catliode/anode-ratio. 

The condensation of aldehydes or ketones with secondary amines leads to "encunines via N-hemiacetals and immonium hydroxides, when the water is removed. In these conjugated systems electron density and nudeophilicity are largely transferred from the nitrogen to the a-carbon atom, and thus enamines are useful electroneutral d -reagents (G.A. Cook, 1969 S.F. Dyke, 1973). A bulky heterocyclic substituent supports regio- and stereoselective reactions. 

The following acid-catalyzed cyclizations leading to steroid hormone precursors exemplify some important facts an acetylenic bond is less nucleophilic than an olelinic bond acetylenic bonds tend to form cyclopentane rather than cyclohexane derivatives, if there is a choice in proton-catalyzed olefin cyclizations the thermodynamically most stable Irons connection of cyclohexane rings is obtained selectively electroneutral nucleophilic agents such as ethylene carbonate can be used to terminate the cationic cyclization process forming stable enol derivatives which can be hydrolyzed to carbonyl compounds without this nucleophile and with trifluoroacetic acid the corresponding enol ester may be obtained (M.B. Gravestock, 1978, A,B P.E. Peterson, 1969). 

The second type of equation is a charge balance equation. A charge balance equation is a statement of solution electroneutrality. 

We consider this system in an osmotic pressure experiment based on a membrane which is permeable to all components except the polymeric ion P that is, solvent molecules, M" , and X can pass through the membrane freely to establish the osmotic equilibrium, and only the polymer is restrained. It does not matter whether pure solvent or a salt solution is introduced across the membrane from the polymer solution or whether the latter initially contains salt or not. At equilibrium both sides of the osmometer contain solvent, M , and X in such proportions as to satisfy the constaints imposed by electroneutrality and equilibrium conditions. 

There are two additional concepts which we can invoke to simplify Eq. (8.118) electroneutrality and a less familiar principle called Donnan equilibrium. Some relationships pertaining to these are developed below ... 

Electroneutrality requires simply that the same amounts of positive and negative charge be present in a solution. Applying this separately to both the a and P phases, we obtain... 

The analysis of oxidation processes to which diffusion control and interfacial equilibrium applied has been analysed by Wagner (1933) who used the Einstein mobility equation as a starting point. To describe the oxidation for example of nickel to the monoxide NiO, consideration must be given to tire respective fluxes of cations, anions and positive holes. These fluxes must be balanced to preserve local electroneutrality tliroughout the growing oxide. The flux equation for each species includes a term due to a chemical potential gradient plus a term due to the elecuic potential gradient... 

In the absence of die polyether, potassium fluoride is insoluble in benzene and unreactive toward alkyl halides. Similar enhancement of solubility and reactivity of other salts is observed in the presence of crown ethers The solubility and reactivity enhancement result because the ionic compound is dissociated to a tightly complexed cation and a naked anion. Figure 4.13 shows the tight coordination that can be achieved with a typical crown ether. The complexed cation, because it is surrounded by the nonpolar crown ether, has high solubility in the nonpolar media. To maintain electroneutrality, the anion is also transported into the solvent. The cation is shielded from interaction with the anion as a... 

Our final focus in this review is on charged quenched-annealed fluid systems. Very recently Bratko, Chakraborty and Chandler have addressed this problem [34-36]. A set of grand canonical computer simulation results for infinitely diluted electrolyte adsorbed in an electroneutral matrix of ions has been presented and an attempt to describe them at the level of... 

The electrolyte solution is modelled as a two-component, electroneutral system of point ions with charges ez, = ezL = ez. The density of the fluid is (p+ = pL = p /2). The fluid-fluid and fluid-matrix Coulomb interactions are... 

It is evident from these results that the interactive properties of the investigated SEC PS/DVB or DVB gels are very different. Because polar electroneutral macromolecules of PMMA were more retained from a nonpolar solvent (toluene) than from polar ones (THF, chloroform), we conclude that the dipol-dipol interactions were operative. Columns No. 1 and No. 2 were very interactive and can be applied successfully to LC techniques that combine exclusion and interaction (adsorption) mechanisms. These emerging techniques are LC at the critical adsorption point (18), the already mentioned LC under limiting conditions of adsorption (15,18), and LC under limiting conditions of desorption (16). In these cases, the adsorptivity of the SEC columns may even be advantageous. In most conventional SEC applications, however, the interactive properties of columns may cause important problems. In any case, interactive properties of SEC columns should be considered when applying the universal calibration, especially for medium polar and polar polymers. It is therefore advisable to check the elution properties of SEC columns before use with the... 

According to the electroneutrality principle for this system, Ch = Ca + Cqh and = Ca + Cqh subtracting these equations gives... 

As each B atom contributes 1 electron to its B-Ht bond and 2 electrons to the framework MOs, the (n + 1) framework bonding MOs are just filled by the 2n electrons from nB atoms and the 2 electrons from the anionic charge. Further, it is possible (conceptually) to remove a BHt group and replace it by 2 electrons to compensate for the 2 electrons contributed by the BHi group to the MOs. Electroneutrality can then be achieved by adding the appropriate number of protons this does not alter the number of electrons in the system and hence all bonding MOs remain just filled. 

Positively charged and electroneutral macroheterocycles as host molecules for anions 97CRV1609. 

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