Species predominant

These are of two general kinds octahedral, pink complexes and tetrahedral, blue complexes. If cobalt(II) chloride is dissolved in aqueous solution, the predominant species is the hexaaquo-ion [ColHjO) ] (pink). If this solution is heated, it becomes blue, and the same effect is observed if chloride ion is added in excess. This colour change is associated with the change... 

It is found in practice that for a number of compounds reacting ma the predominant species an almost horizontal plot is obtained. For compounds presumed to be nitrated via the free bases, such as 2,6-lutidine i-oxide and 3- and 5-methyl-2-pyridone, slopes of approximately unity are obtained. Since this type of plot allows for the incomplete ionisation of nitric acid, it can be used at higher acidities than plots using — ( H + logio Hjo) which break down when the condition is no longer true. 

For potentials more positive than the standard-state potential, the predominate species is Fe +, whereas Fe + predominates for potentials more negative than E°. When coupled with the step for the Sn +/Sn + half-reaction, we see that Sn + can be used to reduce Fe +. If an excess of Sn + is added, the potential of the resulting solution will be near -1-0.154 V. 

Ladder diagrams provide a simple graphical description of a solution s predominate species as a function of solution conditions. They also provide a convenient way to show the range of solution conditions over which a buffer is most effective. For ex-... 

The extraction efficiency, therefore, is almost 75%. When the same calculation is carried out at a pH of 5.00, the extraction efficiency is 60%, but the extraction efficiency is only 3% at a pH of 7.00. As expected, extraction efficiency is better at more acidic pHs when HA is the predominate species in the aqueous phase. A graph of extraction efficiency versus pH for this system is shown in Figure 7.23. Note that the extraction efficiency is greatest for pHs more acidic than the weak acid s piQ and decreases substantially at pHs more basic than the pi A- A ladder diagram for HA is superimposed on the graph to help illustrate this effect. 

Commercial grades of socbum aluminate contain both waters of hycbation and excess socbum hycboxide. In solution, a high pH retards the reversion of socbum aluminate to insoluble aluminum hycboxide. The chemical identity of the soluble species in socbum aluminate solutions has been the focus of much work (1). Solutions of sodium aluminate appear to be totaby ionic. The aluminate ion is monovalent and the predominant species present is deterrnined by the Na20 concentration. The tetrahydroxyaluminate ion [14485-39-3], Al(OH) 4, exists in lower concentrations of caustic dehydration of Al(OH) 4, to the aluminate ion [20653-98-9], A10 2) is postulated at concentrations of Na20 above 25%. The formation of polymeric aluminate ions similar to the positively charged polymeric ions formed by hydrolysis of aluminum at low pH does not seem to occur. Al(OH) 4 has been identified as the predominant ion in dilute aluminate solutions (2). 

Oceanic residence time, log yr Predominant species Cone, seawater, -log M... 

The Wilkinson hydrogenation cycle shown in Figure 3 (16) was worked out in experiments that included isolation and identification of individual rhodium complexes, measurements of equiUbria of individual steps, deterrnination of rates of individual steps under conditions of stoichiometric reaction with certain reactants missing so that the catalytic cycle could not occur, and deterrnination of rates of the overall catalytic reaction. The cycle demonstrates some generally important points about catalysis the predominant species present in the reacting solution and the only ones that are easily observable by spectroscopic methods, eg, RhCl[P(CgH 2]3> 6 5)312 (olefin), and RhCl2[P(CgH )2]4, are outside the cycle, possibly in virtual equiUbrium with... 

The predominant species observed in SIMS spectra are singly charged atomic and molecular ions [51], However, inorganic and organic cluster ions can also be formed. If the sample consists of a simple single-component metal, then clusters such as M, M, etc., are observed in addition to M+ [52], Oxidation of the metal results in formation of MO ", MO/, M Oll", etc. The relative yield of MO+ to M+ depends on the bond dissociation energy of the oxide [52], For a two-component, oxidized metal, clusters of the type M/", M N, MjO, and M N O/ are observed [51]. 

Still lower pHs to give a pale-yellow solution. As a result of spectrophotometric studies there is general agreement that the predominant species in the initial colourless solution is the tetrahedral V04 ion and, in the final pale-yellow solution, the angular VOz ion. In the intervening orange to red solutions a complicated series of hydrolysis-polymerization reactions occur, which have direct counterparts in the chemistries of Mo and W and to a lesser extent Nb, Ta and Cr. The polymerized species involved are collectively known as isopolymetallates or isopolyanions. The determination of the equilibria involved in their formation, as well as their stoichiometries and structures, has been a confused and disputed area, some aspects of which are by no means settled even now. That this is so is perfectly understandable because ... 

A rate law, to be properly interpreted according to Rule 1, must be written in terms of the predominant species in the reaction medium. 

Because the experiments were done in strongly alkaline solutions, Eq. (6-45) is preferred over Eq. (6-44) in expressing the results, for the rate is expressed in terms of the predominant species. Equation (6-41), which may represent the rate-controlling step, has a rate constant given by 4, = k /Km-... 

In region 2, AH is still largely but not entirely the predominant species. The zeroth-order dependence on the H+ concentration suggests that only water is involved ... 

To summarize the analysis of pH profiles, even complex ones, is not an arcane or difficult art. Systematic analysis in terms of ionic equilibria, predominant species, and the reaction orders with respect to [H+] provides the solution. Kinetically indistinguishable alternatives can never, by definition, be distinguished from the kinetic data contained in the pH profile. Other measurements, including some alluded to earlier and others given in Chapter 10, may, however, allow these distinctions. 

In aqueous solution, water competes effectively with bromide ions for coordination to Cir+ ions. The hexaaquacopper(II) ion is the predominant species in solution. However, in the presence of a large concentration of bromide ions, the solution becomes deep violet. This violet color is due to the presence of the tetrabromocuprate(Il) ions, which are tetrahedral. This process is reversible, and so the solution becomes light blue again on dilution with water, (a) Write the formulas of the two complex ions of copper(II) that form, (b) Is the change in color from violet to blue on dilution expected Explain your reasoning. 

List aU chemical species, both elements and compounds, that are believed to exist at equilibrium. By element we mean the predominant species at standard-state conditions, for example, O2 for oxygen at 1 bar and 298.15 K. 

That HCr04, VO and VO2 are the predominant species under the conditions of Espenson s kinetic study originates from evidence cited by Tong and King, and Rossotti and Rossotti, respectively. No binuclear species are detectable in the Cr(III) product. Vanadium(V) retards the reaction and the full form of the rate law is... 

We have also carried out preliminary experiments in which we have detected the laser desorption of ethylene, cyanogen, methanol, and benzene from the Pt(s)[7(111) x (100)] surface. These spectra are shown in Figure 9. In the experiments involving ethylene, cyanogen, and methanol only neutral species are desorbed. In the case of benzene we observe the molecular parent ion in the absence of the electron beam. We believe that this is due to resonance multiphoton ionization of the benzene by the laser after desorption (resonance multiphoton ionization of benzene is very efficient with 249 nm radiation). These spectra are in marked contrast to the results of SIMS experiments which produce a wide variety of complex metal-adsorbate cluster ions. In the case of ethylene, our experiments were performed at 140 K, and under these conditions ethylene is known to be a molecular x-bonded species on the surface. In SIMS under these conditions the predominant species is CH (15)t but in the laser desorption FTMS experiments neutral ethylene is the principal species detected at low laser power. 

The composition of the leachates does not correspond to the composition of the cement at all (Wilson Batchelor, 1967a,b). The predominant species eluted are the soluble sodium salts of phosphate and fluorides, although sodium is only a minor constituent of the cement. For one example of cement examined, the leachate contained 0-28 % sodium and 0-20% phosphate (expressed as a percentage of the amount of the species contained in the cement). For the major constituents of the glass the figures were 0 07% fluoride, 0 02% Al Oj, 0 01 % SiOj and 0 003% CaO. 

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