Aqueous cations

Experiments and calculations both indicate that electron transfer from potassium to water is spontaneous and rapid, whereas electron transfer from silver to water does not occur. In redox terms, potassium oxidizes easily, but silver resists oxidation. Because oxidation involves the loss of electrons, these differences in reactivity of silver and potassium can be traced to how easily each metal loses electrons to become an aqueous cation. One obvious factor is their first ionization energies, which show that it takes much more energy to remove an electron from silver than from potassium 731 kJ/mol for Ag and 419 kJ/mol for K. The other alkali metals with low first ionization energies, Na, Rb, Cs, and Fr, all react violently with water. 

Some electrodes are made of substances that participate in the redox reactions that transfer electrons. These are active electrodes. Other electrodes serve only to supply or accept electrons but are not part of the redox chemistry these are passive electrodes. In Figure 19-7. both metal strips are active electrodes. During the redox reaction, zinc metal dissolves from the anode while copper metal precipitates at the cathode. The reactions that take place at these active electrodes are conversions between the metals contained in the electrodes and their aqueous cations. 

Fig. 2.37. Phase diagram for Ca0-Na20 Si02-(Al203)-H20 system in equilibrium with quartz at 400°C and 400 bars. Plagioclase solid solution can be represented by the albite and anorthite fields, whereas epidote is represented by clinozoisite. Note that the clinozoisite field is adjacent to the anorthite field, suggesting that fluids with high Ca/(H+) might equilibrate with excess anorthite by replacing it with epidote. The location of the albite-anorthite-epidote equilibrium point is a function of epidote and plagioclase composition and depends on the model used for calculation of the thermodynamic properties of aqueous cations (Berndt et al., 1989).

Shock EL, Sassani DC, Willis M, Sverjensky DA (1997) Inorganic species in geologic fluids Correlations among standard molal thermodynamic properties of aqueous cations and hydroxide complexes. Geochim... 

Aqueous cation C and anion A) associated into ion pair C Aj... 

Table 8.14 Standard potentials for various redox couples (aqueous cation-metal element-aqueous anion) arranged in order of decreasing E°. Valnes, expressed in volts, are consistent with standard partial molal Gibbs free energy values listed in table 8.13. valne for snlfur is from Nylen and Wigren (1971).

Fig.1 Formation of aqueous cation from element in its standard state.

The conventional standard entropy of an aqueous cation may be calculated from the change in standard entropy for its formation and the standard entropies of the element and that of dihydrogen, as shown in the following example for the aqueous sodium ion. 

Table 2.13 Standard molar entropies of some main group elements and the conventional standard molar entropies of their aqueous cations at 25 C (in J K 1 mol- )...

The more exact forms of the aqueous cations, with their primary hydration shells, are normally omitted from the diagrams. As is the case with Crvl, which in acid solution exists as the dichromate ion, Cr2072-, the forms of any oxo anions are indicated by their formulae in the diagrams. The diagram for chromium summarizes the following important properties ... 

The purpose of this chapter is to present a brief overview of the geochemistry of mineral surfaces, including their (1) dissolution mechanisms, (2) development of electrical charge when in contact with aqueous solutions, and (3) uptake of aqueous cations and anions, and to discuss some of the factors that control their chemical reactivity, including (1) defect density, (2) cooperative effects among adsorbates,... 

The example discussed above shows the effect of different solid substrates on the adsorption of a single type of aqueous cation [Co(II)]. The uptake vs. pH curves in Figure 7.6 show the differences in uptake behavior as a function of pH for a variety of aqueous cations and anions on one type of substrate - ferric hydroxide particles [5]. Some of the cations included in Figure 7.6(a), like Pb2+ and Cr3+, sorb at low pH values, whereas others, like Zn2+ and Ni2+, do not sorb until higher pH values are reached. At low pH values, metal oxide and hydroxide surfaces tend to... 

The reaction of an aqueous cation, usually a metal ion, with a free element is among the simplest of all redox processes. The products are a different ion and a different element. Iron metal reacts with aqueous copper(II) ion, for example, to give iron(II) ion and copper metal (Figure 4.2) ... 

Table 20.2 lists standard potentials E° for oxidation of first-series transition metals. Note that these potentials are the negative of the corresponding standard reduction potentials (Table 18.1, page 775). Except for copper, all the E° values are positive, which means that the solid metal is oxidized to its aqueous cation more readily than H2 gas is oxidized to H+(aq). 

Electrolysis of dilute sulfuric acid The chlor-alkali industry Tests for aqueous cations... 

Appearance or smell Flame colours Tests for aqueous cations Tests for aqueous anions Tests for gases... 

Dihydropyridine 129 has been shown to catalyze Michael reactions in aqueous cationic micelles of cetyltri-methylammonium bromide (Scheme 34) <2003CL1064>. In the micelles, dihydropyridine 129 ionizes to form an acetophenone enolate salt 130. The highly basic enolate deprotonates the Michael donor which then rapidly reacts with the Michael acceptor. The use of anionic surfactants did not promote Michael reactions, suggesting that the cationic micelles promote the dissociation of salt 130. 

Unlike elements of the 3d series, 4<2 and 5d elements have the little simple aqueous cationic chemistry. The main exceptions are Y3+ and La3+ and Ag+, which forms some soluble salts (AgF, AgN03). The aqua Ag+ ion shows strong class b complexing behaviour, with an affinity for ligands such as NH3,I- and... 

We will now proceed to a discussion of LIS methodologies, uses of lanthanides in complex NMR spectra, quantitative aspects of the LIS method such as testing and separation of shifts, use of pseudo contact shift in molecular structure, and use of aqueous cations and lanthanide complexes in biological systems. 

As seen in Chapters 4 and 5, aqueous cations and anions are formed by the dissolution of metal oxides and acid phosphates. Electrostatic (Coulomb) force attracts the oppositely charged ions to each other and stacks them in periodic configurations. That results in an ionic crystal structure. Thus, the ionic bond is one of the main mechanisms that is responsible for forming the acid-base reaction products. 

Note that the aqueous cations are commonly written without the solvent molecules that accompany them. 

Bodmeier, R. Guo, X. Sarabia, R.E. Skultety, P. The influence of buffer species and strength on diltiazemhcl release from beads coated with aqueous cationic polymeric dispersions, Eudragit RS, RL30D. Pharm. Res. 1996,13 (1), 52-56. 

Figure 30-3 Equilibria in the extraction of an aqueous cation into an immiscible organic solvent containing 8-hydroxyquinoline.

Fig. 9 is a schematic phase diagram of a dilute aqueous cationic surfactant solution showing temperature and concentration effects on its microstructures. When the temperature is lower than the Krafft point [the temperature at which the solubility equals the critical micelle concentration (CMC)], the surfactant is partially in crystal or in gel form in the solution. At temperatures above the Krafft point and concentrations higher than the CMC, spherical micelles form in the surfactant solution. With further increase in concentration and/or on addition of counterions, the micelles form cylindrical rods or threads or worms with entangled thread-like and sometimes branched threadlike structures. 

Such systems can form the thread-like micelles necessary for surfactant solutions to be DR under the shearing conditions in turbulent flows. The thread-like micelles align themselves along the flow direction causing DR of the solution. Details of microstructures DR of aqueous cationic surfactant solutions vary with surfactant chemical structure and concentration, counterion chemical structure and... 

Fig. 9 Schematic phase diagram for dilute aqueous cationic surfactant solutions. (From Ref.l l)...

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