Anions relative numbers

Strategy Once you deduce the formula of the ionic compound, it s all downhill. Remember, though, that you have to show the relative numbers of cations and anions. 

The energy of formation of defects in PbF2 are anion Frenkel defect, 0.69 eV cation Frenkel defect, 4.53 eV Schottky defect, 1.96 eV. (a) What point defects do these consist of (b) What are (approximately) the relative numbers of these defects in a crystal at 300 K (Data from H. Jiang et al., 2000). 

For instance, a difficultly soluble salt ApBq on dissociation provides a relative number ofp cations and q anions. Thus, we have ... 

P5 Formulas for ionic com-I pounds are empirical formulas giving the relative number of cations and anions. Although the formula for sodium chloride is NaCl, molecules of NaCl do not exist under ordinary laboratory conditions. 

The formula (VI-29) is valid for any uni-univalent electrolyte. It is evident from this formula that the sign of the liquid junction potential and also the orientation of the diffusion double layer, in respect to the double layer at the electrodes, depends on the relative magnitude of the anion and cation transference numbers. Should the anion transference number exceed that of cation... 

The relative numbers of cations and anions in a compound depend only on their charges and not on the identities of the ions. 

The relative numbers of cations and anions. For example, a formula of M2X will not allow a close-packed anion lattice and occupancy of all of the octahedral holes by the cations because there are too many cations. The structure must either have the cations in tetrahedral holes, have many vacancies in the anion lattice, or have an anion lattice that is not close-packed. 

So far, we have considered only cases in which a single slightly soluble salt attains equilibrium with its component ions in water. The relative concentrations of the cations and anions in such solutions echo their relative numbers of moles in the original salt. Thus, when AgCl is dissolved, equal numbers of moles of Ag (aq) and Cl (aq) ions result, and when Ag2S04 is dissolved, twice as many moles of Ag (aq) ions as SO aq) are produced. A solubility product relationship such as... 

Relative numbers of cations and anions are chosen to achieve electrical neutrality, using the smallest possible integers as subscripts. 

In an ionic crystal the structure adopted represents the most efficient packing of ions of opposite charge subject to the additional influence of thermal energy. Electrostatic forces are non-directional and the structure adopted is determined by three main controls (i) the relative numbers of cations and anions, (ii) the relative sizes of positive and negative ions and (iii) ionic shapes. Additional species, including hydrated or otherwise coordinated ions together with molecules of water... 

The structures of many ionic crystals can be rationalized to a first approximation by considering the relative sizes and relative numbers of the ions present. For monatomic ions, cations are usually smaller than anions (see Appendix 6), although examples such as KF and CsF show that this is... 

To further confirm the effect of the environment around anion exchange groups on the transport numbers of various anions relative to chloride ions, pyridine derivatives, ethyl pyridines (2-, 3- and 4-ethylpyridine) and pyridine methanols (2-, 3- and 4-pyridine methanol) have been reacted with copolymer membranes... 

Besides the effect of the position and identity of the substituent in the pyridinium groups on the transport number between anions, the water contents of the membranes differ according to the nature of pyridine derivatives reacted with the membranes. Figure 5.38 shows the relationship between the transport numbers of various anions relative to chloride ions and water contents of the membranes reacted with ethyl pyridines.103 The permeation of nitrate and bromide ions decreases and that of fluoride ions increases with increasing membrane water content when ethyl pyridines are reacted with the membranes. However, /cis°4 is independent of water content. This might be due to the low mobility of sulfate... 

Effect of Hydrophilic Compounds in Anion Exchange Membranes on Transport Numbers of Various Anions Relative to Chloride Ions... 

Figure 5.49 Change in transport number of various anions relative to chloride ions for the M-2 membrane before and after irradiation. ( ) Before irradiation after irradiation. Electrodialysis of 1 1 various mixed salt solutions (concentration of sodium ion 0.15 moldm 3) was carried out at 3.0mAcm 2 for 60 min using the M-2 membrane without UV irradiation and then after irradiation for 4 h with UV light filtered with a UV-D33S filter.

T. Sata, T. Yamaguchi, K. Kawamura and K. Matsusaki, Transport numbers of various anions relative to chloride ions in modified anion-exchange membranes during electrodialysis, J. Chem. Soc., Faraday Trans., 1997, 93, 457. 

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