Potassium halides solubility

The resultant mixture can be separated by fractional crystallization as the trans-isomer is more soluble the m-isomer can be resolved into its enantiomers using optically active anions like a-bromocamphor 7r-sulphonate. These chlorides can be converted into the bromide or iodide complex by refluxing with a solution of the appropriate potassium halide. 

I 5.89 Account for the observation that solubility in water i,-. uerallv increases from chloride to iodide for ionic halides v, h low covalent character (such as the potassium halides)... 

J6 The ammonium km is about the same size (r+ = 151 pm) as the potassium ion ir. 152 pm) and this is a usef ul fact to remember when explaining the resemblance in properties between these two tuns. For example, (he solubilities of ammonium salts arc similar to those of potassium sails. Explain the relation between ionic radius and soloWiiy. On the other hand, all of the potassium halides crystallize in the NaClstrocture with C.N. = 6 (see Chapter 4). but none of the ammonium halides does so. The coordination numbers of the ammonium halides are either four or eight- Suggest an explanation. 

The derivative chemistry of 3-5 has not been further investigated, although the potassium salt may have some advantages in reactions with transition metal halides because of the low solubility of the potassium halide by-products which could facilitate their separation. 

Papers devoted to the studies of metal-oxide solubilities in molten potassium halides are few. In particular, Guyseva and Khokhlov reported the determination of the solubility product of MgO in molten KC1 in the 1067-1195 K temperature range [374], The study was performed by the potentiometric method using the Pt(02) gas-oxygen electrode. The experimental method consisted of the addition of a known quantity of MgCl2 to the pure melt, and measurements of e.m.f. for the following cell ... 

From the above-mentioned studies [374, 375] it can be concluded that, up to now, systematic solubility investigations in molten potassium halides have not been performed. This also concerns other alkali-metal halide melts, although these results would be very useful for the estimation of the effect of melt acidity and anion composition on metal-oxide solubilities at 800 °C. 

We have also investigated the solubilities of MgO and CaO in molten potassium halides at 800 °C [197] to elucidate the effect of anion composition of the halide melt on metal-oxide solubility. The MgO was found to be practically insoluble in chloride and bromide melts, and the iodide-melt could not be investigated owing to intense iodine evolution from strongly acidic solutions. In contrast, CaO solubility products were determined successfully in all the potassium halide melts at 800 °C, by the potentiometric titration method. The corresponding potentiometric titration curves are shown in Fig. 3.7.16. 

The obtained solubility data are presented in Table 3.7.19. The oxide-solubility changes in molten potassium halides can be explained successfully in the framework of the HSAB concept. Indeed, Ca2+ ion belongs to the hard acids, whereas chloride ion is a hard base, bromide ion is an intermediate base and iodide ion is a soft base. Therefore, the stability of calcium hahde complexes should reduce in the chloride-bromide-iodide sequence. Since an increase in the halide complex s stability results in the elevation of the oxide solubility in the melts, one should expect a reduction in the solubility of... 

The solubility of ionic substances in relatively nonpolar aprotic solvents can be greatly enhanced by using catalytic quantities of macrocyclic polyethers, such as 18-crown-6, the structure of which is shown in Fig. 5.5. These macrocyclic ethers selectively solvate the cation, both enhancing solubility and also leaving the anion in a very weakly solvated state. The anions behave under these conditions as highly reactive species, sometimes termed naked anions. A study of the relative rates of nucleophilic substitution on benzyl tosylate by potassium salts in acetonitrile in the presence of 18-crown-6 revealed a pronounced leveling effect. " All the potassium halides (fluoride, chloride, bromide, and iodide) were approximately equal in their reactivity. Potassium acetate was observed to be almost ten times more reactive than potassium iodide under these conditions—a reversal of the normal reactivity of acetate ion versus iodide ion in nucleophilic substitution reactions. As measured by cHji values in Table 5.5, iodide is 3 log units, i.e., 10 times, more reactive than acetate ion in the protic solvent methanol. 

On the contrary, CaO solubility products were successfully determined in all potassium halide melts at 800°C by the potentiometric titration method. 

Silver chloride is readily soluble in ammonia, the bromide less readily and the iodide only slightly, forming the complex cation [Ag(NH3)2]. These halides also dissolve in potassium cyanide, forming the linear complex anion [AglCN) ] and in sodium thiosulphate forming another complex anion, [Ag(S203)2] ... 

Reduction. Hafnium oxide can be reduced using calcium metal to yield a fine, pyrophoric metal powder (see Calciumand calciumalloys). This powder contains considerable oxygen contamination because of oxygen s high solubility in hot hafnium, and caimot be consoHdated into ductile metal. To obtain low oxygen ductile hafnium, the feed must be an oxygen-free halide compound such as hafnium tetrachloride or potassium hexafluorohafnate [16871-86-6]. 

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... 

Iodides can also be determined by this method, and in this case too there is no need to filter off the silver halide, since silver iodide is very much less soluble than silver thiocyanate. In this determination the iodide solution must be very dilute in order to reduce adsorption effects. The dilute iodide solution (ca 300 mL), acidified with dilute nitric acid, is treated very slowly and with vigorous stirring or shaking with standard 0.1 M silver nitrate until the yellow precipitate coagulates and the supernatant liquid appears colourless. Silver nitrate is then present in excess. One millilitre of iron(III) indicator solution is added, and the residual silver nitrate is titrated with standard 0.1M ammonium or potassium thiocyanate. 

Catalytic elfects on the thermal decomposition and burning under nitrogen of the nitrate were determined for ammonium dichromate, potassium dichromate, potassium chromate, barium chloride, sodium chloride and potassium nitrate. Chromium(VI) salts are most effective in decomposition, and the halides salts during burning of the nitrate [1]. The effect of chromium compounds soluble in the molten nitrate, all of which promote decomposition of the latter, was studied (especially using ammonium dichromate) in kinetic experiments [2],... 

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