Rubidium solubilities

Rubidium metal alloys with the other alkaU metals, the alkaline-earth metals, antimony, bismuth, gold, and mercury. Rubidium forms double haUde salts with antimony, bismuth, cadmium, cobalt, copper, iron, lead, manganese, mercury, nickel, thorium, and 2iac. These complexes are generally water iasoluble and not hygroscopic. The soluble mbidium compounds are acetate, bromide, carbonate, chloride, chromate, fluoride, formate, hydroxide, iodide. 

Rubidium bromide [7789-39-1 ] M 165.4, m 682°, b 1340°, d 3.35. A white crystalline powder which crystallises from H2O (solubility. 50% in cold and 67% in boiling H2O to give a neutral soln). Also crystd from near-boiling water (0.5mL/g) by cooling to 0°. 

I. Sodium tetraphenylborate Na+ [B(C6H5)4] . This is a useful reagent for potassium the solubility product of the potassium salt is 2.25 x 10 8. Precipitation is usually effected at pH 2 or at pH 6.5 in the presence of EDTA. Rubidium and caesium interfere ammonium ion forms a slightly soluble salt and can be removed by ignition mercury(II) interferes in acid solution but does not do so at pH 6.5 in the presence of EDTA. 

Ammonium may be determined by predpitation with sodium tetraphenylborate as the sparingly soluble ammonium tetraphenylborate NH4[B(C6H5)4], using a similar procedure to that described for potassium it is dried at 100°C, For further details of the reagent, including interferences, notably potassium, rubidium, and caesium, see Section 11.38,... 

All hydroxides (except lithium, sodium, potassium, cesium, rubidium, and ammonia) are insoluble Ba(OH)2 is moderately soluble Ca(OH)2 and Sr(OH)2 are slightly soluble. 

Conventional preparation is, however, nearly useless for microanalysis of soluble elements as it leads to major loss from and redistribution within the tissue. For example, it has been conclusively shown that a very high percentage (over 80%) of rubidium (as an analogue for potassium) is lost from labeled leaf tissues during conventional preparation... 

As shown in Table 11.1, hydrothermal emissions are a major source of soluble iron, manganese, and zinc and a minor source of aluminum, cobalt, copper, and lead. Other elements with significant hydrothermal inputs include lithium, rubidium, cesium, and potassium. Considerable uncertainty also surroimds these flux estimates because they are the result of extrapolations from measurements made at a small number of hydrothermal systems at single points in time. These fluxes appear to vary significantly over short time scales as tectonic activity abruptly opens and closes cracks in the oceanic crust. 

Bromine combines with rubidium and cesium bromides forming solid poly-bromo complexes that can be crystallized from aqueous solutions. The complexes are soluble in liquid bromine. 

Rubidium is recovered from its ore lepidolite or pollucite. Mineral lepidolite is a lithium mica having a composition KRbLi(OH,F)Al2Si30io. The ore is opened by fusion with gypsum (potassium sulfate) or with a mixture of barium sulfate and barium carbonate. The fused mass is extracted with hot water to leach out water-soluble alums of cesium, rubidium, and potassium. The solution is filtered to remove insoluble residues. Alums of alkali metals are separated from solution by fractional crystallization. Solubility of rubidium alum or rubidium aluminum sulfate dodecahydrate, RbAl(S04)2 I2H2O falls between potassium and cesium alum. 

As discussed in the previous section, trace elements are essentially retained in the solid combustion products and, because many are present on the surfaces of the particles, they are potentially leachable. Our data show the elements Mo, As, Cu, Zn, Pb, U, Tl, and Se will be readily accessible for leaching. A significant fraction of the V, Cr, and Ni, and a minor proportion of the Ba and Sr will also be potentially leachable because of the surface association, but most of these elements appear to be located in particles and will be released more slowly as the dissolution of the glass and other phases takes place. Rubidium, Y, Zr, Mn, and Nb are contained almost entirely within the particles and dissolution is potentially slower. The extent to which elements are leached also depends on their speciation and solubility in the porewaters, and the pH exerts a major control. In oxidizing solutions, elements such as, Cd, Cu, Mn, Ni, Pb, and Zn form hydrated cations that adsorb onto mineral surfaces at higher pH values and desorb at lower pH values. In contrast, the elements As, U, Mo, Se, and V, under similar Eh conditions, form oxyanions that adsorb onto mineral surfaces at low pH values and desorb at higher values (Jones 1995). 

Rubidium acid salts are usually prepared from rubidium carbonate or hydroxide and the appropriate acid in aqueous solution, followed by precipitation of the crystals or evaporation to dryness. Rubidium sulfate is also prepared by the addition of a hot solution of barium hydroxide to a boiling solution of rubidium alum until all the aluminum is precipitated. The pH of the solution is 7.6 when the reaction is complete. Aluminum hydroxide and barium sulfate are removed by filtration, and rubidium sulfate is obtained by concentration and crystallization from the filtrate. Rubidium aluminum sulfate dodecahydrate [7488-54-2] (alum), RbA SO 12H20, is formed by sulfuric acid leaching of lepidolite ore. Rubidium alum is more soluble than cesium alum and less soluble than the other alkali alums. Fractional crystallization of Rb alum removes K, Na, and Li values, but concentrates the cesium value. Rubidium hydroxide, RbOH, is prepared by the reaction of rubidium sulfate and barium hydroxide in solution. The insoluble barium sulfate is removed by filtration. The solution of rubidium hydroxide can be evaporated partially in pure nickel or silver containers. Rubidium hydroxide is usually supplied as a 50% aqueous solution. Rubidium carbonate, Rb2C03, is readily formed by bubbling carbon dioxide through a solution of rubidium hydroxide, followed by evaporation to dryness in a fluorocarbon container. Other rubidium compounds can be formed in the laboratory by means of anion-exchange techniques. Table 4 lists some properties of common rubidium compounds. 

E. Muller made potassium iodate by electrolyzing the iodide. H. L. Wheeler 44 made rubidium iodate, RbI03, by the action of a mol. of iodine pentoxide on one of rubidium carbonate by treating a hot dil. soln. of iodine trichloride with rubidium hydroxide or carbonate by the action of iodic acid on a hot cone. soln. of rubidium chloride, RbCl. T. V. Barker obtained a good yield by passing chlorine into a hot cone. soln. of a mixture of rubidium iodide and hydroxide whereby the sparingly soluble iodate is precipitated. Caesium iodate, CsI03, was made in a similar way. 

Sodium iodate dissolves copiously in warm dil. sulphuric acid without decomposition but it is decomposed by hydrochloric acid. The presence of potassium iodide causes potassium iodate to dissolve more readily than in pure water and although A. Ditte says that a double salt is not obtained from the soln., yet the phenomenon is probably due to the formation of a complex salt in soln. J, N. Bronsted measured the solubility of potassium iodate in aq. soln. of potassium hydroxide. Potassium iodate does not dissolve in alcohol. According to H. L. Wheeler, 100 grms. of water at 23° dissolve 21 grms. of rubidium iodate, and 26 grms. of caesium iodate at 24°. The specific gravity of a sat. aq. soln. of lithium iodate 52 at 18° is 1 568 thesp. gr. of soln. of potassium iodate calculated by G. T. Gerlach. from P. Kremers data, are ... 

Fig. 32.—Solubilities of Potassium, Rubidium, and Caesium Perchlorates in Water.

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