Rubidium and caesium

In natural waters rubidium and caesium ions occur at the most in traces. Either flame photometry (method 3.3.. 1) or A AS (method 3.3.4.2) following concentration by coprecipitation with potassium as tetraphenylborate is recommended for the quantitative determination of rubidium and caesium ions in water or for their semi-quantitative estimation (in the case of caesium, AAS-method 3.3 A A and method with concentration 3.3.4.5). 

Potassium, rubidium and caesium ions together with tetraphenylborate ions form a precipitate which does not dissolve readily in water. According to W. Geilmann and W. Gebauhr the solubility products are  

For concentration, the rubidium and caesium ions are precipitated in the form of tetraphenylborates together with potassium ions, which serve as carriers. The lower solubility of the rubidium and caesium tetraphenylborates (see the solubility products) compared with the potassium salt means that under the selected precipitation conditions the rubidium and caesium yields are virtually quantitative. 

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The alkali metals form a homogeneous group of extremely reactive elements which illustrate well the similarities and trends to be expected from the periodic classification, as discussed in Chapter 2. Their physical and chemical properties are readily interpreted in terms of their simple electronic configuration, ns, and for this reason they have been extensively studied by the full range of experimental and theoretical techniques. Compounds of sodium and potassium have been known from ancient times and both elements are essential for animal life. They are also major items of trade, commerce and chemical industry. Lithium was first recognized as a separate element at the beginning of the nineteenth eentury but did not assume major industrial importance until about 40 y ago. Rubidium and caesium are of considerable academic interest but so far have few industrial applications. Francium, the elusive element 87, has only fleeting existence in nature due to its very short radioactive half-life, and this delayed its discovery until 1939. 

In addition to the above oxides M2O, M2O2, M4O6, MO2 and MO3 in which the alkali metal has the constant oxidation state 4-1, rubidium and caesium also form suboxides in which the formal oxidation state of the metal is considerably lower. Some of these intriguing compounds have been known since the turn of the century but only recently have their structures been elucidated by single crystal X-ray analysis. Partial oxidation of Rb at low temperatures gives RbeO which decomposes above —7.3°C to give copper-coloured metallic crystals of Rb902 ... 

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,... 

F. M. Perel inan, Rubidium and Caesium, Pergamon Press, Oxford, 1965. 

The development of chemistry itself has progressed significantly by analytical findings over several centuries. Fundamental knowledge of general chemistry is based on analytical studies, the laws of simple and multiple proportions as well as the law of mass action. Most of the chemical elements have been discovered by the application of analytical chemistry, at first by means of chemical methods, but in the last 150 years mainly by physical methods. Especially spectacular were the spectroscopic discoveries of rubidium and caesium by Bunsen and Kirchhoff, indium by Reich and Richter, helium by Janssen, Lockyer, and Frankland, and rhenium by Noddack and Tacke. Also, nuclear fission became evident as Hahn and Strassmann carefully analyzed the products of neutron-bombarded uranium. 

Sodium silicide ignites in air [1], and like its potassium, rubidium and caesium analogues, ignites explosively on contact with water or dilute acids [2],... 

Reactivity towards air or oxygen increases from lithium to caesium, and the intensity depends on state of subdivision and on presence or absence of moisture. Lithium normally ignites in air above its m.p., while potassium may ignite after exposure to atmosphere, unless it is unusually dry. Rubidium and caesium ignite immediately on exposure [1], It is reported that sodium and potassium may be distilled unchanged under perfectly dried oxygen [2],... 

Sodium hydride ignites in oxygen at 230°C, and finely divided uranium hydride ignites on contact. Lithium hydride, sodium hydride and potassium hydride react slowly in dry air, while rubidium and caesium hydrides ignite. Reaction is accelerated in moist air, and even finely divided lithium hydride ignites then [1], Finely divided magnesium hydride, prepared by pyrolysis, ignites immediately in air [2], See also COMPLEX HYDRIDES... 

Monorubium acetylide and monocaesium acetylide incandesce with warm phosphorus. Lithium acetylide and sodium acetylide bum vigorously in phosphorus vapour, and the potassium, rubidium and caesium analogues should react with increasing violence. 

Shen and Li [149] extracted rubidium (and caesium) from brine samples with 4-ferf-butyl-2-(o -methyl-benzyl) phenol prior to atomic absorption determination of the metal. 

FABMS has been used as a semiquantitative indication of the selectivity of receptors for particular guest metal cations (Johnstone and Rose, 1983). The FABMS competition experiment on [7] with equimolar amounts of the nitrates of sodium, potassium, rubidium and caesium gave gas-phase complex ions of ([7] + K)+ ion (m/z 809) and a minor peak ([7] + Rb)+ ion (m/z 855) exclusively. The relative peak intensities therefore suggested a selectivity order of K+ Rb+ Na+, Cs+, indicative of the bis-crown effect, the ability of bis-crown ether ligands to complex a metal cation of size larger than the cavity of a single crown ether unit, forming a sandwich structure. 

The collected papers of a symposium at Dallas, April 1956, cover all aspects of the handling, use and hazards of lithium, sodium, potassium, their alloys, oxides and hydrides, in 19 chapters [1], Interaction of all 5 alkali metals with water under various circumstances has been discussed comparatively [2], In a monograph covering properties, preparation, handling and applications of the enhanced reactivity of metals dispersed finely in hydrocarbon diluents, the hazardous nature of potassium dispersions, and especially of rubidium and caesium dispersions is stressed [3], Alkaline-earth metal dispersions are of relatively low hazard. Safety practices for small-scale storage, handling, heating and reactions of lithium potassium and sodium with water are reviewed [4],... 

The metal fulminates are all powerfully explosive. Of several salts examined, those of cadmium, copper and silver were more powerful detonators than mercury fulminate, while thallium fulminate was much more sensitive to heating and impact. Formally related salts are also explosive [1]. Sodium, potassium, rubidium and caesium fulminates are all easily detonated by feeble friction or heat. They all form double salts with mercury(II) fulminate which also explode readily, that of the rubidium salt at 45 °C [2],... 

Potassium, rubidium and caesium tetrafluorochlorates and hexafluorobromates react violently with water, and explosively with common organic solvents, like the parent halogen fluorides [1], Silver and barium tetrafluorobromates ignite in contact with ether, acetone, dioxane and petrol [2], Individual entries are ... 

A remarkable property of the atomic weights was discovered, in the sixties, independently by Lothar Meyer and Mendeleeff. They found that the elements could be arranged in rows in the order of their atomic weights so that similar elements would be found in the same columns. A modernised form of the Periodic Table will be found on pp. 106, 107. It will be noticed, for example, that the "alkali" metals, Lithium, Sodium, Rubidium and Caesium, which... 

Heats of solution, hydration energies and lattice energies are discussed in reference (77). For oxygen and nitrogen donor atoms, only a few compounds of potassium, rubidium, and caesium are known, but several have been characterised for the smaller cations, sodium and lithium. 

Cheary, R. W. 1987. A structural analysis of potassium, rubidium and caesium substitution in barium hollandite. Acta Crystallographica, B43, 28-34. 

Exotic Salts of Lithium, Rubidium and Caesium and their Formulations... 

The electrical conductivities of soln. of a great many compounds in liquid hydrogen halides have been measured by E. H. Archibald and D. McIntosh. The conductivity is raised considerably by phosphoryl chloride. Sodium sodium sulphide, borate, phosphate, nitrate, thiosulphate, and arsenate chromic anhydride potassium nitrate, hydroxide, chromate, sulphide, bisulphate, and ferro- and ferri- cyanide ammonium fluoride and carbonate j rubidium and caesium chloride magnesium sulphate calcium fluoride ... 

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

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