Separation of Lithium from Magnesium, Sodium, and Potassium Wolfgang Werner lnstitut fur Pharmazeutische Chemie der Westf. Wilhelms-Universitat. Hittorfstr. 58-62, D4400 Munster, Federal Republic of Germany In the course of the classical qualitative inorganic analysis, the cations of magnesium, lithium, sodium, and pokwium art. collec~edas chlorides after expulsion of the ammunium salts. Lithium gives the precipitation reactions of both sodium and magnesium, so it has to he separated beforehand. 'l'u achieve this it was proposed to extract lithium rhloridc, with nmyl alcohol t'rorn the dried solid chlorides mixture ( l a , 2a1. For laver is shaken with an the detection of lithium. the organic " alkaline solution of sodium phosphate to give a white precipitate in the aqueous phase (Zb). Examination of the reason for frequent errors in the analysis of lithium and magnesium by students revealed that not only are both lithium and magnesium chlorides soluble in amyl alcohol hut they also form sparingly soluble white precipitates with alkaline solution of sodium phosphate, which cannot he distinguished directly. The detection of magnesium by treating its cation solution in amyl alcohol with magneson I1 ( l b ,Zc, 30) is selective in the presence of lithium. The blue lake remains in the aqueous phase. Excess magneson I1 is extracted in the organic layer. In the absence of magnesium the aqueous layer becomes colorless. The best method for detectine lithium is flame soectroscopy. The method, however, sufkrs from the fact t h k it will show the corresponding line if traces are present as an impurity and it will be affected by the anions present. The sensitive detection bv iron Deriodate reaeent (Ic. . . 3b). is onlv -Dossible . in the absence of magnesium because magnesium hydroxide interferes. The literature gives several methods for the separation of magnesium before its detection when i t is present in admixture with lithium, sodium, and potassium. If it is precipitated as oxinate (3c) the excess of reagent must he destroyed by oxidation ( I d ) .On the other hand, separation as magnesium hydroxide hy mercuric oxide ( l e ) is not reliable (Zd). Also excess mercuric oxide is eliminated through heating to decompose it and evaporation of the mercury produced. The
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Journal of Chemical Education
formation of insoluble (MgO),(Mg(NO&), by evaporation with nitric acid (4) is again not reliable. Besides the prohlems already mentioned, the fact that the magnesium has been separated from the mixture does not eliminate the problem of lithium interference in the detection of sodium. The detection of notassium is not affected bv.the Dresence . of lithium, sodium, and magnesium. Since the available methods for the detection of maenesium. lithium, and sodium are inadequate onlv in the presenre of lithium, the sevarotion of lithium seems to be the kev to the ~ c c o ; d i n ~ al ~selective , solvent for lithium &loride is to he soueht. I have fo&d that only lithium chloride is extracted by a mixture of one part n- or isoamyl alcohol with 2 to 5 parts of diethyl ether (vlv) saturated with water from the solid mixture of magnesium, lithium, sodium, and potassium chlorides. n-Butanol can also he employed as the alcohol in this mixture. Unsuitable for the -purpose are alcohols that are miscible with water. n-Hexan-1-01 and cyclohexanol were disqualified due to the rather difficult separation of the phases. It was also found that lithium chloride is difficultly soluble in mixtures containing 2-methvlhutan-2-01, For k e final detection of lithium the aforementioned oreanic ohase can he aeitated with the verv sensitive iron veriodatereagent. hisk kill give a white precipitate in the aqueous layer. Literature Clted (1) Jandsr, O . , d Blsaius, E., "Lehrbuehder andykisehen und przparstiven anorganirhe" Chemie," 12thed., Hirzel Verlag, Stuttgarl 1983, a) p. 2M, b) p.436, cl p. 244, d ) p. 435, e J p. 246. (2) Werner, W.. "Qualitative snoqsniache Ansly* fin Phsrmszeuten," Thieme Verlag, Stutwart, 1980.a) pp. 109,117,and231, U p . LO9,clp. 106,dJpp.105and 116. 131 . . Svehh O.."Vod's Textbook of M a u o and SemimicmQditative Inoreanic Analuais." 5B .d..~on&an, London and New York, 1979,s) p:289 bl p. 5 4 7 . 2 p. 493. I11 Kolditz. L.. (Editorl. "Anoreanikum." 6th ed.. VER Deutscher Verlae der Wissen-
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