COLLECTION
A
Notes on Qualitative Analysis EDITOR'S NOT=: The following papers have been collected over a period of months. Sin~ilar collections have appeared in previous August issues (3. CHEM.EDUC.,35, 401 (1958); 36, 379 (1959); 37, 407 (1960); 38, 406 (1961); 39,395 (1962);40,413 (1963); and41,435 (1964)). I t is the Editor's hope that collection into one place will prove more attractive to readers than the more frequently used editorial procedure of scattering items such as these through the pages of several issues. We apologize to authors who thus have had to wait to see their work in print. We commend to readers' attention the fact that often these represent thesolution of problems given to freshman students in qualitative analysis courses. We hope thst publication in these pages can stimulate just such activity. If readers merely incorporate these idem into their own laboratory instructions, our battle is only half won. If, beyond that, these ideas suggest t o the readers thst they use their own ingenuity in similar fashion, we are gratified.
Robert A. Edge and Gerald W. A. Fowles The University
Southhampton, England
Applications of Sodium-Lead Alloy in Qualitative Inorganic Analysis
The applications of sodium-lead alloy to the quantitative reduction of Ti(IV), V(V), Cr(III), Mo(VI), W(VI), U(VI), and Fe(II1) in mineral acid have been reported recent,ly.' This note describes how sodium-lead alloy may be used is1 qualitative inorganic analysis, both as a reductant in acid and alkaline media, and as a source of sodium hydroxide for hydroxide precipitations. Reactions were carried out on hoth a macro aud sernimicro scale; reagent grade chemicalsZ were used throughout. The alloy reacts vigorously hut nonviolently with water; 1 g of alloy produces 0.17 g of sodium hydroxide. It is, therefore, especially useful for carrying out reductions in alkaline solution. Reductions in Alkaline Solution
Nitrates, nitrites, and chlorates. Na-Pb alloy can be used with advantage instead of A1 or Zn with alkaline solutions. Nitrates and nitrites yield ammonia, and chlorates give chloride. Chromates and dichromates are hoth reduced by the alloy to give a green solution of sodium chromite(II1) and a bluish-green precipitate of chromium(II1) hydroxide. Permanganates are reduced to give emerald green manganate(V1) solutions which are subsequently reduced to brown manganese(II1) hydroxide. Selenates, selenites, tellurates, and tellurites were reduced to the appropriate elemental state. Arsenic and antimony compounds. Aqueous solutions of these elements in their ter- or quinquevalent states yielded the appropriate hydride (MH3) together with elemental arsenic or antimony. (Blank tests showed that no arsine or stibine were produced when the alloy reacted with water.) The above proredure, unlike Fleitmann's test (reduction with A1 in NaOH 436
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Journal of Chemical Education
solution) does not distiuguish between arsenic and antimony compounds. Reductions in Acid Solution
Persulfates, sulfites, thiosulfates, thiocyanates, phosphites, and hypophosphites. Na-Pb alloy may be used in place of Zn for reduction of these compounds. In cold dilute HC1, persolfates are reduced t,o sulfates and sulfites; and thiosulfates and t,hiocyanates arc reduced to hydrogen sulfide. I n cold dilut'e HtSOn, chlorates are reduced to chlorides, and phospbites and hypophosphites are reduced to phosphine. Chromates and dichro~natesin hot. dilute HzSOp or HC1 are reduced by the alloy to green chromium(1II) and subsequently to blue chromium(I1). Permanganates in warm dilute HzSO~ are reduced to colorless solutions of manganese(I1). Compounds of Ag(I), Hg(II), Bi(III), Cu(II), As(III), As(V), SbiIII), Sb(V), Sn(II,) Sn(IV), AuiIII), Pt(IV), Se(IV), Se(VI), Te(IV), and Te(VI). NaPb alloy displaced Ag, Hg, Bi, Cu, As, Sb, Sn, Au, Pt, Se, and Te from dilute H2S04~olutionsof their compounds in the above-mentioned oxidation states; Hg was also deposit,ed from dilute HNOI solutions of Hg(1) compounds. Some stibine and arsine were evolved during the reduction of t,he arsenic and antimony compounds, respectively, and some hydrogen selenide and telluride were formed in reductions of selenium and tellurium solutions. Blank tests using the alloy and dilute HzS04produced trace quantihies only of arsine and stibine. 'EDGE. R.. A.. 191 (1965).
AND
FOWLES. G. W. A,. Anal. Chim. Ada. 32.
2 Sodium-lead alloy (10% Na) was supplied by British Drug Houses Ltd.
