Studies of Organic Reagents and Methods
Involving Their Use Precipitation of Bismuth, Zinc, and Vanadium with Salicylaldoxime J O H S F. FL.4GG1 AND N. HOWELL FURMAN Frick Chemical Laboratory, Princeton University, Princeton, S . J .
THIS
quantit'ative experiments in which iiot more than 95 per cent of the bismuth was recovered. Precipitation 1%-ascomplete in all cases in which the pH of the supernatant, liquid was bet'ween 7.2 and 9.5 and that of the filtrate from 7.2 to 9.4. Quantitative recovery of bismuth was demonstrated by weighing the bismuth oxide after precipitation a t pH 7.2, 8.2, 8.8, and 9.5 and by qualitative tests on the filtrate a t pH 8.2, 8.5, 9.0, and 9.1.
paper presents observations upon the precipitation of bismuth with salicylaldoxime and also upon the quantitative estimation of zinc in the form of its monosalicylaldoxime salt. There are included some notes upon the black precipitate that is produced by salicylaldoxime in vanadic acid solutions.
Materials and Apparatus The salicylaldosime used in the precipitation of bismuth and zinc was a preparation obtained from the Eastman Kodak Company. A product recrystallized from benzene-petroleum ether mixture was used in the preparation of the vanadium compound. The solutions of the oxime were made by dissolving 1 gram of the oxime in 5 ml. of alcohol and diluting to 100 ml. Bismuth nitrate of reagent grade containing not more than 1 part per 1000 of nonvolatile impurities mas used in preparing solutions. These were standardized by evaporating measured portions and igniting the residue to bismuth trioxide, which was weighed. The average of four concordant determinations was used. In some of the experiments "specpure" bismuth obtained from Adam Hilger (certified t o contain 99.998 per cent of bismuth) was used. Zinc of k n o m purity and vanadic acid of reagent grade were used in the preparation of solutions. Other reagents-ammoniuni nitrate, acids, alkalies, etc.-were of reagent grade. A Beckman pH meter with glass electrode assembly, frequently tested against carefully prepared standard buffers, vias used for the pH measurements. Recently calibrated weights and volumetric ware were used.
TABLE
I.
I)ETERJIIIU.kTION WITH
Bismuth Present
Gram 0.0009 0,0009 0.0109 0,0109 0.0326 0.0325 0.0551 0,0551
Bismuth Found Gram
0.0009
O F BISMKTH AFTER PRECIPIT.\TION
SALICYLALDOXIUE
Difference
0.0007 0.0108 0.0109 0.0326 0.03%5 0.0550 0.0550 0 Ssl.ir: t i .IISU ccr.:aincd b S';>luti.,r. als c,:itsit.ed
.aiiQ. 0.0
Bismuth Present Gram 0.1094 0.1094 0 OlO9Q 0,0109a 0 0109b 0 ,0109b 0,OOi)Sb
-0 2 -0 1 0 0 0 1 0.0 -0 1 -0 1 0.0009b 0.0; gran: Lf Linr. 3 O i grtin. t f silver.
Bismuth Found Gram 0.1093 0 1092 0 0109 0 0107 0 0111 0 0108 0 0011 0 0010
Difference
Ma. -0.1
-0.2 0.0 -0.2
0.2 -0.1 0.2 0.1
CH.IR;\CTEROF PRECIIJITATE. T1.e prwipitate coagulates and filters well, and appears to be insoluble at still higher pII values than tlioie readily nieasurallc with the gliiss electrode. The eomples steadily loses \veigl:t a t 110" C. icr periods as long as 16 l:ours. Carefully ivaslied samples of the preeipitste were dried to constant w i g h t i n a w m i m tle~iceator; the orgsnic mntter wa; then destroyed with the aid of nitric wid, after nhicli the bismuth v a s wiglied as the trioxide. The average bismuth content of tlie material \vas 57.3 pcr cent. This percentage is close to that iJi t!ic I:ypotlietical subl 57.88 per cent stance (C7FIj02S)BiOH,\vl:icli w d ~ contain of bismuth. The simplest metltorl of (lealing with the precipitate for quantitative work i. t o con\mt it to bimrith trioxide.
Gravimetric Determination of Bismuth It was observed in the course of qualitative studies (2) that if salicylaldoxime was added to a n acidified bismuth solution, followed by sufficient ammonia to make the solut,ion alkaline, a yellow precipitate, obviously different from the common basic salts of bismuth, was obtained. Precipit'ation of the bismuth was quantitative, as revealed by testing the filtrates with hydrogen sulfide. A blank test with 0.1 mg. or less of bismuth proved that salicylaldoxime did not interfere with the formation of bismuth sulfide in either alkaline or acidic solutions.
Recommended Procedure To the solution conr:iining not II.CI:C tii:tn 0.1 qrnin u i III>III irh per 100 nil., 1 grni:i o r :+ninic~nili!ni i i ~ r : ~ t ciz adtlcd, i t ~ I 1 1 1 n by ~~l l j nil. O! t1.e 1 ptxr cent sdic~~1.JJosinnc rengrnt for each 0.1 gr?m i n u t h exprctccl to 11 r e y n r . Tile solution is 1ic.ire 1 t o . allLl ~TII.reJth0ro:l 1'1.t.i. 6 .Y nmmonin is nJcletl iintil a s I.igi~:i= 7 . 2 , n n J preferabl?. t,f 9 t I i irnni >ilvrr or zinc, rcspectiycly. lites, t l x p:.c,cipit:atc i.5 :illonrtl to sertle and i.s collec.ted in .: n.eiSim1 puxehin filter cwcible. .4fter thorough ivnstiing Ivitln 1 .I/ n m i i i o i i i n , the prccipit3te is dried for 30 minutes :It 1103 c'. Ti.en 0.3 yrnm of pure arnnioni.im ttle orginic niattrr nitrate is .iJtlcd t o aid in ilecornpu. T1.c crucible. p k c e d ivitliin 3 k r g y r poi tin crucible, is hcnted gently aiid gi~:tdu:illy until tile org.anit* matter i.5 cleit:uyccl, sild finally at t1.e i:ill tert:l)ei'n: ui'e o f 1 Fisller b:irner, repe;iting t h e
rH RANGEFOR COMPLETEPRECIPITATIOS. A series of tests
was made in n-hich 0.0325 gram of bismuth was present per 100 ml. of the solution which contained 1 gram of ammonium
nitrate, 10 ml. of snlicylaldoxime, and enough nitric acid t o prevent hydrolysis. Each solution was warmed to 50" C., and 6 N ammonia was added until the precipitate barely formed, or until the solution had a distinct yellow color. The solutions were stirred mechanically. Apparently the basic snlt n-liich begins t o form at pH 3.4 is converted more or less completely into the salicylaldoxime complex a t pH 7 or slightly higher. In some cases the bismuth complex was filtered and then converted to bianiuth oxide and weighed.
ignitinn.5 to con-rant ~ v c i g ~ t .
The yellow precipitate appears t o form between pH 6.7 and 7 . 0 ; this point is difficult to determine accurately, since more or less of the white basic salt tends to form a t pH 3.4. The solut'ion turns yellow when the bismuth salicylaldoxime forms. Precipitation is not complete a t p H 6.7 to 6.9, as shown by teste of the filtrate with hydrogen sulfide and by
The results of a few simple determinations as well as of a few separations of bismuth from silver or zinc are given in Table I. Bismuth niay be separated from silver and zinc by tlie .s~lieylnldosimeprccedure. Other possibilitiei that have not been testccl arc tlie separation oi lismritli from cadmium, nickel, or cobalt, since the salicylaldosime compounds of
1 Present address, D e p a r t m e n t of Chemistry, University of Rochester, Iiorhester, S . T.
663
INDUSTRIAL AND ENGINEERING CHEMISTRY
664
these metals are soluble in concentrated ammonia. Attempts were made t o separate bismuth from lead in ammoniacal citrate, tartrate, and acetate solutions. I n the former instances neither metal was precipitated; in the acetate solution both were precipitated although the precipitation of the lead was not quantitative.
Determination of Zinc, Using Salicylaldoxime The first mention of tlie precipitation of zinc with salicylaldoxime appears in Ephraim's paper (1). Pearson (6) indicated the properties of the complex which is precipitated a t a definite p H and concluded that the precipitate is unsuited for the gravimetric determination of zinc. The authors' studies, which were completed prior to the publication of Pearson's paper, reveal the existence of a second compound of the reagent with zinc that has more desirable qualities for quantitative purposes. In solutions of p H 7 to 8 it is possible to obtain the compound Zn(C1H602X)2which contains 19.36 per cent of zinc. This compound has the properties reported by Pearson (6) for the salicylaldoxime salt of zinc. Attempts to weigh zinc in this form give extremely variable results, depending upon time of standing before filtration, etc. The freshly precipitated zinc salicylaldoxime undergoes a significant transformation if allowed to stand on a hot plate or steam bath for 10 minutes in contact with the solution a t 90" to 100" C. The original voluminous precipitate becomes dense and curdy. After filtration and washing the precipitate may be dried for several hours a t 110" C. without loss in weight, although an hour is sufficient for drying. The dense product contained according to analysis 32.50 per cent of zinc. This value corresponds closely to the formula Zn(C7H502N),or 32.61 per cent of zinc. The theoretical factor, 0.3261, was used in the following determinations: Zinc
Present Gram 0.0097 0.0250 0.0303 0.0307 0.0404 0.0470 0.0499 0.0638 0.0741 0.0768
Compound Found Gram 0,0297 0.0767 0.0931 0.0945 0.1241 n 1448 0 1541 0.1961 0 1170 0 2363
Zinc Found
Lrror
Gram
Mg.
0.0 0 0 0.1 0.1 0.1 0.2 0.3 0.1 -0 1 0 3
Experiments with the determination of pII by glass electrode technique showed that the first turbidity due to zinc salicylaldoxime appears in the range p H 6.2 to 6.8 with amounts of zinc ranging from 0.0125 to 0.0250 gram per 100 ml. The precipitate redissolves a t p H 8.8 to 9.4. Pearson (6) reported pH values of 6.5 and 8.5 for these points, but he dealt primarily with tlie compound Zn(C7H602N)2.The precipitation of the monosalicylaldoxime compound iq complete between pH 7 and 8. The procedure was further tested by determining zinc after the removal of copper in acetic acid solutions n-ith salicylaldoxime. The same range of errors was found as for pure zinc solutions. Also in a Bureau of Standards brass containing 27.09 per cent of zinc, the salicylaldoxime method for weighing the zinc gave 26.94, 26.95, 27.10, and 26.99 per cent after removal of the other elements by conventional procedures. Cadmium ion forms a precipitate with salicylaldosime under the same conditions as zinc, but the precipitate is more difficult to filter, and upon continued drying there is an odor of salicylaldoxime, indicating either decomposition or transformation from the di- to the monosalicylaldoxime compound. The weight of precipitate is intermediate between that to be expected if the precipitate were Cd(C;H602S)2or C'dC;HSOJ.
VOL. 12, NO. 11
Precipitation of Vanadic Acid by Salicylaldoxime The qualitative observation of the formation of a black precipitate upon addition of salicylaldoxime to a solution of vanadic acid has been noted ( 2 ) . Relatively few complexes of vanadic acid and organic molecules have been reported. The cupferron precipitate has long been used in analysis (8). hlontequi and Gallego (5) prepared cornpounds of S-hydroxyquinoline and vanadic acid, and a complex of vanadic acid and pyridine has been described by Katzoff and Roseman
(4.
The addition of a 1 per cent salicylaldoxime solution in slight excess to vanadic acid-sulfuric acid solution produces a black precipitate, but the vanadium is not quantitatively removed. From 25 to 50 per cent of the vanadium is precipitated from a solution 0.02 Ar in sulfuric acid; 60 to 7 5 per cent of the vanadium is removed a t acidities from 0.05 to 1.0 S; in 2 iV sulfuric acid solution only 35 per cent of the vanadium is precipitated. The black compound may be dried without decomposition a t 110" C. After drying it is not wetted readily by liquids, but may be dissolved by boiling the liquids. Khile still moist the substance is soluble in ether, alcohol, chloroform, acetone, water, acids, and alkalies. The material was not obtained in crystalline form. The vaiiadium of the compound appears to be in the vanadic state. If a little of the substance is dissolved in diluted sulfuric acid a blue color is produced only upon adding reducing agent>. The compound decomposes explosively a t 195" to 200" C. Carefully washed and dried preparations were analyzed for carbon and hydrogen by the ter hleulen semimicromethod ( d ) , for nitrogen by the Kjeldahl procedure ( 7 ) , and for vanadium gravimetrically as oxide. The following results were obtained: Carbon, yo Hydrogen, 5 Sitrogen, yo Vanadium, 53 Oxygen, by difference,
42.45,42.88,42.6U 3.71, 3.52, 3.64
7 . 2 0 , 7.30, 7 . 0 0 18.40,18.57, 18,48
70
.\v. 42.64
A v 3 . 62 Av. 7.11i 4 v . 18. 48 28 i n
The average values point to a ratio of three salicylaldoxime molecules to two atoms of vanadium, and correspond approximately to the empirical formula : C21H2li\j3OloV2. As little as 0.02 mg. of vanadium as vanadic acid in 15 ml. of solution may be detected by adding salicylaldoxime, then 1 ml. of chloroform, and shaking. The complex is extracted to give an orange color; n i t h larger amounts of vanadium the chloroform layer becomes reddish orange. Ferric iron under these conditions gives a similar test. Molybdenum and chromium do not interfere with this qualitative test for vanadium.
Summary Bismuth may be precipitated quantitatively by salicylaldoxime in solutions of p H 7.2 to 9.4 or higher; silver and zinc are not precipitated with the bismuth a t p H values of 9 or higher. The bismuth compound is not weighable and the compound is therefore ignited to bismuth trioxide before weighing. Zinc is precipitated quantitatively by salicylaldoxime a t pH 7 to 8. The compound Zn(C7H602S)2is converted into ZnC7Hs02Yby heating for 10 minutes a t 90" to 100" C. before filtration. The latter compound is a stable weighing form t o il-hich the theoretical factor 0.3261 may be applied. Cadmium under like conditions is precipitated, but the precipitate appears to be a variable mixture of the monoand disalicylaldoxime compounds and is unsuited for weighing. Vanadic acid is precipitated partially by salicylaldoxime in solutions containing free sulfuric acid. The substance contains salicylaldoxime and vanadium in the ratio 3 molecules to
XOVEMBER 15, 1940
ANALYTICAL EDITION
2 atoms, the approximate formula of the complex being CaiHziKsOicVz.
Literature Cited (1)
(2)
Ephraim, F., Ber., 64B, 1215 (1931). Flagg, J. F., and Furman, K. H., IND.EXG.C H E M . , Anal. Ed., 12,
529 (1940). C3) Katzoff, S.,and Roseman, R., J . Am. Chem. Soc., 58, 1785 (1936). (4) Meulen, H. ter, and Hesslinga. J., “Neue Methoden der or-
(5) (6) (7) (8)
665
ganisch-chemischen Analyse”, Leipzig, Akademische Verlagsgesellschaft, 1927. hlontequi, R., and Gallego, >I., Anales soc. espafi, fis. quim., 32, 134 (1934). Pearson, Th. G., Z. anal. Chem., 112, 179 (1938). Scott, W. W., “Standard Methods of Chemical Analysis”, 5th ed., Vol. I, p. 633, New York, D. \-an Nostrand Co., 1939. Turner, IT.-A,, 4 m .J . Sci., 41, 339 (1916); 42, 109 (1916).
PRESESTED befrjre t h e Division uf I’h:-sical a n d Inorganic Chemistry nt the 99th 1 I e e t i n S nf t h e .inieric:in C h t ~ t u ~ c Su,,icty, al C i n c i n n a t i , Ohiu.
Colorimetric Determination of Phosphate S. R. DI(:Ii>I.iT 4 N D R . H . BR-kI-. Illinois .igricultural Experinierit Station, Urbana, Ill.
A colorimetric method for phosphates is described which employs a molybdatehydrochloric acid solution instead of a molybdate-sulfuric acid solution. This method is not affected by chlorides or by ferric ion up to 15 p. p. m. Fading is less rapid than with most methods. The method is applicable for phosphate determinations in soil fusions, hydrochloric acid extracts of soils, w-ater analyses, oceanographic analyses, plant oxidations in which the sample is taken up in hydrochloric acid, and biological determinations.
‘T
HE reduction of phosphomolybdic acid with stannous
chloride to form a blue solution was first reported by Osmond in 1887 (9). Denighs in 1920 (3) modified the conditions to make the reaction more nearly quant’itative and since that time a large number of further modifications h a r e been published. Although Deniges used hydrochloric acid as well as sulfuric acid in preliminary studies, his final procedure, as well as all modifications that have been suggest’ed subsequently, employs sulfuric acid. However, no reason for t h e nonuse of hydrochloric acid has been published. A review of the literature pert’aining to the determination of phosphates in various substances reveals that a t the present time two methods are in general use-that of Truog and Meyer (13) and that of Kuttner (7, 8 ) as modified by Youngburg ( 6 , 1 4 ) . If the concentration of reagents in the final dilute solution for these two methods is compared (Table I), i t is seen that Youngburg’s modification differs from Truog’s in the relatively much greater quantity of ammonium molybdate i t contains. The three reagents are so interrelated in this determination t h a t the ratios of molybdate to acid and of stannous chloride t o acid perhaps exert a greater influence on the depth of color developed than the actual concentration of any of the three in the final solution. For a given quantity of phosphate the Youngburg method produces a slightly deeper color, and fading is less rapid than with the Truog procedure. Kuttner and Cohen ( 7 ) found that hydrochloric acid in 0.5 N solution caused very rapid fading. Truog and Meyer found that 2 p. p. m. of ferric ion as ferric sulfate decreased the color intensity and caused troublesome greenish tints. Dyer and Wrenshall (5), with the Truog and Meyer method, noticed that the rate of fading increased as phosphate concentration increased. More recently Smith, Dyer, Wrenshall, and DeLong ( 1 1 ) have reported on additional factors n-hich influence color development and rate of fading 51-ith the Truog and Meyer procedure. They found that solutions containing 1.0 p. p. ni. or more of ferric ion prevent nor-
mal color development at a given phosphate concentration. They suggest dilution of the solution !Then feasible, or addition of larger amount,s of stannous chloride. As is evident from their data, an appreciable loss of accuracy resulted when 2 or 3 drops instead of 1 drop of stannous chloride Tvere used. Different concentrations of iron still caused significant differences in color development, so that results obtained by this procedure could not be interpreted unless the ferric-ion concentration of each unknov-n solution was also determined. These norkrrs used ferric chloride as a source of iron, consequently, they could not vary t’he ferric-ion concentration without also varying the chloride-ion concentration. Hence the results which they considered to be due solely to changes in t,he ferric-ion concentration were actually due t o the combined effect of at least two variables. TABLE I. C~OSCESTR.~TIOSOF RE.LGEXTS (Cumparison of Youngbuig and T r u o g and \Ieyrr Methods) Final ConcenFinal Final tration, Concen“a tration, Concentration, Molyhdate. SnCl,, H ~ S O I Ratio 70 Ratio $70 Ratio Youngburg Truog and Aleyer
l.O
