THE DETECTION OF THE TIN GROUP METALS AND THEIR SEPARATION FROM THE COPPER GROUP BY MEANS OF AMMONIUM MONOSULFIDE* LEOLEERMAN. COLLEGE 01. THE CITY OX NEWYORR, NEWYORKCITI
The purpose of this work was to investigate the possibility of using ammonium monosulfide to detect the presence of the tin group metals when mixed with the copper group. Ammonium and sodium fiolysulfde.~ cannot be used because on acidification large amounts of sulfur are precipitated and small amounts of the copper group are introduced into the tin group. Ammonium monosulfide, however, does not h o e these disadvantages. The action of various ammonium monosulfide solutions on the sul@s of the copper and tin group was investigated. The best solution was then tested on various mixtures of metallic ions of the copper and tin groups to see $ i t would detect the presence of the latter and also make a sefiaration of the two groups.
...... Introduction
Ammonium and sodium polysulfides, the usual reagents for separating the sulfides of the copper group from those of the tin group, have some serious defects. On acidification to precipitate the tin group sulfides, a large amount of sulfur is also thrown down. This sulfur often masks the tin group sulfides especially when only a small amount is present. Ammonium polysulfide has the further disadvantage of dissolving small amounts of mercuric and cupric sulfides (1)which would appear on acidification of the reagent and erroneously indicate the presence of metals of the tin group. Sodium polysulfide has another drawback in that it dissolves small amounts of copper and bismuth sulfides and does not dissolve all the mercuric sulfide ( 2 ) . Ammonium monosulfide has not been used since it only partially dissolves the sulfides of trivalent antimony and divalent tin, although it completely takes into solution both sulfides of arsenic as well as those of antimony and tin in their higher state of oxidation. I t has the advantage of not yielding a precipitate of sulfur on acidification and of not dissolving any of the copper group suhides. The ideal reagent would be one which would completely dissolve the sulfides of the tin group and none of the sulfides of the copper group and on acidification only precipitate the tin group sulfides. The fact that ammonium monosulfide has more of the characteristics of the ideal reagent than the other two suggested the possibility of its use. The first step in this investigation consisted in the preparation of various ammonium monosulfide solutions. I n order to find the one most suitable for the separation of the two groups, their action was tested on some of the * The author wishes to express his thanks to Professor L. I. Curtman of the College of the City of New York for his valuable suggestions. 916
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DETECTION 6 P TIN GROUP METALS
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individual sulfides of the metals of the copper and tin groups. The reagent selected was now tested on solutions of varying mixtures of the metal ions of the copper and tin groups to determine not only its effectivenessin separating them but also in detecting the presence of the tin group. Experimental Preparation of Ammonium Monosulfide Solutions and Their Action on
the Individual Sulfides of the Copper and Tin Groups. The sulfides of mercury, lead, copper, arsenic (As+++), antimony (Sb+++), and tin (Sn++) were separately made by taking a calculated quantity of a salt of each metal, dissolving and completely precipitating with HzS. The solution through which H a precipitates were washed with 5% NHHaN03 had been passed and then suspended in a known volume of water giving a definite amount of the metal as its sulfide. For each experiment 20 cc. of the weU-shaken mixture (equal to 200 mg. of metal as its sulfide) were filtered by centrifuging. Different ammonium monosulfide solutions were made by bubbling a rapid stream of HPS through 10 CC. of concentrated NHlOH for varying periods of time (5 sec., 10 sec., 15 sec., 30 sec., 1 min., 2 min., 3 rnin.). The NH,OH was contained in an ordinary 20 X 150-mm. pyrex test tube* and the HxS was delivered through a piece of standard wall glass tubing outside diameter) * reaching to the bottom of the liquid. These various solutions (10 cc.) were now added to the sulfides (200 mg. of metal as its sulfide) prepared above and the well-stirred mixture kept a t 60' for 5 minutes, filtered, and the filtrate carefully acidified with dilute (3 N) HCI (3). The color of the liltrate and precipitate, after acidification, was noted. If any precipitate bad been obtained it was analyzed for the particular metal, the sulfide of which had been used. Table I gives the results of these experiments. TABLE I The Action of Various Ammonium Monosulfide Solutions on Some Copper and Tin Group Sulfides Sulfide (ired
HgS PbS CuS AS& Sb& SnS
Color of Piitrote
Colorless Light yellow Greenish yellow Colorles~ Very light reddish brown Light yellow
Rsrull of Acidij3ing ~ i u m t ~
Tart for Mdnl Ion i n ~ r c c i p ~ o lifr , A ~ Y
Gray turbidity Slight white turbidity m i t e turbidity Yellow ppt. Reddish brown ppt. Yellow ppt.
+ As + Sn
+ Sb
In the experiments using HgS, PbS, and CuS, none of the sulfide apparently dissolved. The turbid solutions obtained using HgS and CuS
* This glassware is the usual kind supplied to students.
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JOURNAL OF CHEMICAL EDUCATION
MAY, 1931
were allowed to stand several hours until they cleared. The former deposited small amounts of a black precipitate while from the latter slightly larger quantities of light brown solid separated. The amount of precipitate obtained in both cases increased as the duration of time of passage of H2S into the NH,OH increased. In the experiments employing A d s the sulfide completely dissolved in every ammonium monosulfide solution used. When the ammonium monosulfide solutions were added to the SbzSaand SnS there was no apparent solution though the SbeS3changed to a reddish brown color. The amount of precipitate obtained on acidifying the filtrate from the Sb& and SnS experiments was greater with solutions of ammonium monosulfide which had H a passed in for a longer time. As a blank test the action of concentrated NHIOH on the sulfides was investigated. I t had no effects on HgS, PbS or CuS; it completely dissolved the As& being reprecipitated on acidification; it apparently had no &ect on Sb2S3and SnS though it was necessary to filter the latter mixture several times in order to get a clear solution; on acidification of the filtrates from the ShnS3 and SnS experiments, a small amount of precipitate was obtained in both cases, orange in the former and yellow colored in the latter case. The above experiments show that it would he necessary to pass H a into the NH,OH for longer periods of time if one sought to dissolve more of the ShzSa and SnS. But this is undesirable as more HgS and CuS are carried through into the tin group. Therefore it was necessary to select such a solution which would dissolve appreciable amounts of Sb& and SnS and yet not carry much HgS and CuS with it. The solution which fulfilled these conditions best was the one made by passing H2S for 15 seconds through the concentrated NH,OH. Action of Ammonium Monosulfide (H2Sfor 15 See.) in Separating the Copper and Tin Groups and Detecting the Latter. Solutions containing known quantities of the metals of the copper and tin groups were prepared, completely precipitated with HzS, washed with 5% NH4N03 solution containing HIS, and then treated with the ammonium monosulfide solution for 5 minutes and filtered. Since experiments in which the mixture was kept at room temperature as compared with those a t 60' gave similar results, the warming was omitted in making the separation. The filtrate was acidified and if any precipitate formed it was analyzed for the metals of the tin group. The results of these experiments are given in Table 11. From the results above it can be seen that 5 mg. of As+++ or Sb+++can be detected in the presence of 100 mg. each of the metals of the copper group. If copper is absent 5 mg. of Sn++ can also be detected but in the presence of 100 mg. of Cu++, 10 mg. Sn++ will give a positive test. The procedure was repeated with solution 10 only using ammonium
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DETECTION OF T I N GROUP METALS
TABLE II Ammonium Monosulfide (Hi3 for 15 See.) a s a Reagent in Separating the Copper Group from the Tin Group 100 Mg. of Eorb M e l d lndirorrd ns Sulfide Plus
1. Hg, Pb, Bi, Cu, Cd, As+++ 100 mg. 2. Hg, Pb. Bi, Cu, Cd. As+++ 10 mg. 3. Hg. Pb, Bi, Cu, Cd, As+++ 5 mg. 4. Hg, Pb, Bi. Cu. Cd. Sb++' 100 mg. 5. Hg, Pb, Bi, Cu, Cd, Sb+++ 10 mg. 6. Hg, Pb. Bi, Cu. Cd, Sbt++ 5 mg. 7. Pb. Bi. Cd. Sb+++5 mg. 8. Pb, Ri. Cu, Cd, SuC+. 9. Pb, Bi, Cu, Cd, Sn++ 10 mg. 10. Pb, Bi, Cu, Cd. Sn++5 mg. 11. Pb. Bi, Cd, Sn++ 5 mg. 12. Pb, Bi, Cu, Cd, As+++ 5 mg., Sb+++ 5 mg., Sn++ 5 mg. 13. Pb, Bi. Cu. Cd, Ase++ 5 mg., Sb+++ 5 mg., Sn++ 10 mg. 14. Pb, Bi, Cd, As+++5 mg., S b C + +5 mg., S n f + 5 mg. 15. Pb, Bi, Cu, Cd, Asf++200 mg., Sb+++5 mg., S n f + 10 mg. 16. Pb,Bi, Cu, Cd.AsC++5mg., Sbf++200 mg., Sn++ 10 mg. 17. Pb, Bi, Cu, Cd, As+++ 5 mg., SbC++5 mg., S n f + 200 mg. 18. Hg. Pb, Bi, Cu. Cd.
Rcrull of M d d 10"s Addifyi"8 Ammoof Ti" Gmu9 nium Monorulfida Pillrole Dclcclsd in Pol.
Dirty yellow ppt. Yellowish brown ppt. Light brown ppt. Orange red ppt. Brown ppt. Brown ppt. Light orange ppt. Dirty yellow ppt. Brown ppt. Brown ppt. Light brown ppt.
As As As Sb Sb Sb Sb sn su None Sn
Brown ppt.
As, Sb
Brown ppt
As, Sb, Sn
Brown ppt.
As, Sb, Su
Yellow ppt.
As, Sb, Sn
Orange ppt.
As, Sb, Sn
Yellowish brown ppt. Very small amount of brown ppt.
As, Sb. Sn None
polysulfide instead of the monosulfide and a negative test was also obtained for Sn++. It was noticed that if any e n + + was present when reducing the tin solution with an iron nail (3) it was necessary t o continue the reduction until the solution had become colorless. I n all experiments in which Sn++ was used the proper amount of solid SnC12.2Hz0 was used in order to be sure the tin was present in the stannous condition. The amount of precipitate obtained on acidifying the filtrate from the experiment using solution 18 was very much smaller than that in any of the experiments where only 5 mg. of a tin group metal was present. Thus when no precipitate or only a slight amount is obtained on acidifying the ammonium monosulfide filtrate the absence of the tin group can be inferred. It was necessary t o determine whether or not the presence of tin group sulfides undissolved by the ammonium monosulfide would give tests for copper group metals or interfere with their detection. A number, af solutions of known composition were made and the above procedure re-
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peated with the addition of testing the residue from the ammonium monosulfide treatment for the copper group metals (4). Table I l l gives the results of these experiments. TABLE m COPPITGroup Mdalr
Comporilion of ihc Solulian
Found i n Ke.~iduc
1. AsC++ 150 mg., SbC++150 mg., Sn++ 150 mg. 2. Pb 100 mg., Bi 100 mg., Cu IOOmg., Cd 100 mg., As+++ 150 mg., Sb+++ 150 mg., Sn++ 150 mg. 3. Hg 100 mg., Pb 100 mg.. Bi 100 mg., Cu 100 mg., Cd 100 mg., As+++ 250 mg., Sb+++ 250 mg. 4. Pb 5 mg.. Bi 5 mg., Cu 5 mg., Cd 5 mg., As++ 150 mg., Sb+++ 150 mg.. S n f + 150 mg. 5. Hg 5 mg., Pb 5 mg.. Bi 5 mg., Cu 5 mg., Cd 5 mg.. As+++250 mg., Sb+++250 mg.
Tin C ~ a x pMdolr Found i n Filtrnle
None
As. Sb, Sn
Pb, Bi, Cu, Cd
As, Sb, Sn
Hg. Pb, Bi. Cu. Cd
As, Sb
Pb, Bi, Cu, Cd
As. Sb, Sn
Hg, Pb, Bi, Cu, Cd
As, Sb
The results above show the following facts: tin group sulfides do not give tests for any of the copper group metals; when tin group sulfides are present in the copper group sulfides they do not interfere with the detection of the copper group metals; 5 mg. of the copper group metals can be detected in the presence of 150mg. each of As+++,Sb+++, and Sn++, or 250 mg. each of As+++ and Sb+++in the original solution.
Summary 1. The action of various ammonium monosulfide solutions on each of the sulfides of the copper and tin groups was determined. 2. The best ammonium monosulfide solution for the separation of the copper and tin groups and the detection of the latter was selected and its use tested. 3. By means of this solution the presence or absence of the tin group can be established. 4. Using this solution for the separation of the copper from the tin group, 5 mg. of As+++ and Sb+++ and, omitting Hg++, 10 mg. of Sn++ can be detected in the presence of 100 mg. of each of the copper group metals. If Cu++ is also absent then 5 mg. of Sn++ will give a positive result. 5. Tin group metals neither give confirmatory tests for the copper group metals nor do they interfere with their detection. Literature Cited (I) NOYES, A. A., AND BRAY."A System of Qualitative Analysisfor the Common Elements." J.Am. Chem. Soc., 29,169 (Feb., 1907).
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NOYES,A. A.. "Qualitative Chemical Analysis," 9 t h ed., The Maemillan Co.,New York City, 1926, p. 72. (3) CURTMAN, "Method of Analysis for the Metals of Group ZB," Copyright manuscript. 1925. ( 4 ) BASKERVILLE AND CURTMAN. "Qualitative Analysis." 2nd ed.. The Macmillan Co., New York City. 1926, p. 66. (2)
