Modified Analysis of Qualitative Analysis Groups I1 and I11 THOMAS C . HERNDON Eastern Kentucky S t a t e Teachers College, Richmond, Kentucky
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NUMBER of schemes of qualitative analysis have been suggested to avoid the use of hydrogen sulfide as a precipitating agent in qualitative analytical work. Among these schemes may be mentioned those outlined by Brockman,' M u l l i n i ~ ,and ~ Gerstenzang.3 The scheme of analysis which the writer wishes to present does not eliminate the use of sul6des entirely but does: (1) avoid the slowness of the usual gaseous precipitation with Has, (2) reduce the amount of H2Sodors in the laboratory to a minimum, (3) considerably reduce the time for the detection of the cations, and (4) appear about as accurate as the traditional methods. The present modification is confined entirely to the analysis of Groups I1 and 111. Group I is separated and analyzed by the usual methods. Group I1 (in the present modification) consists of those cations which may be precipitated by NHIOH in the presence of NHhCl, namely, mercury(ic), bismuth, lead, antimony, tin, iron, aluminum, and chromium. Group I11 (in the present modification) consists of the remaining cations which may be precipitated by (NH&S in an ammoniacal solution, namely, copper, cadmium, cobalt, nickel, manganese, and zinc. Arsenic is next removed by itself and then the Groups IV and V may be separated and analyzed by the usual methods. Following is an outline of the proposed procedures. QUALITATIVE DETERMINATION OP THE CATIONS
(Procedures 1 to 4, inclusive, show the analysis of Group I. Since this is done by the usual methods, i t is omitted here).
Procedure 5: Test for the phosphate ion: If the phosphate ion is present in the solution, i t will cause the formation of insoluble phosphates of the alkaline earth metals and magnesium when the solution is made alkaline with ammonia. Therefore, the solution must he tested for phosphate ion and precautions taken to retain the alkaline earth metals and magnesium. To about 2 to 3 ml. of the filtrate from Group I (or of the solution for analysis) add an equal volume of a solution of ammonium molybdate and make acid with nitric acid. Heat nearly to boiling for a few minutes. A yellow, finely crystalline precipitate which may form slowly is ammonium phosphomolybdate and shows the presence of the phosphate ion. If BROCKMAN, C. J., "Qualitati~eAnalysis." Ginn and Company, Boston, 1930. MULLINIX, R. D., J. CHEM.EDUC., 1, 67 (1924). a GERSTENZANG, E. M., J. CIIEM.EDUC., 11,369 (1934).
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the test is positive follow procedure 14, when you reach that point in the scheme of analysis. If the test is negative disregard procedure 14 and go on with procedure 15.
Procedure 6: Precipitation of Group II-Hg(ic), Pb, Bi, Sb, Su, Fe, Al, Cr: To the filtrate4 from Group I (or 20 ml. of the solution for analysis) add 2 or 3 g. of solid ammonium chloride and then add, with constant stirring, enough 6 M ammonium hydroxide to make the solution smell strongly of ammonia, AFTER blowing the excess vapor from the surface of the mixture. Filter as quickly5 as possible and reserve the filtrate for subsequent groups. Wash the precipitate two or three times with hot water containing a little ammonium hydroxide. Suction filtration is best a t this point. Procedure 7: Separation of Hg, Sb, and Sn ions from Pb, Bi, Fe, Al, Cr ions: Transfer the group precipitate to an evaporating dish and add 5 to 10 ml. of sodium polysulfide solution depending on the amount of the precipitate. Warm gently but do not boil, and STIR THOROUGHLY. Filter, remove the filtrate containing the thio-salts of Hg, Sb, and Sn, and wash the residue on the filter with a small amount of water containing a few drops of sodium polysulfide solution. Save the residue and proceed with the analysis of the polysulfide filtrate. Procedure 8: Separation and identification of the Hg(ic) ion: Acidify the polysulfide filtrate with hydrochloric acid (HOOD), filter, and wash precipitate. Save the filtrate,6 which should be boiled immediately to remove H2S.I Discard the washings. Place the residue, which is composed of the sulfides of mercury, antimony,
This &ration should be carried out as quickly as possible
sult in the inclusion of manganese in Group I1 and interfere with its detection at the proper place in Group 111. The sodium polysulfide contains free sodium hydroxide which tends to dissolve both aluminum and chromium hydroxides, both of these hydroxides bdng amphoteric. The hydrogen sulfide should he boiled out to prevent its being oxidized atmospherically to sulfuric acid, thus interfering with the test for chromium, due to the formation of white lead sulfate.
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and tin, in an evaporating dish and add 10 ml. of concentrated hydrochloric acid. Boil and stir for two or three minutes and filter. The residue is HgS and the filtrate contains SbCla- and SnC16-. Save the filtrate for procedure 9. Dissolve the residue of HgS in 2 or 3 ml. of aqua regia, boil to destroy excess aqua regia, dilute to 5 ml. with water, filter if cloudy, and add 5 ml. of CLEAR stannous chloride solution. A white precipitate which often has a silky appearance and which may turn gray or even black confirms mercuric ion.
To the filtrate from procedure 10, containing FeCL, AICla, and CrC13,add the filtrate from procedure 8, and make the solution decidedly alkaline with sodinm hydroxide. Then add, little by little and with stirring, about 2 g. of sodium peroxide. Heat to boiling to destroy excess peroxides and filter with suction. The filtrate contains sodium aluminate and sodium chromate. Save this filtrate for procedure 15. The residue of ferric hydroxide, Fe(OH)3, should be thoroughly washed.
Procedure 9: Separation and identification of antimony and tin ions: To the acid liltrate from procedure 8 (ShC4- and SnC16- solution) add three or four iron nails and boil for a few minutes. The tin is reduced to the stannous state and the antimony is reduced to black particles of the free element. ~ e m o v ethe nails and filter off the antimony. To the filtrate, add 5 ml. of mercuric chloride solution. A white, silky precipitate which may turn gray or black confirms stannous ion. To confirm antimony ion, dissolve the black precipitate of free antimony in 3 or 4 ml. of aqua regia, boil to destroy excess aqua regia, dilute to 10 or 15 ml. with water, and pass in hydrogen sulfide. An orange precipitate of Sh2S3confirms antimony ion.
Procedure 13: Identification of iron (ferric ion): Dissolve the ferric hydroxide from procedure 12 in 10 ml. of 2 M hydrochloric acid and add a few ml. of potassium thiocyanate solution. A deep red solution containing the complex ferric-thiocyanate ion confirms the ferric ion.
Procedure 10: Separation of lcad and bisnmth ions from iron, aluminum, and chromium ions: To the residue saved from the polysulfide treatment in procedure 7, add 10 ml. of 2 M hydrochloric acid and stir well. Filter off the undissolved PbS and Bi2S3. Boil and reserve the filtrate which contains FeC13, AICla, and CrCI3. Wash the residue with two small portions of hot water. Procedure 11: Separation and identification of lead and bismuth ions: Transfer the residue of PbS and Bi& from procedure 10 to an evaporating dish and dissolve in a few ml. of concentrated nitric acid. Add. with caution. 2 or 3 ml. of concentrated sulfuric acid i n d evaporate (HOOD) until dense fumes of SOa come off. Cool and carefully add about 10 ml. of water.= If lead ion is present, it will precipitate out as white PbSOd, thus confirming the lead ion. Filter off any PbS04 and discard it. Make the liltrate alkaline with ammonium hydroxide. If bismuth ion is present, it will precipitate as white Bi(OH)J. Filter this off and wash. Pour 5 ml. of sodium stannite9 solution over the precipitate on the filter. An immediate blackening of the precipitate confirm bismuth ion. Procedure 12: Separation of iron ion from aluminum and chromium ion:
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8 If too much water is added there is danger that bismuth ion will precipitate as a basic salt and thus confuse the lead test and lessen the sensitivity of the bismuth test which follows. * Sodium stannite is made by making 2 or 3 ml. of SnCL solution strongly alkaline with sodium hydroxide solution.
Procedure 14:1° Elimination of phosphate ion and recovery of alkaline earth metals and magnesium: If phosphate was shown to be present by procedure 5 add a few ml. of ferric chloride to the solution containing ferric thiocyanate, heat to boiling, and add a small excess of sodium acetate. Continue boilmg until precipitation is complete. Filter off the precipitate of ferric phosphate and basic ferric acetate. Wash the residue with a little water and add the washings to the filtrate. Discard the residue. Make the filtrate alkaline with sodium carbonate, heat to boiling and allow the precipitate, if any, to settle for some minutes. Filter and wash the residue thoroughly to remove all salts of sodium and potassium. The residue is composed of one or more of the following: CaCOa, SrC03, BaC03, MgCOa. Dissolve this residue by pouring 10 ml. of 2 M hydrochloric acid over it on the filter. Wash the paper with a few ml. of water and add filtrate and washings to the filtrate from the arsenic sulfide. -See nrocedure 22. Procedure 15: Separation and identification of aluminnm ion: To the filtrate containing sodium aluminate and sodium chromate from procedure 12 add nitric acid until the solution is acid to litmus. Then add ammonium hydroxide until the solution is alkaline. A white precipitate is probably aluminum hydroxide and indicates the presence of aluminum ion. Filter off this precipitate and save filtrate for procedure 16 to test for chromium ion. Wash the residue on the filter and discard washings. Dissolve residue from the lilter with 5 ml. of 2 M hydrochloric acid, add a few drops of aluminon reagent to the solution, and make alkaline with ammonium carbonate. A red precipitate of the aluminum lake con6rms the aluminum ion. Procedure 16: Identification of the chromium ion: Acidify the filtrate from the aluminum hydroxide
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lo If procedure 5 showed the presence of phosphate ion, carry out procedure 14. If phosphate was found to be absent, disregard procedure 14 and go at once to procedure 15.
precipitate of procedure 15 with acetic acid and add 5 ml. of lead acetate solution. A yellow precipitate of PbCrOl confirms the presence of chromium ion.
droxide solution. A bright red precipitate12confirms nickel ion.
Procedure 20: Separation and identification of zinc Procedure 17: Precipitation of Group 111-Cu, Co, ion: Ni, Cd, Mn, Zn: Treat the solution containing the chlorides of Cd, Mn, and Zu with 6 M sodium hydroxide until it is.deTo the filtrate from Group I1 (or 20 ml. of a solution for analysis) add 5 ml. of ammonium sulfide solution cidedly alkaline. Cadmium and manganese hydroxides to precipitate the sulfides of Cu, Co, Ni, Cd, Zn, Mu. precipitate while the zinc ion forms sodium zincate:. Heat to boiling and filter hot. Reserve filtrate for sub- NarZuOz. Filter, remove the filtrate, wash precipitate, sequent groups. Wash residue with hot water con- and reject washings. Acidify the solution containing taining a little ammonium nitrate. Discard washings, the sodium ziucate with acetic acid and pass in hydrogen sulflde. A white precipitatela of ZnS, soluble in hywhich should be clear." drochloric acid, confirms zinc ion. Procedure 18: Separation of Cu, Co, and Ni ions from Procedure 21: Identification of cadmium and manCd, Mn, Zn ions: ganese ions: Place the group precipitate in a small beaker or Dissolve the hydroxides of cadmium and manganese evaporating dish and treat with 20 ml. of 2 M hydrochloric acid to convert the CdS, MnS, ZnS into the in 10 ml. of 1 M sulfuric acid and divide into two equal corresponding chlorides. The CuS, CoS, NiS are rela- parts. To one part add a few grains of sodium bistively unaffected by this treatment, if i t is com- muthate. A pink or purple color due to the formation pleted in the space of a few minutes. Do not let the of the permangauate ion confirms manganese ion. This acid stay in contact with the residue more than a very color may fade rather quickly, but if it shows a t all, i t few minutes. Filter, reserve the filtrate, and wash the proves the presence of manganese. To the other part residue, discarding the washings, but, of course, reserv- of the solution, add 25 ml. of water and saturate with hydrogen sulfide. A yellow precipitate14 of cadmium ing the residue. sulfide confirms cadmium ion. Procedure 19: Identification of the Cu, Co, Ni ions: Procedure 22: Precipitation and identification of arThese three ions may be detected in the presence of senic: one another. Dissolve the sulfide residue from proAcidify the filtrate from Group I11 (or a prepared cedure 18 in 5 ml. of 6 M nitric acid, heat to boiling, solution for analysis) with hydrochloric acid (HOOD) Filter if not clear. Divide and dilute to about 15 ml. into three portions. To one portion add about 5 ml. and heat just to boiling. Do not boil, for AsCla is ammonium acetate solution and about 5 ml. of po- volatile. A yellow, curdy precipitate indicates artassium ferrocyanide solution. A reddish or mahog- senic. A white precipitate is free sulfur. In any case, any-colored precipitate (sometimes purplish, but al- filter, save filtrate for subsequent groups, and dissolve ways colored) of copper ferrocyanide confirms the cop- residue in 5 ml. of concentrated nitric acid. Add 5 ml. per ion. To a second portion add ammonium acetate of magnesium chloride, filter if cloudy, and make alsolution and 5 ml. of Nitroso-R-salt. A red color kaline with ammonium hydroxide. A white, crystalline precipitate of magnesium ammonium arseuate, (sometimes brownish) in the solution c o ~ cobalt s ion. To the third portiou add 5 ml. of dimethylgly- MgNH4As04, confirms arsenic. (Procedures 23 to 28 are devoted to the separation oxime solution and make alkaline with ammonium hyand analysis of Groups IV and V). 11 If some of the dark-colored precipitate passes through the filter, it is probably NiS or CoS, or both. In this case, add a few c a m s of solid ammonium nitrate to the mixture. heat to boiling For a few minutes, and then filter. The amman& nitrate a d heating usually breaks the colloidal sulfide, causing them to
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12 The addition of 10 ml. water and a few ml. of ether. shakine " and allowina to settle. em~hasizesthe nickel test. '"his p&ipitate m a y m t be snow-white. 1' If no precipitate forms, add 20 ml. more water to reduce the acidity and again saturate with hydrogen sulfide.
