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GROUP II CATIONS As +3 , As +5 , Sb +3 , Sb +5 , Sn +2 , Cu +2 , Cd +2 , Bi +3

GROUP II CATIONS As +3 , As +5 , Sb +3 , Sb +5 , Sn +2 , Cu +2 , Cd +2 , Bi +3. , Hg +2 , Pb +2. GROUP II CATIONS As +3 , As +5 , Sb +3 , Sb +5 , Sn +2 , Cu +2 , Cd +2 , Bi +3. The specific reactions of Group II cations when they are alone =

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GROUP II CATIONS As +3 , As +5 , Sb +3 , Sb +5 , Sn +2 , Cu +2 , Cd +2 , Bi +3

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  1. GROUP II CATIONS As+3, As+5, Sb+3, Sb+5, Sn+2, Cu+2, Cd+2, Bi+3 , Hg+2, Pb+2

  2. GROUP II CATIONS As+3, As+5, Sb+3, Sb+5, Sn+2, Cu+2, Cd+2, Bi+3 Thespecificreactions of Group II cationswhentheyarealone = Theexperimentsyouwillperformwithknownsamples of group II cations.

  3. Cu+2 1-The solutions of Cu salts have blue or bluish-green color. You can predict the presence of Cu in your sample just by looking at the color of your sample. 2-Reaction with K4[Fe(CN)6] (potassium ferrocyanide) : Red-brownprecipitatesareformedandtheyaresoluble in dilutedammonia 2Cu+2 + [Fe(CN)6] –4 → Cu2[Fe(CN)6] ↓ 3- Reactionwith KCN (potassiumcyanide): Firstlygreenish-yellow Cu(CN)2 ↓ precipitatesareformedanduponexcessadition of KCN, it will be dissolvedbyformation of K3[Cu(CN)4] (potassiumcyanocuprate)

  4. Cd+2 1-ReactionwithH2S: colloidalandyellowcoloredCdS is formedand it is soluble in HNO3. Cd+2 +H2S → CdS ↓ (yellow) + 2H+ 3CdS + 8H+ + 2NO3– → 3Cd+2 + 3S + 2NO + 4H2O 2- ReactionwithKCN: Inthebeginning, whitecoloredCd(CN)2 precipitatesareformedanduponaddition of excess KCN it is dissolvedbyformation of K2[Cd(CN)4] (potassiumtetracyanocadmate(II)) complex. Thiscomplex can reactwith H2S toproduceCdS CdSO4 + 2 KCN → Cd(CN)2 + K2 SO4 Cd(CN)2 + 2 KCN → K2[Cd(CN)4] K2[Cd(CN)4] + H2S → CdS ↓ + 2KCN +2HCN Yellow Thelastreaction is thedifferencebetween Cd+2and Cu+2 , K3[Cu(CN)4] complexdoes not reactwith H2S while K2[Cd(CN)4] reacts.

  5. Bi+3 ** Main oxidationstates of bismuthare +3, –3, +5. Bi-3behavesstrongreducingagentwhile Bi+5 is strongoxidizingagent. 1-Reactionwith Na2SnO2 (Sodiumstannite ): Bismuth is reducedtoblackcoloredmetallic Bi0 2Bi(OH)3 + 3Na2SnO2 → 2Bi0↓+ 3Na2SnO3 + 3H2O black 2-Reactionwith KI: Bi+3 + KI→ BiI3 ↓ blackprecipitate BiI3 + KI ↔ [BiI4]– Solublecomplex

  6. Sn+2 (Tin) The hydrolysis of Sn+2 salts produce white precipitates of Sn(OH)Cl. 1-Reaction with H2S: Brown SnS precipitates. Brown precipitate might turn to black later 2-Tin reduce Bi+3 to black Bi0 in basic medium. Add NaBiO3 (sodiumbismuthate) prepared in basicmedium.

  7. Sn+2 (Tin) • 3- Luminescence test: • The sample is directly used without any pretreatment. • Fill a test tube with cold tap water. • Put 5 mL sample into a small beaker. • Add 3 mL HCl into the beaker. • Add Zn granules (2 microspatula) into the beaker. • Immerse the test tube into the beaker. • Hold the bottom of the test tube directly intothereducingzone of the flame) • Blue shining (luminescence) indicates the presence of Sn+2 • Luminescence is seen outside of the test tube.

  8. As+3, As+5 (Arsenic) Theyboth form strongcovalentbondswithoxygen in water As+3 : AsO3–3, AsO2– (arsenite) As+5 : AsO4–3 (arsenate) 1-Reaction with AgNO3 yields yellow colored Ag3AsO4 (silver arsenate). 3Ag+ + AsO4- → Ag3AsO4↓ yellow

  9. Sb+3, Sb+5 (Antimony) It can producewhitecoloredSbOClprecipitates in water. 1- Reactionwith H2S: Orange Sb2S3 (antimonysulfide) precipitates 2Sb+3 + 3H2S → Sb2S3 ↓ + 6H+ orange ... brown 2- ReactionwithNaOH: White coloredSbOClprecipitates. SbCl3 + NaOH → SbOCl ↓ + HCl + NaCl white

  10. Pb2+ (Lead) Reactionwithpotassiumchromate (K2CrO4): yellowleadchromateprecipitates Pb2+ + K2CrO4 → PbCrO4↓(s) + 2K+ yellowprecipitates • Hg+2 (Mercury) • Copper strip (Amalgam test): • A piece of copper wireis cleaned with 8-10 drops of concentrated HNO3 solution in the watchglass, then it is dried byfilterpaper and mercurysamplesolutionis added to thecopper strip.Mercuryions reduceandcoat the copper strip (bright gray colored).

  11. Insystematicanalysis of cations, 13 cationsareprecipitated as theirsulfides. Amongthesecations, 8 of themhavelowersolubilities in waterandtheyarecalled as Group II cationswhiletheremaning 5 cationswithhighersolubility in waterarecalled as Group III cations: Kspvalues of Group II andGroup III cations When a sulfide reactant is added, in a medium of 0.3 M acid, Group II cations with lower solubility precipitate while Group III cations having higher solubility remain in the solution. Forthisreason, adjustment of acidity is important in separation of thesetwogroups.

  12. Theequilibriumforhydrogensulfide: H2S ↔ 2 H+ + S–2 = 6,8 x 10–23 Inthisequilibrium, [H+] = 0.3 M since theacidity of themedium is adjustedto 0.3 M and [H2S]=0.1 M since thehighestconcentration of it is 0.1 M at 25oC consideringthesolubility: = 6,8 x 10–23 [S–2] = 7,5 x 10–23 AmongGroup III cations, NiS has thelowestsolubilityand in ourcoursesthesamplesareprepared in 0.01 M: Q= [Ni+2] [S–2] = 0,01 x 7,5 x 10–23 = 7,5 x 10–25 7,5 x 10–25 < Ksp (1,4x10-24) Since Q is smallerthanKspNiSdoes not precipitate. TheotherGroup III cationshavehigherKspthanNiSandall of themstaydissolved. On theotherhand Q of Group II cationsarehigherthanKsp of them in thismediumand it meansallGroup II cationswill be precipitated.

  13. Thioacetamide can be used as sulfidesource. Hydrogensulfidewill be producedwhenthioacetamidesolution is heated. Forthisreason, the test tubecontainingyoursamplewill be heated in a waterbathafteraddition of requiredamount of thioacetamide. Since theproducedhydrogensulfidewillimmediatelyreactwithcations in thesample, hazardouseffects of hydrogensulfidesuch as rotteneggsmellwill be reduced. Intheanalysis, theflowchartwill be followed. Sulfides of Group II cationshavedifferentcolorssoyoumayhavepreliminaryinformation at thebeginning of theanalysis: Bi2S3,HgS, CuS, PbS = Black As2S3, As2S5 = Yellow CdS = Pale yellow Sb2S3, Sb2S5 = Orange / red / brown SnS = Brown

  14. GROUP II CATIONS • 40 drops of sample • 4 drops of concentratedHCl • 14 drops of thioacetamide (11%, w/v) and heat in water bath (5 min) • Centrifuge (3000 rpm, 4 min)decant the liquid part • Wash the precipitate with the washing solution • (washing solution: 2 drops of NH4Cl, 2 drops of thioacetamide and 16 drops of distilled water) • HgS, CuS, CdS, PbS, Bi2S3 As2S3, SnS, Sb2S3 • 20 drops of 3 M KOH • Heat in water bath for 3 min • PRECIPITATE A: HgS, CuS, CdS, PbS, Bi2S3 • SUPERNATANT A: AsO3-3, AsS3-3, SbO2-, SbS2-, SnO2-2 • Washwith 10 drops of 3M KOH andwashwith 20 drops of distilledwater • 24 drops of 6 M HNO3 • Heating in a water bath for 5 min • Add 3 M HCluntilthesupernatant is mildacidic. Precipitateswill be fomedif at leastone of theanalyteexist in thesample. • Discardthesupernatantandkeeptheprecipitate. • Add 20 drops of concentratedHCl. • Heat in a waterbathfor 5 min. Divideintotwoparts • PRECIPITATE B: HgS SUPERNATANT B: Pb2+, Bi+3, Cu+2, Cd+2 • 2 drop of 6 M H2SO4 • Evaporatethesolvent in a crucible. • Cool it untilroomtemperature • Add 40 drops of distilledwaterandstir. • SUPERNATANT E: Sn+4 ve Sb+3 • PRECIPITATE E: As2S3 ve As2S5 • Dissolve in 16 drops of aquaregia. • Dry it up in a cruicible • Dissolve it in 2-3 mLdistilledwaterandpour it onto a cupperwire. Hg test is positiveifthecupper is coveredwithgraycolored Hg. Sb+3 test Sn+4 test • Washwith 10 drops of distilledwaterforthreetimes. • Add 20 drops of concentrated HNO3. • Heatandstir in a waterbathfor 5 min • Add 10 drops of 0.5 M AgNO3andstir. • Add 10 drops of 2.5 M sodiumacetate. As3+ is positiveifred-browncolored Ag3AsO4precipitatesareformed. • Add 6 drops of thioacetamideandheat in a waterbath. Sb+3 test is positiveiforangecolored Sb2S3precipitatesareformed. • AdddropbydropNaOHuntilthesolution is basic. • Addfewdrops of Sodiumbismuthatesolution. Sn+4 test is positiveifblackprecipitatesareformedafter a while. • PRECIPITATE C: PbSO4 SUPERNATANT C: Bi+3, Cu+2, Cd+2 • Washprecipitate • Add 20 drops of NH4CH3COO, 6 drops of 6 M CH3COOH and 4 drops of 1M K2CrO4. Pb test is positiveifyellowprecipitatesareformed. • Add NH4OH untilthesolution is basicandthenaddexcess 3 drops of NH4OH SUPERNATANT D: Cu+2, Cd+2 • PRECIPITATE D: Bi(OH)3 • Washprecipitate • Add 10 drops of Na2SnO2. Bi test is positiveifthecolor of precipitateturnstoblack. Cu test is positiveifthesupernatant C is blue. Ifsupernatant C is blue Ifsupernatant C is not blue • Adddropbydrop 1 M KCN untilbluecolordisappears. • Addexcess (2-3 drops) KCN • Add 6 drops of thioacetamide (11% w/v) • Heat it in a waterbathfor 5 min. Cd test is positiveifyellowishprecipiatesareformed. • Add 6 drops of thioacetamide (11% w/v) • Heat in a waterbathfor 5 min. Cd test is positiveifyellowishprecipiatesareformed.

  15. GROUP II CATIONS • 40 drops of sample • 4 drops of concentratedHCl • 14 drops of thioacetamide (11%, w/v) andcentrifuge (3000 rpm, 4 dk) • Afterheating in waterbathfor 5 min, decanttheliquidpartandwashprecipitatewiththewashingsolution • (washingsolution: 2 drops of NH4Cl, 2 drops of thioacetamideand 16 drops of distilledwater) • HgS, CuS, CdS, PbS, Bi2S3 As2S3, SnS, Sb2S3 • 20 drops of 3 M KOH • Heating in waterbathfor 3 min • PRECIPITATE A: HgS, CuS, CdS, PbS, Bi2S3 • SUPERNATANT A: AsO3-3, AsS3-3, SbO2-, SbS2-, SnO2-2 • Washwith 10 drops of 3M KOH andwashwith 20 drops of distilledwater • 24 drops of 6 M HNO3 • Heating in a waterbathfor 5 min • Add 3 M HCluntilthesupernatant is mildacidic. Precipitateswill be fomedif at leastone of theanalyteexist in thesample. • Discardthesupernatantandkeeptheprecipitate. • Add 20 drops of concentratedHCl. • Heat in a waterbathfor 5 min. Divideintotwoparts • PRECIPITATE B: HgS SUPERNATANT B: Pb2+, Bi+3, Cu+2, Cd+2 • 2 drop of 6 M H2SO4 • Evaporatethesolvent in a crucible. • Cool it untilroomtemperature • Add 40 drops of distilledwaterandstir. • SUPERNATANT E: Sn+4 ve Sb+3 • PRECIPITATE E: As2S3 ve As2S5 • Dissolve in 16 drops of aquaregia. • Dry it up in a cruicible • Dissolve it in 2-3 mLdistilledwaterandpour it onto a cupperwire. Hg test is positiveifthecupper is coveredwithgraycolored Hg. Sb+3 test Sn+4 test • Washwith 10 drops of distilledwaterforthreetimes. • Add 20 drops of concentrated HNO3. • Heatandstir in a waterbathfor 5 min • Add 10 drops of 0.5 M AgNO3andstir. • Add 10 drops of 2.5 M sodiumacetate. As3+ is positiveifred-browncolored Ag3AsO4precipitatesareformed. • Add 6 drops of thioacetamideandheat in a waterbath. Sb+3 test is positiveiforangecolored Sb2S3precipitatesareformed. • AdddropbydropNaOHuntilthesolution is basic. • Addfewdrops of Sodiumbismuthatesolution. Sn+4 test is positiveifblackprecipitatesareformedafter a while. • PRECIPITATE C: PbSO4 SUPERNATANT C: Bi+3, Cu+2, Cd+2 • Washprecipitate • Add 20 drops of NH4CH3COO, 6 drops of 6 M CH3COOH and 4 drops of 1M K2CrO4. Pb test is positiveifyellowprecipitatesareformed. • Add NH4OH untilthesolution is basicandthenaddexcess 3 drops of NH4OH SUPERNATANT D: Cu+2, Cd+2 • PRECIPITATE D: Bi(OH)3 • Washprecipitate • Add 10 drops of Na2SnO2. Bi test is positiveifthecolor of precipitateturnstoblack. Cu test is positiveifthesupernatant C is blue. Ifsupernatant C is not blue Ifsupernatant C is blue • Adddropbydrop 1 M KCN untilbluecolordisappears. • Addexcess (2-3 drops) KCN • Add 6 drops of thioacetamide (11% w/v) • Heat it in a waterbathfor 5 min. Cd test is positiveifyellowishprecipiatesareformed. • Add 6 drops of thioacetamide (11% w/v) • Heat in a waterbathfor 5 min. Cd test is positiveifyellowishprecipiatesareformed.

  16. ATTENTION!!! *Whileworkingwith KCN (For Cu+2and Cd+2tests), themediummust be strictlycheckedwithlitmuspaperforitsbasicity. Ifthesolution is acidic, thenhighlytoxic HCN gas is evolved. KCN + H+ → HCN (g)

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