Analisis-Kation

Slide 1

Analisis Kation

The general procedure for separating ions in qualitative analysis

Add precipitating ion

Centrifuge

Add precipitating ion

Centrifuge

A qualitative analysis scheme for separating cations into five ion groups

Add 6M HCl

CentrifugeAcidify to pH 0.5; add H2S

CentrifugeAdd NH3/NH4+ buffer(pH 8)

CentrifugeAdd (NH4)2HPO4

Centrifuge

A qualitative analysis scheme for separating cations into five ion groups

Add 6M HCl

CentrifugeAcidify to pH 0.5; add H2S

CentrifugeAdd NH3/NH4+ buffer(pH 8)

CentrifugeAdd (NH4)2HPO4

Centrifuge

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Hot waterPb2+AgCl(s); Hg2Cl2(s)

NH3

HgNH2Cl(s)Ag(NH3)6+

YellowPutih

Group I Kation

Group II KationCuSSub Golongan TembagaSub Golongan ArsenBi2S3As2S3Sb2S3SnS2CdSPbSHgSAs2S5HitamHitamKuningHitamHitamKuningKuningOrangeKuning

PbSCuSBi2S3CdSHitamHitamHitamKuning

AsS4-3SbS4-3SnS3-2HgS2-2

Na2S2

Group II KationSub Golongan Tembaga

PbSCuSBi2S3CdSHitamHitamHitamKuningSPb+2 Cu+2 Bi+3 Cd+2dibuang

Cu+2 Bi+3 Cd+2PbSO4putih

PbSO4putih

HNO3 encer (6M)H2SO4 pekatPbSO4putih

Bi(OH)3putih

Cu(NH3)4+2 Cd(NH3)4+2

NH4OH berlebih Cu2Fe(CN)6CdSHCl (6M), K4Fe(CN)6

KCN, H2S

Group II KationSub Golongan ArsenAs2S5 HgS Sb2S3 SnS2dibuang

Sb+3 Sn+2

HCl encerHCl pekatSb, MgSn+2 HgCl2

AsS4-3SbS4-3SnS3-2HgS2-2As2S3Sb2S3SnS2HgSAs2S5HitamKuningKuningOrangeKuningAs2S5 HgSAs. Oksalat, H2S

Sb2S3Mg, HCl (6M)

dibuangHg Hg2Cl2

Group III Kation

Group III Separation Scheme

Background Group III Separation SchemeGroup III unknown

NiS, FeS, MnS, Fe(OH)3, Al(OH)3, ZnS

Group IV ionsNH3, H2S, Heat

A Preparation of Group III cationsThe group III ions are initially separated from the bulk solution by precipitation as either insoluble metal sulfides or hydroxides.

Ni2+(aq) + S2(aq) D NiS(s) (black) Fe2+(aq) + S2(aq) D FeS(s) (black) Zn2+(aq) + S2(aq) D ZnS(s) (white) Mn2+(aq) + S2(aq) D MnS(s) (pink) Al3+(aq) + 3 OH(aq) D Al(OH)3(s) (white, gel)

Background Group III Separation SchemeGroup III unknown

NiS, FeS, MnS, Fe(OH)3, Al(OH)3, ZnS

Group IV ionsNH3, H2S, Heat

A Preparation of Group III cationsSince iron has two common oxidation states, its chemistry in this step is more complex.If iron(III) is present it is reduced to iron(II) and elemental sulfur in produced.2 Fe3+(aq) + H2S (aq) 2 Fe2+(aq) + S(s) + 2 H+(aq)

Background Group III Separation SchemeNiS, FeS, MnS, Fe(OH)3, Al(OH)3Ni2+, Fe3+, Mn2+, Zn2+, Al3+WasteHCl, HNO3, Heat

B1 Separation of Group III cationsFollowing the precipitation, the metal ions are combined with acid to form the free (and soluble) metal ions.

3NiS(s) +8H+(aq) + 2NO3(aq) 3Ni2+(aq) + 2NO(g) + 3S(s) + 4H2O(l)

FeS(s) + 2 H+ (aq) Fe2+(aq) + H2S(aq)

3Fe2+(aq) + 4H+(aq) + NO3(aq) 3Fe3+(aq) + NO(g) + 2H2O(l)

MnS(s) + 2 H+(aq) Mn2+(aq) + H2S(aq)

ZnS(s) + 2 H+(aq) Zn2+(aq) + H2S(aq)

Al(OH)3(s) + 3 H+(aq) Al3+(aq) + H2O(l)

Background Group III Separation SchemeNi2+, Fe3+, Mn2+, Zn2+, Al3+Al(OH)4-, Zn(OH)42-Fe(OH)3, Ni(OH)2, Mn(OH)26 M NaOH

B2 Separation of Group III cationsAluminum and zinc ions are amphoteric.This means that at high acid or base concentrations, these metals form soluble complexes, but precipitate at moderate pH.Iron, manganese and nickel form insoluble hydroxides at high pH.Fe3+(aq) + 3 OH(aq) D Fe(OH)3(s) (rust-color)

Ni2+(aq) + 2 OH(aq) D Ni(OH)2(s) (green)

Mn2+(aq) + 2 OH(aq) D Mn(OH)2(s) (light brown)


B2 Separation of Group III cationsAluminum and zinc ions are amphoteric.This means that at high acid or base concentrations, these metals form soluble complexes, but precipitate at moderate pH.Iron, manganese and nickel form insoluble hydroxides at high pH.Al3+(aq) + 3 OH(aq) D Al(OH)3(s) (white, gelatinous)

Zn2+(aq) + 2 OH(aq) D Zn(OH)2(s) (white)


B2 Separation of Group III cationsExcess AcidAl(OH)3(s) + 3H+(aq) D Al3+ + 3 H2O(aq)

Zn(OH)2(s) + 2H+(aq) D Zn2+ + 2 H2O(aq)


B2 Separation of Group III cationsExcess BaseAl(OH)3(s) + OH(aq) D Al(OH)4-(aq)

Zn(OH)2(s) + 2OH(aq) D Zn(OH)42-(aq)

Background Group III Separation SchemeFe(OH)3, Ni(OH)2, Mn(OH)2Fe3+, Ni2+, Mn2+C1 Test for Mn2+, Fe3+, Ni2+HNO3, KNO2

The precipitate is redissolved by adding acid to the precipitate.The addition of nitric acid neutralizes the sodium hydroxide and regenerates the free cations.There is no easy method which will allow Mn2+, Fe3+ and Ni2+ to be separated; therefore, the sample is divided.

DivideSample

Background Group III Separation SchemeDivideSampleMnO4-purpleNaBiO3

C2 Test for Mn2+If sodium bismuthate is added to a solution containing manganese(II), a redox reaction occurs resulting in the formation of the purple permanganate ion.14H+(aq) + 2Mn2+(aq) + 5BiO3-(s) 2 MnO4-(aq) + 5Bi3+(aq) + 7H2O(l)Fe3+, Ni2+, Mn2+

Background Group III Separation SchemeDivideSampleD1 Separation of Fe3+ and Ni2+Fe(OH)3Ni(NH3)62+Conc. NH3

The nickel and iron ions can be separated by the addition of ammonia.The increased pH causes the formation of the insoluble iron(III) hydroxide.The nickel ion combines with ammonia to form a soluble complex ion, hexaamminenickel(II).Fe3+(aq) + 3NH3(aq) + 3H2O(l) 3NH4+(aq) + Fe(OH)3(s) (brown) Ni2+(aq) + 6NH3(aq) D Ni(NH3)62+(aq) (blue) Fe3+, Ni2+, Mn2+

Background Group III Separation SchemeDivideSampleD2 Test for Fe3+Fe(OH)3Ni(NH3)62+Conc. NH3

Fe(SCN)63-blood redHCl / NH4SCN

The presence of the iron(III) ion is confirmed by the addition of ammonium thiocyanate.If iron(III) is present, a blood red solution forms.Fe3+(aq) + 6SCN-(aq) D Fe(SCN)63-(aq) blood redFe3+, Ni2+, Mn2+

Background Group III Separation SchemeDivideSampleE Test for Ni2+Fe(OH)3Ni(NH3)62+Conc. NH3

Fe(SCN)63-blood redHCl / NH4SCN

Ni(DMG)2strawberry red ppt.H2DMG

The presence of the nickel ion is confirmed by the addition of dimethylglyoxime.Dimethylglyoxime combines with the nickel ion to form a complex which forms a strawberry red precipiate.

Ni(NH3)62+(aq) + 2 HC4H7N2O2(aq) 4NH3(aq) + 2NH4+(aq) + Ni(C4H7N2O2)2(s) (red) Fe3+, Ni2+, Mn2+

Background Group III Separation SchemeAl(OH)4-, Zn(OH)42-F1 Separation of Al3+ and Zn2+Al(OH)3Zn(NH3)42+NH3HNO3

Careful control of pH allows for the separation of aluminum and zinc ions.The solution is made very slightly basic.At these conditions, the aluminum ion precipitates as aluminum hydroxide.The zinc ion remains in solution.Al3+(aq) + 3 NH3(aq) + 3 H2O(l) D 3 NH4+(aq) + Al(OH)3(s)

Zn2+(aq) + 4 NH3(aq) D Zn(NH3)42+(aq)

Background Group III Separation SchemeAl(OH)4-, Zn(OH)42-F2 Test for Al3+Al(OH)3Zn(NH3)42+NH3HNO3

Al(OH)3 aluminoncherry red ppt.NH3, aluminon

A successful test for aluminum requires that the previous reactions and their pH control were properly performed.If not, false positive tests result.The test for aluminum requires the free aluminum ion to react with ammonia in the presence of a reagent called aluminon and form a red precipitate.Be careful, if there is iron or zinc left in the sample, a red precipitate will form resulting in a false positive.Al3+(aq) + 3 NH3(aq) + 3 H2O + aluminon(aq) D 3 NH4+(aq) + Al(OH)3aluminon(s) (red)

Background Group III Separation SchemeAl(OH)4-, Zn(OH)42-F2 Test for Al3+Al(OH)3Zn(NH3)42+NH3HNO3


To confirm that the red precipitate is the aluminum complex, ammonium carbonate is added.If the red color does not fade, aluminum is present.

Background Group III Separation SchemeAl(OH)4-, Zn(OH)42-G Test for Zn2+Al(OH)3Zn(NH3)42+NH3HNO3


K2Zn3[Fe(CN)6]2white ppt.K4Fe(CN)6

To test for the zinc ion, a solution of potassium hexacyanoferrate(II) is added to the test solution.If zinc is present a white precipitate forms.The exact color of the precipitate can vary depending on the presence of other ions.If iron is present the color can change to yellow, green or blue.3 Zn2+(aq) + 2 K+(aq) + 2 Fe(CN)64 (aq) D K2Zn3[Fe(CN)6]2 (s)

Background Group III Separation Scheme

Zn2+Al3+Ni2+Fe3+Mn2+

Group IV Kation

Group IV Separation SchemeB Test for Ba2+The formation of a yellow precipitate on the addition of potassium chromate indicates the presence of the barium ion.

HC2H3O2,K2CrO4

BaCrO4yellow ppt.Ba2+6M HCl

Flame Testapple - greenBaSO4white ppt.6M H2SO4

Ba2+(aq) + K2CrO4(aq) BaCrO4(s) + 2K+(aq)

Group IV Separation SchemeB Test for Ba2+A flame test (apple green) is used to confirm the presence of the ion.HC2H3O2,K2CrO4



Background Group IV Separation SchemeB Test for Ba2+The final test for barium is the formation of a white precipitate on the addition of a sulfate to the solution.HC2H3O2,K2CrO4



Ba2+(aq) + H2SO4(aq) BaSO4(s) + 2H+(aq)

Background Group IV Separation SchemeC Test for Ca2+The calcium ion is separated from magnesium by precipitating calcium oxalate.Ca2+, Mg2+CaC2O4(NH4)2C2O4

Mg2+Flame testred-orange6M HCl

Ca2+(aq) + (NH4)2C2O4(aq) CaC2O4(s) + 2NH4+(aq)

Background Group IV Separation SchemeC Test for Ca2+A flame test (red-orange flame) is used to confirm the presence of the calcium ion.Ca2+, Mg2+CaC2O4(NH4)2C2O4


Background Group IV Separation SchemeC Test for Mg2+The magnesium ion is precipitated as a white solid (ammonium phosphate) in an alkaline solution.Ca2+, Mg2+CaC2O4K2C2O4


Mg2+(aq) + NH3(aq) + HPO42-(aq) MgNH4PO4(s)MgNH4PO46H2Owhite ppt.NH3(aq)Na2HPO4(aq)

Group V Kation

A Flame test for Na+ and K+Insoluble salts of sodium and potassium are not known.One method of determining the presence of these ions is the flame test.Group IV UnknownFlame Test Na+orange-yellow flameFlame Test K+lavender flame

Na

K

BaSO4 CaC2O4Test Nyala : Na &KZn(Ac)2 , UO2(Ac)2NaZn(UO2)3(Ac)2.6H2ONa3Co(NO2)6K3Co(NO2)6(NH4)2SO4 (NH4)2C2O4HCl

Original sampleNaOH Bau khas amoniak Merubah lakmus merah menjadi biru

Step 1 Add NH3(aq)Centrifuge

CentrifugeStep 2 Add HCl

Step 3 Add NaOH

CentrifugeStep 4 Add HCl, Na2HPO4

Step 5 Dissolve in HCl and add KSCNA qualitative analysis scheme for Ag+,Al3+,Cu2+, and Fe3+

Step 1 Add NH3(aq)Centrifuge

CentrifugeStep 2 Add HCl

Step 3 Add NaOH

CentrifugeStep 4 Add HCl, Na2HPO4

Step 5 Dissolve in HCl and add KSCNA qualitative analysis scheme for Ag+,Al3+,Cu2+, and Fe3+Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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19-#

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