prof. Viktor Kanický, Analytická chemie I
1
QUALITATIVE ANALYTICAL CHEMISTRY

Qualitative analysis
prof. Viktor Kanický, Analytická chemie I
2
nAnalytical chemistry is the chemistry discipline concerned with the chemical composition of
materials. Analytical chemistry also is concerned with developing the tools used to examine
chemical compositions.
nQualitative analysis deals with the detection of the nature of the chemical species in a sample.
nElemental qualitative analysis is used to separate and detect cations and anions in a sample
substance.

Qualitative analysis
nClassical qualitative inorganic analysis is a method of analytical chemistry which seeks to find
elemental composition of inorganic compounds. It is mainly focused on detecting ions in an aqueous
solution, so that materials in other forms may need to be brought into this state before using
standard methods. The solution is then treated with various reagents to test for reactions
characteristic of certain ions, which may cause color change, solid forming and other visible
changes.[1]
nQualitative inorganic analysis is that branch or method of analytical chemistry which seeks to
establish elemental composition of inorganic compounds through various reagents.
n
n
prof. Viktor Kanický, Analytická chemie I
3

prof. Viktor Kanický, Analytická chemie I
4
Qualitative analysis
nEvidence, detection
qChemical methods
q„Instrumental“ methods (spectroscopic, electrochemical)
n
nObservations, evidence
qSensoric  (crystals, homogeneity, olfactory assessment - smell, colour)
qChanges depending on physical conditions (heating, coloration of flame)
qAnalytical reactions  between examinated substance and analytical reagent (acid-base reactions,
precipitation reactions, complex forming reactions, redox reactions, catalytic r.)
q
nIonrganic qualitative analysis– ionic reactions
q

prof. Viktor Kanický, Analytická chemie I
5
Procedure for qualitative analysis
1.Sampling, sample description
2.Preliminary tests
3.Transfer of sample into solution
4.Detetion of cations in 1/3 of sample solution
5.Detection of anions in 1/3 of sample solution
6.Verification of results in the remaining solution
7.Conclusion of analysis
n
qGuidelines
A)Sample size Þ working technique
B)Preliminary tests
C)Only those elements that are expected to be present in solution based on preliminary tests should
be tested
D)Results of analyses must agree with observations
n

prof. Viktor Kanický, Analytická chemie I
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Preliminary tests
nNature of the sample
qHeating in flame in presence of air
nBurning (organic substances)
nvolatilization, sublimation (ammonium salts)
nMelting (salts of alkali metals)
nResidue after ignition (heavy metlas compounds Þ oxides)
nFlame test – coloration (Na, Ca, K, Ba, Cu, B)
qTest with H2SO4
ndiluted: gas evolution at cold (CO2 carbonates, NO2 nitrites) by heat (SO2 from sulphites and
thiosulphates, H2S sulphides, HX           halogenides)
nconcentrated: carbonization of organic substances, oxidation of Br- and I- evolution of Br2 a I2
n

prof. Viktor Kanický, Analytická chemie I
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Selectivity and implementation of analytical reactions
nAccording to the degree of selectivity we distinguish analytical reactions:
qGroup r. » group reagents – for separation of cation groups
qSelective r. » selective reagents – at certain conditions proof of limited groups of cations –
detection of one cation require more selective reactions
qSpecific » under prescribed condition only one cation is proved
nAccomplishment of reactions
qTest tube (5 ml, 1 ml), micro test tube (0,1 ml)
qDrop (0,3 ml)
qMicroscope 0.01 ml
q    D = P/(V.106), P = observation limit (μg), V (ml), D = limiting dilution, pD = - log D
n

prof. Viktor Kanický, Analytická chemie I
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Detection of cations
nhistory: Boettger, Fresenius – different properties of sulphides
nreagents: HCl, H2S, (NH4)HS, (NH4)2CO3
n
1.Insoluble chlorides
2.Sulphides precipitating in acidic
3.Sulphides and hydroxides precipitating from ammoniacal medium
4.Insoluble carbonates
5.Cations that do not precipitate with any of above reagents
6.
nThis separation is used no more (gaseous sulphane!)
nInstead: group reactions preformed parallell in aliquot parts of a sample

prof. Viktor Kanický, Analytická chemie I
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DETECTION OF CATIONS, GROUP REACTIONS, SELECTIVE REACTIONS

prof. Viktor Kanický, Analytická chemie I
10
Cations detection – group reactions
1.HCl: Ag+, Hg22+, Pb2+
•Ag+: AgCl + hν ® Ag (reduction, graying) dissolves in: CN-, S2O32-, NH3;
q AgCl + 2 NH3 ® [Ag(NH3)2]+ + Cl-  [Ag(NH3)2]+ + 2 H+ ® AgCl + Cl-
•Hg22+: Hg2Cl2 + 2 NH3 ® Hg + Hg(NH2)Cl + NH4+ + Cl-
•Pb2+: PbCl2 dissolves in hot water
•
2.H2SO4: Pb2+, Ba2+, Sr2+, Ca2+ white precipitates
3.
3.H2S (H+): Ag+, Hg22+, Pb2+, Hg2+, Cu2+, Cd2+, Bi3+, Sb3+, Sn2+, Sn4+
•Coloured sulphides: CdS, Sb2S3, SnS2, others are black
•H2S is low dissociated in acidic medium , and therefore, only the least soluble sulphides
•also disproportionation: 3 CuS ® Cu2S + CuS + S
n

prof. Viktor Kanický, Analytická chemie I
11
Cations detection – group reactions
4.NH4HS: Fe2+, Fe3+, Cr3+, Al3+, Co2+, Ni2+, Mn2+, Zn2+
•Higher degree of dissociation of NH4HS to S2- than H2S in acid medium, therefore, more soluble
sulphides precipitate
•NH4HS precipitates at the same time cations presented at 3) (their sulphides are less soluble)
•FeS, Fe2S3, CoS, NiS – black
•ZnS – white, MnS – light, oxidation Þ darkening
•Cr3+, Al3+ - alkaline medium Þ Al(OH)3 white, transparent, Cr(OH)3 green, sulphides are not formed
•CoS, NiS – aging, polymerization, unlike other sulphides are insoluble in HCl
•In excess of NH4HS are dissolved:
q Sb2S3 + 3 S2- ® 2 SbS33-
q SnS2 + S2- ® SnS3
q after acidification they precipitate again

prof. Viktor Kanický, Analytická chemie I
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Cations detection – group reactions
5.NaOH: Ag+, Hg22+, Pb2+, Hg2+, Cu2+, Cd2+, Bi3+, Sb3+,  Sn2+/4+, Fe2+/3+, Cr3+, Al3+, Co2+, Ni2+,
Mn2+, Zn2+
•Do not precipitate: Ba2+, Sr2+, Ca2+ partially, Mg precipitates ~ pH > 9; alkali metals; NH4+
•Amorphous slimy precipitates: alkaline salts® hydroxides
•In excess of NaOH amphoteric hydroxdes dissolve: Pb(OH)2, Sb(OH)3, Sn(OH)2, Sn(OH)4, Cr(OH)3,
Al(OH)3, Zn(OH)2 Þ employed for separation of cations
•Noble metals:
q Ag+ ® Ag2O brown
q Hg2+ ® HgO yellow
•Dismutation: Hg22+ + 2 OH- ® HgO + Hg + H2O (turns black)
•Oxidation of hydroxides Mn2+/3+, Co2+/3+ Fe2+/3+ discoloration
q Mn: light® brownish
q Co: light® brownish
q       Fe: světle zelený ® reddish brown

prof. Viktor Kanický, Analytická chemie I
13
Cations detection – group reactions
6.NH4OH: Ag+, Hg2+, Pb2+, Hg2+, Cu2+, Cd2+, Co2+, Ni2+, Zn2+, Mn2+, Bi3+, Sb3+,  Sn2+/4+, Fe2+/3+,
Al3+, Cr3+
•Do not precipitate: alkali metals; Ba2+, Sr2+, Ca2+, Mg2+
•In excess of NH4OH amphoteric hydroxdes do not dissolve : Pb(OH)2, Sb(OH)3, Sn(OH)2, Sn(OH)4,
Cr(OH)3, Al(OH)3, Zn(OH)2
•In excess of NH4OH soluble ammincomplexes are formed, and therefore hydroxides dissolve Ag+, Cd2+,
Zn2+, Cu2+, Co2+ to coloured (Cu2+ blue, Co2+/3+ oxidation by air  – red Co(III) complex) or
colourless (Ag, Cd, Zn) complexes
•Hg22+ + X- + 2 NH3 ® HgNH2X + NH4+ + Hg
q Hg2+ + X- + 2 NH3 ® HgNH2X + NH4+
q 2 Hg2+ + 4 NH3 ® (Hg2N)+ + 3 NH4+  Millon base
•

prof. Viktor Kanický, Analytická chemie I
14
Cations detection – group reactions
7.KI: Ag+, Hg2+, Pb2+, Hg2+, Cu2+, Bi3+
•AgI – pale yellow, PbI2 – yellow, soluble in hot water to colourless solution, HgI2 – red, Hg2I2 –
yellow-green, BiI3 - brownish
•excess of iodide – complex-forming features:
•PbI2 + I- ® [PbI3]-
•Hg2I2 + 2 I- ® [HgI4 ]2- + Hg
•BiI3 + I- ® [BiI4]-
•hydrolysis:
q BiI3 + H2O ® BiOI (orange) + 2 H+ + 2 I-
•redox reactions:
q Cu2+ + 4 I- ® 2 CuI (white) + I2
q Hg2I2 ® HgI2 + Hg (graying)
q 2 Fe3+ + 2 I- ® 2 Fe2+ + I2  brown colour of solutions by              iodine
•

prof. Viktor Kanický, Analytická chemie I
15
Cations detection – group reactions
8.Hydrolytic reactions: Bi3+, Sn2+/4+, Sb3+
•hydroxocomplexes, basic salts and hydroxides are formed at increasing pH – splitting of H+ from
H2O in hydration shells of cations
•hydrolysis:
•a) by diluting with water
•b) by addding of acetate buffer HAc/Ac-, pH 5
•significant hydrolysis – in teh form of chlorides:
q Bi3+ + H2O + Cl- ® BiOCl + 2H+
•

prof. Viktor Kanický, Analytická chemie I
16
Separation of cations
solution, filtrate
additional group
reactions
precipitate
BaSO4, CaSO4,
PbSO4
Selective
reactions
Na+, K+, Mg2+
solution, filtrate
group reaction
H2SO4
precipitate
AgCl, Hg2Cl2,
PbCl2
Results
verification
Separ. of HM
 by NH4HS
Selective
reactions
Group
reaction HCl
Ident. NH4+
SAMPLE

prof. Viktor Kanický, Analytická chemie I
17
Separation of cations – Selective reactions
nRemoving of cations of heavy metals  HM
qNH4HS Þ precipitation of sulphides
qMgO, var Þ MgO + H2O ® Mg(OH)2
q Me2+ + Mg(OH)2 ® Me(OH)2 + Mg2+
n
Sample+ MgO, boiling
centrifugation
Solution
Li+, Na+, K+, Ca2+, Sr2+, Ba2+
verification by NH4HS
Precipitate of hydroxides
including amphoteric

prof. Viktor Kanický, Analytická chemie I
18
Group of poorly soluble chlorides
Hg22+, Ag+, Pb2+
Reagent HCl (1:1)
Hg2Cl2, AgCl, PbCl2 ↓ white
Hot water
↓ Hg2Cl2, AgCl
Pb2+ solution
Diluted NH3
↓ HgNH2Cl + Hg (black)
Ag(NH3)2Cl solution

prof. Viktor Kanický, Analytická chemie I
19
Selective reactions of cations forming poorly soluble chlorides
Sample + 1 mol.l-1 H2SO4
            centrifugation
solution
addition of 2M HCl
and centrifugation
precipitate
addition of H2S
turns black due to PbS
+ NH3 1:1
centrifugation
HgNH2Cl + Hg0
crystals AgCl
microscope,
Tananajev reaction

prof. Viktor Kanický, Analytická chemie I
20
Selective reactions of cations forming poorly soluble chlorides
nHg22+:
1.Hg2Cl2 + 2 NH3 ® NH4Cl + HgNH2Cl ↓ bílá + Hg0 ↓ (grey precipitate)
2.Hg22+ + 2 I- ® Hg2I2 ↓ yellow-green                                                 (turns black
by resulting Hg)
3.Hg22+ + CrO4- ® Hg2CrO4 ↓ červenohnědá
4.catalytic oxidation of Al0 (Hg22+, Hg2+, Hg0),                                       interferes
Cu2+, Bi3+, AsIII
n

prof. Viktor Kanický, Analytická chemie I
21
Selective reactions of cations forming poorly soluble chlorides
nAg+:
1.AgCl + 2 NH4OH « Ag(NH3)2+ +  2H2O + Cl- ,                              evolution of NH3 Þ
precipitation of AgCl – microscope
2.Ag+ + Br- ® AgBr ↓ yellowish (in NH3 only bleaches, does not dissolve)
3.Ag+ + I- ® AgI ↓ yellow (no reaction with NH3)
4.2 Ag+ + CrO4- ® Ag2CrO4 ↓ red-brown
5.Redox Tananajev
reaction                                                                              Mn(OH)2 + 2
Ag+ + 2 OH- ® 2 H2O + MnO2  ↓ brown + 2 Ag  ↓ black
6.Ag+ + rhodamine + H+ ® žlutooranžová ↓
n

prof. Viktor Kanický, Analytická chemie I
22
Selective reactions of cations forming poorly soluble chlorides
nPb2+:
1.Pb2+ + H2SO4 ® PbSO4 ↓ white + 2H+;                                              PbSO4 + 3 NaOH ®
Pb(OH)3- + SO42- + 3 Na+; difference from BaSO4
2.PbSO4 + S2- ® PbS + SO42- ↓ black;                                     oddělení Ba2+ od Pb2+:
NH4OH ® Pb(OH)2; Ba2+, 2 OH-
3.PbSO4 + K2CrO4 ® PbCrO4 ↓ yellow + 2 K+ + SO42-
4.Pb2+ + 2 I- ® PbI2 ↓ yellow (golden rain),                                                in
excess of I- converts to [PbI4]2- - colourless solution
5.Pb2+ + difenylthiokarbazone ® red↓

prof. Viktor Kanický, Analytická chemie I
23
Sulphides precipitating from acid medium
Hg2+, Bi3+, Cu2+, Cd2+
Reagent H2S v H+ at 70°C
HgS black↓, Bi2S3 brown↓, CuS black↓, CdS yellow↓
Reagent HNO3 (1:1)
HgS black↓
Bi3+, Cu2+, Cd2+ (NO3-) solutions
činidlo NH3 [NH4OH]
CdS yellow↓
Bi(OH)3 white↓
[Cu(NH3)4]2+ blue solution
[Cd(NH3)4]2+ colourless solution
1M H2SO4 + Fe-chips
Cd2+ solution
Cu brown↓
CdS yellow↓
Reagent KCN
[Cu1+(CN)4]3- colourelss solution
[Cd2+ (CN)4]2- colourelss solution
Reagent H2S
Reagent H2S

prof. Viktor Kanický, Analytická chemie I
24
Sulphides precipitating from acid medium and soluble in (NH4)2Sx
H2S in H+
As2S3 ↓ yellow
As2S5 ↓ yellow,
 only in H+
Sb2S3 ↓ orange
Sb2S5 ↓ orange
SnS ↓ brown
SnS2 ↓ yellow
As3+, As5+, Sb3+, Sb5+, Sn2+, Sn4+
(NH4)2Sx
AsS43-, SbS43-, SnS32- + S ↓ pale yellow
HAc (1:1)
Boiling of precipitates S2- with HCl
As2S5 ↓ yellow
Sb3+,5+, Sn2+,4+ roztoky
Boil down to lower volume na menší objem
and reduct with Fe-nail
Sb ↓ black
Sn2+,4+ solutions  → flame test,
blue luminescence

prof. Viktor Kanický, Analytická chemie I
25
Selective reactions of cations forming low soluble sulphides in acid (2M HCl)
nH2S + H2O « HS- + H3O+
nHS- + H2O « S2- + H3O+
qHgS black
qCuS black
qBi2S3 brown
qCdS yellow
qSb2S3 orange-red
qSnS brown
qSnS2 yellow
nSnS2 soluble in excess of NH4HS to SnS32-
qAs2S3 yellow, As2S5 yellow, only in H+
q
nammonia-based separation
n Hg2+, Cu2+, Cd2+, Sn2+, SnIV, Sb3+, Bi3+
n

prof. Viktor Kanický, Analytická chemie I
26
Selective reactions of cations forming low soluble sulphides in acid (2M HCl)
+ 1M H2SO4 + Fe chips
centrifugation, boiling
1 ml sample
+ 1:1 NH3
+ NaAc separation
Cd(NH3)42+ colourless
Cd(NH3)42+ colourless
Cu(NH3)42+ blue
Me(OH)n precipitates
Me = Bi, Sb, Sn,
HgNH2Cl, HgO
disssolution
precip. Bi, Sb, Sn
in acid
+ addition NH4HS →
CdS yellow precipitate
Fe2+ + 2e- → Fe (-0,44 V)
Cd2+ + 2e- → Cd (-0,40 V)
Cu2+ + 2e- → Cu (+0,34 V)
Reduction of  Cu
+ addition H2S →
CdS yellow precipitate

prof. Viktor Kanický, Analytická chemie I
27
Selective reactions of cations forming low soluble sulphides in acid (2M HCl)
nHg2+
1.Reaction with
SnCl2:                                                                              Sn2+ + 2 Hg2+ +
2 Cl- → Hg2Cl2 ↓ white (turns gray /black) + SnIV              removing of interfering Pb2+, Ag+,
Hg22+ by addition of 2M HCl
2.Catalytic oxidation of Al
3.Reaction with KI : Hg2+ + 2 I- → HgI2 red precipitate                         HgI2  + 2 I- →
[HgI4]2- soluble complex, interferes Bi3+ by BiI3 + I- → [BiI4]- yellow solution, elimination by
adding Cu2+, disprop. CuI (white), sorption of HgI2 on CuI, BiI3 dissolves
4.Hg2+ + difenylthiokarbazone + OH- → red-orange solution
Hydrolysis  in NaAc
Bi3+ precipitates
Sb(OH)4-, Sn(OH)62-,
Sn(OH)3- in solution
Dissolution of
precipitates Bi, Sb, Sn
in mineral acid

prof. Viktor Kanický, Analytická chemie I
28
Selective reactions of cations forming low soluble sulphides in acid (2M HCl)
nCu2+
1.Reaction with
K4[Fe(CN)6]:                                                                              Cu2+ +
[Fe(CN)6]4- → Cu2[Fe(CN)6] ↓ red-brown  = Hatschett
brown                                                    precipitate of variable composition
CuK2[Fe(CN)6], Cu2K[Fe(CN)6] in neutral or weak acid medium; precipitate is soluble in NH3 and in
diluted mineral acids; interferes Fe3+ (Berlin blue), removed by NH3
2.Reaction with Kupral (Sodium diethyldithiocarbamate trihydrate)
n(C2H5)2NCSSNa.3H2O, results in brown precipitate of chelate 1:2, extraction to chloroform CHCl3
trichloromethane, low soluble chelates interfere, reaction is selective in NH3 leachate and when
masking with EDTA
3.Cu2+ + salicylaldoxim + H+ → pale yellow↓ (salicylaldehyde oxime)
qC6H4CH=NOH-2-OH.
3.

prof. Viktor Kanický, Analytická chemie I
29
Selective reactions of cations forming low soluble sulphides in acid (2M HCl)
nCd2+
1.Reaction with gaseous H2S or by addition of sulphane water forms yellow precipitate
CdS
  after separation of HM: interfere Hg, Ag, Pb, Cu, Bi, Sb, Sn, ammonia separation, in solution
remains Ag+, Cu2+, Cd2+, reduction of Ag+, Cu2+ by means of Fe
2.Cd2+ + 2 OH- → Cd(OH)2 ↓ white
3.
nBi3+
1.Reaction with thiourea Þ yellow soluble complex (pH < 1) {Bi[S=C(NH2)2] 3}3+; interferes Sb3+ ,
elimination by oxidation to SbV by KMnO4 and SbV masking by F-
2.Reduction by 3 SnII + 2 Bi3+ → 2 Bi0 + 3 SnIV, bismuth = black metal; interfere Ag+, Hg22+ -
removing by 2M HCl, interferes Hg2+, than detection of Bi3+ by hydrolysis to BiOCl
3.

prof. Viktor Kanický, Analytická chemie I
30
Selective reactions of cations forming low soluble sulphides in acid (2M HCl)
nSb3+
1.Sb3+ hydrolytically separated by means of  NaAc, then reduction by Fe in acid medium → black
pulverized antimony and  H2; interferes Cu2+, this is eliminated by removing of hydrolysates
2.after oxidation by KMnO4 to SbV coloured ion associate with crystal violette is formed  {SbCl6-;
B+} extraction to benzene
3.Sb3+ + Na2S2O3 → ↓ red precipitate of antimony vermilion
4.Marsh-Liebig test, antimony mirror does not move with heat
5.
nSn2+, Sn4+
1.Luminescence reaction in flame – blue emission of SnCl, interferes Cu2+ - green flame, therefore
prior to test is reduced by Fe

prof. Viktor Kanický, Analytická chemie I
31
Group of other sulphides and hydroxidů precipitated by ammonium hydrogensulphide
Co2+, Ni2+, Fe2+, Fe3+, Mn2+, Al3+, Zn2+, Cr3+
Reagent (NH4)2S v NH4Cl and NH4OH medium
činidlo HCl (1:4)
Fe2+, Fe3+, Mn2+, Al3+, Zn2+, Cr3+ (Cl-) solutions
NaOH (20%) + H2O2 (5%)
Fe(OH)3 ↓ reddish brown
Mn(OH)2 ↓ reddish brown
CrO42- yellow solution
AlO33- [Al(OH)4]- cl. solution
ZnO22- [Zn(OH)4]2- cl. solution
+ 1 drop of H2O2
+ 1M H2SO4
+ extr. izoamylalcohol
+ 1 drop of alizarine
+ 2M CH3COOH
+ 20% HCl
+ [Fe(CN)6]3-
blue extract Cr3+
red solution Al3+
yellow-green↓ Zn2+
H2O2 (5%) + H+
CoSO4, NiSO4 solutions
CoS ↓ black, NiS ↓ black
CoS black↓, NiS black ↓, FeS black ↓, Fe2S3 brownish ↓, MnS flesh-pink↓,
Al(OH)3 white↓, ZnS white↓, Cr(OH)3 grey-blue-green ↓

prof. Viktor Kanický, Analytická chemie I
32
Selective reactions of Co2+, Ni2+, Fe2+, Fe3+, Mn2+, Al3+, Zn2+, Cr3+
precipitates
Cr(OH)3, Al(OH)3,
Fe(OH)3, Fe(OH)2,
Mn(OH)2, Co – basic salt
1 ml 1M NH3
1 drop of sample
centrifugation
solutions
[Zn(NH3)6]2+
[Co(NH3)6]2+
[Ni(NH3)4]2+

prof. Viktor Kanický, Analytická chemie I
33
Selektivní reakce kationů Co2+, Ni2+, Fe2+, Fe3+, Mn2+, Al3+, Zn2+, Cr3+
nFe3+
1.s thiokyanatanem (SCN)- v kyselém prostředí                                    Fe3+ + SCN- →
červené komplexy [Fe(SCN)]2+, [Fe(SCN)2]+… Fe[Fe(SCN)6] typický krvavě červený roztok; ruší
fluoridy
2.s K4[Fe(CN)6] v kys. prostředí vzniká sraženina nebo koloidní roztok Berlínské modři
K{FeIII[FeII(CN)6]} respektive FeIII4[FeII(CN)6]3; ruší Cu2+ ve velkém nadbytku
3.s kyselinou sulfosalicylovou v kys. prostř. vzniká fialový roztok rozpustného chelátu; ruší
fluoridy a dihydrogenfosforečnany
4.Fe3+ + 3 NH3 + 3 H2O → 3 NH4+ + Fe(OH)3 ↓ rezavě hnědá,                  v nadbytku
NH3 nerozpustná
5.
nFe2+
1.s 1,10-fenanthrolinem při pH 2-9 vzniká stabilní červený chelát
2.s kynoželezitanem K3[Fe(CN)6] vzniká Berlínská modř
3.bezvodé soli Fe2+ jsou bílé, hydratované světle zelené: FeSO4.7H2O, (NH4)Fe(SO4)2.6H2O (Mohrova
sůl) a FeCl2.4H2O
4.
4.
n

prof. Viktor Kanický, Analytická chemie I
34
Selektivní reakce kationů Co2+, Ni2+, Fe2+, Fe3+, Mn2+, Al3+, Zn2+, Cr3+
nAl3+
1.s alizarinem S (1,2-dihydroxyantrachinon-3-sulfonan) vzniká červený lak – chelát AlL, povrchově
adsorbován na Al(OH)3 v NH3 prostředí, ruší: Fe3+, Cu2+ - oddělení pomocí NaOH
2.s kvercetinem – vzniká zeleně fluoreskující, ve vodě málo rozpustný Al - chelát při pH 1-4, ruší:
Zn2+ a Sb3+ – nepatrná fluorescence, maskování: F-
3.
nCr3+
1.s peroxidem H2O2 v alkalickém prostředí za varu → CrO42- žlutý roztok, po okyselení přechází s
přebytečným peroxidem na nestálý modrý peroxid CrVIO5, ruší: Mn2+ - alkalické dělení
2.Cr3+ + 3 NH3 + 3 H2O → 3 NH4+ + Cr(OH)3 ↓ šedozelená
3.

prof. Viktor Kanický, Analytická chemie I
35
Selektivní reakce kationů Co2+, Ni2+, Fe2+, Fe3+, Mn2+, Al3+, Zn2+, Cr3+
nZn2+
1.s kyanoželeznatanem K4[Fe(CN)6] v prostředí 1M HCl vzniká bílá sraženina K2Zn[Fe(CN)6]; ruší
Fe3+, Cu2+, Mn2+, Ni2+ a Co2+ - dělení v 10% NaOH
2.s difenylthiokarbazonem v alkalickém prostředí vzniká zelený roztok, vytřepáním v roztoku
CCl4 přechází na purpurovou červeň
3.
nCo2+
1.s thiokyanatanem vzniká modrý rozpustný komplex [Co(SCN)4]2-, extrakce např. do izoamylalkoholu,
ruší Fe3+, Bi3+ - maskování s F-, Cu2+ tvoří hnědou sraženinu
2.bezvodé soli jsou modré, hydratované růžové např.: CoCl2.6H2O, Co(NO3)2.6H2O, CoSO4.7H2O
3.Co2+ + 2 NH3 + 2 H2O → ↓ světle modrá zásaditých solí, rozpouští se v nadbytku NH3 na
[Co(NH3)4]2+, který oxiduje na [Co(NH3)6]3+ (hnědý roztok)
4.s 1-nitroso-2-naftolem vzniká červenohnědá sraženina chelátu CoL3, ruší Cu2+, Fe3+, Hg2+, Ni2+ -
jejich cheláty se v 10% HCl rozloží
5.

prof. Viktor Kanický, Analytická chemie I
36
Selektivní reakce kationů Co2+, Ni2+, Fe2+, Fe3+, Mn2+, Al3+, Zn2+, Cr3+
nMn2+
1.oxidací v kyselých roztocích jodistanem za horka vzniká fialový MnO4-
2.Mn2+ + 2 NH3 + 3 H2O → bílá ↓ zásaditých solí, v důsledku oxidace hnědne
3.bezvodé soli jsou bezbarvé hydratované růžové: MnSO4.7H2O, Mn(NO3)2.6H2O, MnCl2.4H2O
4.
nNi2+
1.s diacetylaldioximem (Čugajevovo činidlo) v amoniakálním prostředí vzniká růžově červená
sraženina chelátu Ni(DH)2
2.Ni2+ + 2 NH3 + 2 H2O → ↓ zásadité soli, v nadbytku NH3 vznik [Ni(NH3)4]2+ modrý roztok
3.hydratované soli Ni2+ jsou zelené, bezvodé jsou bezbarvé
4.
4.
n

prof. Viktor Kanický, Analytická chemie I
37
Skupina kationtů kovů alkalických zemin
Ba2+, Sr2+, Ca2+
NH4Cl nasycený roztok
NH4OH 1:1
(NH4)2CO3 nasycený roztok
BaCO3 bílá ↓, SrCO3 bílá ↓, CaCO3 bílá ↓
rozpustit v CH3COOH (1:1)
přidat CH3COONa 10%
přidat K2Cr2O7 30%
BaCrO4 žlutá ↓
Sr2+, Ca2+ roztoky
(NH4)2SO4 40%
SrSO4 bílá ↓
Ca2+ roztok + (NH4)C2O4 3%
→ CaC2O4 bílá ↓ + 2 NH4+

prof. Viktor Kanický, Analytická chemie I
38
Selektivní reakce alkalických kovů a kovů alkalických zemin
nLi+, Na+, K+, NH4+
qbezbarvé, dobře rozpustné soli; netvoří stabilní komplexy
qplamenové zkoušky (ne NH4+) - zbarvení emisí alkal. kovů
qreakce s organickými činidly
1.
nCa2+, Sr2+, Ba2+
qsraženiny: SO42-, CrO42-, OH-, F-, C2O42-, CO32- rozpustnost:
nSO42-, CrO42- :        Ca2+ > Sr2+ > Ba2+
nOH-, F-, C2O42- :     Ca2+ < Sr2+ < Ba2+
nCO32- :                    Ca2+ ≈ Ba2+ < Sr2+
1.

prof. Viktor Kanický, Analytická chemie I
39
Selektivní reakce alkalických kovů a kovů alkalických zemin
nplamenové zkoušky – těkavé chloridy, Pt drát
qLi2+ karmínově červená 670,0 nm
qNa+ žlutá 589,6 a 589,0 nm
qK+ fialová + červená 404,7 a 768,0 nm
qCa2+ cihlově červená 620,0 nm
qSr2+ červená + oranž. 674,7; 662,8 a 606,0 nm (oranž.)
qBa2+ zelená 531; 524 a 514 nm
q

prof. Viktor Kanický, Analytická chemie I
40
Selektivní reakce alkalických kovů a kovů alkalických zemin
nLi+
1.LiCl je rozpustný v organických rozpouštědlech ´ chloridy Na, K, Ca a Ba, vhodné pro oddělení pro
plamenovou zkoušku
2.
nNa+
1.s octanem uranylo-zinečnatým v kyselině octové vzniká světle žlutá krystalická sraženina
NaMg(UO2)3(CH3COO)9.9H2O, ruší TK
2.
nK+
1.s dipikrylaminem vzniká oranžovo-červená sraženina draselné soli hexanitrodifenylaminátu, ruší
TK, NH4+
2.s kyselinou pikrovou vzniká pikran draselný žlutá sraženina
3.
nNH4+
1.s Nesslerovým činidlem v alkalickém prostředí vzniká hnědá až žlutá
sraženina;
              příprava Ness. činidla: HgCl2 + 2KI ® HgI2 … + 2KI ®
[HgI4]2-;                                        v NaOH reakce [HgI4]2-  + NH4+ ® Hg2I3NH2  ruší
všechny kationty, které se srážejí v alkalickém prostředí
2.
2.

prof. Viktor Kanický, Analytická chemie I
41
Selektivní reakce alkalických kovů a kovů alkalických zemin
nMg2+
1.s Magnezonem (4-nitrobenzen azorezorcin nebo 4-nitrobenzenazo-1-naftol) v NaOH tvoří modrou
sraženinu chelátu; slepý pokus: žlutá ® fialová               v roztoku (acidobazický indikátor);
modrý chelát – zbarvení při adsorpci na Mg(OH)2
2.s thiazolovou (titanovou) žlutí vzniká červená sraženina; slepý pokus dává žlutý až oranžový
roztok
3.s 8-hydroxichinolinem v alkalickém prostředí vzniká žlutá sraženina (jehličky)
4.
4.
nCa2+
1.s kyselinou šťavelovou ve slabě kyselém prostředí vzniká bílá krystalická sraženina šťavelanu
vápenatého; Neruší Sr2+, Ba2+, alkalické kovy, ruší TK -  odstranění s MgO
2.
nSr2+
1.žlutá sraženina s K2CrO4 po oddělení TK, ruší Ca2+, na rozdíl od Ba2+ se nesráží Sr2+ ve 2
mol.l-1 kys. octové
n
nBa2+
1.sráží se s K2CrO4 ve 2 mol.l-1 HAc, v neutr./ alkal. prostředí, sráží se 1 mol.l-1 H2SO4