REACTIONS OF DETECTION OF CATIONS OF THE FIRST ANALYTICAL GROUP
Reactions of lithium cations detection:
1. Action of carbonate ammonium. Carbonates of alkaline metals and ammonium form white
precipitate:
(NH4)2CO3 + 2LiCl → Li2CO3↓ + 2NH4Cl
Lithium carbonate soluble in diluted mineral acids and in acetic acids and does not precipitate in
presence of ammonium salts.
2. Action of sodium hydrogenphosphate. Na2HPO4 in neutral or slightly acidic solution forms white
precipitate:
3LiCl +2Na2HPO4 → Li3PO4↓ + NaH2PO4 + 3NaCl
Lithium phosphate easily soluble in solutions of acids, insoluble in alcohol and soluble in
ammonium salts.
3. Action of sodium hexanitrocobaltate (III). The sodium hexanitrocobaltate (ІІІ) in the neutral or
acetic solution forms yellow crystalline precipitate similar to potassium salt:
3LiCl + Na3[Cо(NO2)6] → Li3[Cо(NO2)6] ↓ + 3NaCl
4. Action of ammonium fluoride. In presence of NH4OH ammonium fluoride gives white
amorphous precipitate:
LiCl + NH4F → Li F↓ + NH4Cl
It is possible to use this reaction for the separation of lithium ions from ions of potassium and
sodium.
5. Action of potassium orthoperiodate of iron(III). K2[FeIO6] in neutral or alkali environment at
heating forms yellow amorphous sediment LiK[FeIO6]:
LiCl + K2[FeIO6] → LiK[FeIO6] ↓ + KCl
6. Flame test. Salts of lithium paint colourless flame of gas burner in the intensively red colour.
Reactions of potassium cations detection:
1. Action of sodium hidrogentartrate or tartaric acid. The sodium hydrogentartrate or tartaric acid at
рН 4-5 form white crystalline precipitate:
KCl + NaHC4H4O6 → KHC4H4O6↓ + NaCl
Precipitate potassium hydrogentartrate forms super-saturated solutions. The precipitate dissolves
in the hot water, alkalis and acids:
KHC4H4O6 +HCl → H2C4H4O6 + КCl
KHC4H4O6 +NaОН → KNaC4H4O6 + H2O
Cations reactions
1
Reaction implementation features: For acceleration of precipitate formation the reaction make at
cooling and rubbing by the glass stick on walls of test tube.
Make reaction with the tartaric acid in presence of sodium acetate.
2. Action of sodium hexanitrocobaltate (III). The sodium hexahydrocobaltate(ІІІ) at рН 4-5 forms
yellow precipitate:
2KCl + Na3[Cо(NO2)6] → K2Na[Cо(NO2)6]↓ + 2NaCl
Precipitate is insoluble in acetic acid, dissolves at heating in the strong acids and decomposes by
alkalis with formation of the brown precipitate Cо(ОН)3:
K2Na[Cо(NO2)6] + 6HCl → 2КCl + NaCl + CоCl3 + 6НNO2
K2Na[Cо(NO2)6] + 3NaОН → Cо(ОН)3↓ + 2КNO2 + 4NaNO2
3. Action of hydrogen hexachloroplatinate (IV). Hydrogen hexachloroplatinate in neutral or weak
acidic solution forms yellow crystalline precipitate:
KCl + H2[PtCl6] → K2[PtCl6] ↓ + 2HCl
4. Action of perchloric acid. The perchloric acid forms white crystalline precipitate:
KCl + HClО4 → KClО4↓ + HCl
The potassium perchlorate is partly soluble in water and insoluble in the butyl alcohol.
5. Action of picric acid. Picric acid (trinitrophenol) sediments yellow precipitate from concentrated
solutions of potassium salts:
OK
OH
NO2
O2N
NO2
O2N
++KCl
+ HCl
NO2
NO2
6. Action of dipicrylamine. Dipicrylamine in interaction with potassium-ions substitutes hydrogen
of imide-group on potassium ion and forms orange-red precipitate:
NO2
O2N
NO2 + KCl
NH
NO2
NO2
O2N
O2N
O2N
O2N
NO2
+ HCl
NO2
NK
O2N
7. Flame test. Volatile salts of potassium (KCl) paint flame of gas burner in the pale-violet colour.
Cations reactions
2
Reactions of sodium cations detection:
1. Action of zinc-uranile-aceate. Zn[(UO2)3(CH3COO)8] in neutral or weak acidic solution gives
green-yellow crystalline precipitate, which has brilliant yellow fluorescence:
NaCl + Zn[(UO2)3(CH3COO)8] + CH3COOН + 9Н2О →
→ NaZn[(UO2)3(CH3COO)9]·9H2O↓ + HCl
This reaction can be executed by the drop method. In case of irradiation by the ultraviolet light
the green luminescence exists.
2. Action of potassium hexahydroxystybiate. K[Sb(OH)6] in neutral environment forms white
crystalline precipitate:
NaCl + K[Sb(OH)6] → Na[Sb(OH)6] ↓ + KCl
Na[Sb(OH)6] precipitate is soluble in the hot water and partly in alkalis:
Na[Sb(OH)6] + 2NaОН → Na3SbO4 + 4Н2О
The acids decompose the K[Sb(OH)6] reagent and formed precipitate Na[Sb(OH)6], creating
amorphous precipitate of metha-stybiate acid:
Na[Sb(OH)6] + НCl → Н[Sb(OH)6] + NaCl
Н[Sb(OH)6] → НSbO3↓ + 3Н2О
3. Action of methoxy-phenyl-acetic acid. Solution of 4-methoxy-phenyl-acetic acid with sodium
cations forms white crystalline precipitate:
CH3O
CH2COOH + NaCl
CH3O
CH2COONa
+ HCl
4. Flame test. The sodium salts paint colourless flame of gas burner in yellow. A test is very
sensible to sodium ions.
Reactions of ammonium cations detection:
1. Action of magnesium oxide and sodium hexanitrocobaltate(III). Undergo magnesium oxide on
solutions containing ammonium-ions forms ammonium. Formed ammonium after intersction with
chloride acid and sodium hexanitrocobaltate(III) forms yellow precipitate:
2NH4Cl + Na3[Cо(NO2)6] → ↓(NH4)2Na[Cо(NO2)6] + 2NaCl
2. Action of alkalis. Alkalis at heating with ammonium salts evolve an ammonia:
NH4Cl + NaОН → NH3↑ + NaCl + Н2О
Free ammonia detection methods:
– smell;
– moistened universal indicator paper, placed to opening test tube, from which an ammonia is
eluted, becomes green-blue or dark blue;
Cations reactions
3
– «smoke» formation at placing a glass stick moistened by chloride acid;
– moistened mercury indicator paper, placed to opening test tube, from which an ammonia is
eluted, colour in black as a result of reaction:
2NH3 + Hg2(NO3)2 → Hg↓ + NH2HgNO3↓ + NH4NO3
2. Action of the Nessler’s reagent. The Nessler’s reagent (K2[HgI4]) in alkaline environment with
ammonium salts forms orange-brown precipitate of the Millon’s base:
Hg
NH4Cl + 2K2[HgI4] + 4KOH
H2N
O I + KCl + 7KI + H2O
Hg
Precipitate dissolves in chloride acid and in solutions of alkalis.
Cations reactions
4
REACTIONS OF DETECTION OF CATIONS OF THE SECOND ANALYTICAL GROUP
Reactions of silver cations detection:
1. Action of chloride acid. Chloride acid and water-soluble chlorides form white amorphous
precipitate:
AgNO3 + HCl = ↓AgCl + HNO3
Silver chloride insoluble in diluted nitrate acid, easily soluble in the ammonia solutions and in
ammonium carbonate:
AgCl + 2NН4OН = [Ag(NН3)2]Cl + 2H2O
Addition of acid or potassium iodide solution to the got ammoniac solution of AgCl or AgI
precipitate falls out:
[Ag(NН3)2]Cl + 2HNO3 = AgCl↓ + 2NН4NO3
[Ag(NН3)2]Cl + 2KI = AgI↓ + 2NН3 + KCl
2. Action of iodides. Potassium iodide forms light-yellow precipitate:
AgNO3 + KI = AgI↓ + KNO3
Precipitate is practically insoluble in ammonia (unlike AgCl) and diluted nitrate acid, well soluble
in solution of potassium cyanide and sodium thiosulphate.
3. Action of hydroxides of alkaline metals and ammonium. The alkalis at first form white
precipitate
AgNO3 + NaOH = AgOH↓ + NaNO3
This compound quickly decomposes with formation of the brown precipitate Ag2O:
2AgOH = Ag2O↓ + Н2О
Precipitate is insoluble in the alkali surplus, well soluble in nitrate acid and ammonia solution.
The ammonia in case of addition by drops to the neutral solution of silver salt forms the brown
precipitate Ag2O, which easily dissolves in the ammonia surplus:
AgNO3 + NН4OH = Ag2O↓ + Н2О + NН4NO3
Ag2O + 4NН4OН = 2[Ag(NН3)2]OH + 3H2O
4. Action of hydrogen sulphide. Hydrogen sulphide or ammonia sulphide forms black precipitate:
2AgNO3 + (NН4)2S = Ag2S↓ + 2NН4NO3
Silver sulphide dissolves in concentrated nitrate acid:
3Ag2S + 8НNO3 = 6AgNO3 + 2NO↑ +3S + 4Н2О
Cations reactions
5
5. Action of chromates. Salts of chromic acid form orange-red precipitate:
2AgNO3 + К2CrO4 = Ag2CrO4↓ + 2КNO3
6. Action of dithizone. Dithizone (diphenylthiocarbazone) with the silver cations forms the
complex compound painted in yellow, which is extracted by chloroform and carbon
tetrachloride:
NH
N
NH
C
N
N
SH + AgNO3
N
C
N
SAg + HNO3
N
7. Action to formaldehyde. Formaldehyde easily reduces the silver ion to free metal:
Ag2O + НСOН = 2Ag↓ + HСOОН
As a result of reaction in the test tube walls appears the brilliant plaque of free silver, through what
this reaction got a name “reaction of silver mirror”.
Reactions of lead cations detection:
1. Action of chloride acid. Chloride acid and chlorides with lead cations form white precipitate:
Pb(NO3)2 + 2HCl = PbCl2↓ + 2HNO3
Precipitate is soluble in the hot water and the HCl surplus.
2. Action of hydroxides of alkaline metals and ammonium. Alkalis in the equivalent quantities to
the lead form white precipitate:
Pb(NO3)2 + 2NaOH = Pb(OH)2↓ + 2NaNO3
Precipitate is soluble in acids and alkali surplus (at рН = 13) forming plumbite Na2PbO2.
Ammonium hydroxide forms white precipitate of base salt insoluble in surplus of reagent:
Pb(NO3)2 + NН4OH = Pb(OH)NO3↓ + NН4NO3
3. Action of iodides. Potassium iodide with the lead salts forms yellow precipitate:
Pb(NO3)2 + 2КІ = PbI2↓ + 2HNO3
Precipitate is soluble in surplus of reagent, in hot water, and in acetic acid. Precipitate solubility in
hot water and acetic acid is used for the additional detection of lead cations, since at cooling of
solution the precipitate falls out again as character gold scales.
4. Action of hydrogen sulphide. The hydrogen sulphide forms black precipitate:
Cations reactions
6
Рb(NO3)2 + Н2S = РbS↓ + 2НNO3
Lead sulphide does not dissolve in acetic and mineral acids, unless the concentrated nitrate acid:
3РbS + 8НNO3 = 3Рb(NO3)2 + 2NO↑ +3S + 4Н2О
5. Action of sulphates. The water-soluble sulphates with the lead cations form the white precipitate:
Рb(NO3)2 + Na2SO4 = PbSO4↓ + 2NaNO3
6. Action of chromates. To potassium chromate forms yellow precipitate:
Рb(NO3)2 + К2CrO4 = PbCrO4↓ + 2КNO3
7. Action to sodium of rhodizonate.
O
O
ONa
O
O
O
Pb + 2NaNO3
+ Pb(NO3)2
ONa
O
O
O
O
O
8. Action of dithizone.
NH
N
2
C
N
NH
N
N
N
N
N
C
N
SH + Pb(NO3)2
S
Pb
S
+ 2HNO3
C
N
NH
Reactions of mercury(I) cations detection:
1. Action of chloride acid. The chloride acid with mercury(І) forms white precipitate:
Нg2(NO3)2 + 2HCl = Нg2Cl2↓ + 2HNO3
The precipitate has luminescence by orange-red colour in the ultraviolet light. Ammonia with
mercury(І) chloride forms free mercury, from which the precipitate turns black, and white
precipitate of mercury aminochloride (dismutation of univalent mercury on Нg+2 and Нg0):
Cations reactions
7
Нg2Cl2 + 2NН4OН = НgNН2Cl↓ + Нg↓ + NН4Cl + H2O
2. Action of hydroxides of alkaline metals and ammonium. Hydroxides of alkaline metals with
mercury(І) salt form black precipitate:
Нg2(NO3)2 + 2NаOH = Нg2O↓ + Н2О + 2NаNO3
Solution of ammonium hydroxide with mercury(І) salt forms a mixture, which consists of black
elemental mercury and white mercury aminonitrate:
Нg2(NO3)2 + 2NН4OH = Нg↓ + NН2НgNO3↓ +NН4NO3+ Н2О
3. Action of iodides. Potassium iodide with solutions of mercury(І) salts forms green-grey
precipitate
Нg2(NO3)2 + 2KI = Нg2І2↓ + 2KNO3
Which dissolves in surplus of potassium iodide with colourless complex formation and elemental
mercury:
Нg2І2 + 2KI = K2[НgI4] + Нg↓
4. Action of hydrogen sulphide. The hydrogen sulphide forms mixture of elemental mercury and
sulphide of bivalent mercury as a result of dismutation of Нg2S to НgS and Нg:
Нg2(NO3)2 + Н2S = НgS↓ +Нg↓ + 2НNO3
Mercury(ІІ) sulphide dissolves in “aqua regia”:
3НgS + 6НСl + 2НNO3 = 3НgСl2 + 3S + 2NO + Н2O
5. Action of tin(II) chloride. The mercury(І) reduces to free metal under action of tin(ІІ):
Нg2(NO3)2 + SnCl2 = Нg2Cl2↓ + Sn(NO3)2
Нg2Cl2 + SnCl2 = 2Нg↓ + SnCl4
6. Reaction on copper plate. If to drop solution of mercury(І) salt on the copper coin, through 2-3
min coin will be covered by the grey layer of mercury amalgam, which after grinding by the
wool piece becomes brilliant:
Нg2(NO3)2 + Cu = 2Нg↓ + Cu(NO3)2
Cations reactions
8
REACTIONS OF DETECTION OF CATIONS OF THE THIRD ANALYTICAL GROUP
Reactions of calcium cations detection:
1. Action of sulphate acid and soluble in water of sulphates. The sulphate acid and water-soluble
sulphates with calcium ions form white crystalline precipitate:
CaCl2 + H2SO4 = CaSO4↓ + 2HCl
Saturated solution of ammonium sulphate dissolves precipitate forming a water-soluble complex:
CaSO4 + (NH4)2SO4 = (NH4)2[Ca(SO4)2]
This reaction uses for separation calcium ions from strontium ions.
2. Action of ammonium oxalate. To the ammonium oxalate with calcium salts forms white
crystalline precipitate:
CaCl2 + (NH4)2C2O4 = CaC2O4↓ + 2NH4Cl
Precipitate is insoluble in acetic acid (unlike to oxalates of barium and strontium) and ammonia
solution, soluble in solutions of strong acids with oxalic acid formation:
CaC2O4 + 2HCl = CaCl2 + H2C2O4
3. Action of glyoxal-bis-(2-hydroxyaniline) (Pharmacopoeia). Glyoxal-bis-(2-hydroxyaniline) with
calcium ions in alkali environment forms red complex compound. The product is hardly soluble in
water but well extracts with chloroform.
N
OH
H
C
H
C
+ Ca(OH)2
N
N
OH
H
C
O
H
C
N
Ca
H2O
O
H2O
4. Action of potassium hexacyanoferrate(II) (Pharmacopoeia). Potassium hexacyanoferrate(II) at
pH > 7 and ammonium chloride presence interacts with calcium ions and forms white
crystalline precipitate:
CaCl2 + 2NH4Cl + K4[Fe(CN)6] = ↓Ca(NH4)2[Fe(CN)6] + 4KCl
5. Action of sodium rhodizonate. Sodium rhodizonate in acidic environment forms violet
precipitate with calcium ions:
Cations reactions
9
O
O
ONa
O
O
O
Ca + 2NaCl
+ CaCl2
ONa
O
O
O
O
O
6. Flame test. Volatile salts of calcium paint flame of gas burner in orange-red colour.
Reactions of strontium cations:
1. Action of sulphate acid and soluble in water of sulphates. The sulphate acid and water-soluble
sulphates with strontium ions form white crystalline precipitate:
SrCl2 + H2SO4 = SrSO4↓ + 2HCl
The strontium sulphate is possible to convert to carbonate by boiling with saturated solution of
sodium or potassium carbonate.
1. Action of ammonium oxalate. Ammonium oxalate with strontium salts forms white crystalline
precipitate:
SrCl2 + (NH4)2C2O4 = SrC2O4↓ + 2NH4Cl
Precipitate is soluble in the acetic acid and in solutions of strong acids with oxalic acid formation:
SrC2O4 + 2CH3COOH = Sr(CH3COO)2 + H2C2O4
SrC2O4 + 2HCl = SrCl2 + H2C2O4
2. Action of gipseous water. The gipseous water (saturated solution CaSO4 × 2Н2О) with strontium
ions forms white crystalline precipitate:
SrCl2 + СаSO4 = SrSO4↓ + СаCl2
The precipitate appears after heating or at the room temperature after protracted standing.
3. Action of chromates. To potassium chromate with strontium ions forms yellow precipitate:
SrCl2 + K2CrO4 = SrCrO4↓ + 2KCl
The strontium chromate is soluble in mineral and acetic acids.
1. Action to sodium rhodizonate. Sodium rhodizonate in neutral environment forms brown
precipitate with strontium ions:
Cations reactions
10
O
O
O
ONa
O
O
Sr + 2NaCl
+ SrCl2
ONa
O
O
O
O
O
The red-brown spot forms on filter paper also. This spot disappears after chloride acid addition
(precipitate dissolving).
4. Flame test. Volatile salts of strontium paint flame of gas burner in the carmine-red colour.
Reactions of barium cations:
1. Action of sulphate acid and soluble in water sulphates. The sulphate acid and sulphates with
barium ions form white crystalline precipitate:
BaCl2 + H2SO4 = BaSO4↓ + 2HCl
Precipitate is insoluble in diluted mineral acids.
2. Action of potassium dichromate. Potassium dichromate in presence of sodium acetate with
barium ions forms yellow crystalline precipitate:
2BaCl2 + K2Cr2O7 + Н2О + 2СН3СООNa = 2BaCrO4↓ + 2KCl + 2СН3СООН + 2NaCl
Precipitate is soluble in mineral acids and insoluble in acetic acid.
3. Action of sulphate acid and potassium permanganate. Sulphate acid in saturated solution of
potassium permanganate with barium ions forms violet precipitate, which is not discoloured by
reducers. The KMnO4 crystals are isomorphic to BaSO4 crystals and wedge to the barium
sulphate crystalline grate:
BaCl2 + H2SO4 + KMnO4= BaSO4↓·+ KMnO4+ 2HCl
4. Action of sodium rhodizonate. Sodium rhodizonate with barium salts forms red sediment. On
filter paper arises red-brown spot that changes colour in red after chloride acid addition. It is
specific reaction on barium ions:
O
O
ONa
O
O
O
Ba + 2NaCl
+ BaCl2
O
ONa
O
O
O
O
5. Action of ammonium oxalate. Ammonium oxalate with barium ions gives white crystalline
precipitate:
Cations reactions
11
BaCl2 + (NH4)2C2O4 = BaC2O4↓ + 2NH4Cl
Precipitate is soluble in boiling acetic acid and in solutions of mineral acids with oxalic acid
formation.
6. Flame test. Volatile barium salts paint flame of gas burner in the yellow-green colour.
Cations reactions
12
REACTIONS OF THE FOURTH ANALYTICAL GROUP CATIONS DETECTION
Reactions of aluminium cations detection:
1. Action to sodium or potassium hydroxide. Hydroxides of alkaline metals with aluminium ions
form white precipitate, soluble in reagent surplus:
Al2(SO4)3 + 6NaOH = ↓2Al(OH)3 + 3Na2SO4
Al(OH)3 +3NaOH = Na3[Al(OH)6]
Na3[Al(OH)6] = NaAlO2 + 2H2O +2NaOH
2. Action of ammonium hydroxide. The ammonia solution in the neutral environment with
aluminium ions forms white amorphous precipitate, insoluble in reagent surplus:
Al2(SO4)3 + 6NН4OH = ↓2Al(OH)3 + 3(NН4)2SO4
3. Hydrolysis of aluminium salts. In presence NH4Cl at heating aluminate hydrolyses with
formation of Al(OH)3 precipitate :
NaAlO2 + H2O +NH4Cl = ↓Al(OH)3 + NН3 + NaCl
4. Action of cobalt nitrate (Tenard’s blue formation). Cobalt nitrate at ignition with aluminium
salts on filter paper forms cobalt aluminate of dark blue colour, which named “Tenard’s blue”
(colour of ash):
2Al2(SO4)3 + 2Co(NO3)2 = 2Co(AlO2)2 + 4NО2 + O2 + 6SO3
5. Action of 8-oxyquinoline (oxyne). 8-oxyquinoline with aluminium ions at рН 4,5-10 forms the
yellow inner-complex compound:
N
OH
O
N
3
N
Al
+ Al(OH)3
O
+ 3H2O
O
N
6. Action of alizarin. Alizarin red S with aluminium ions alkaline environment, created by
NH4OH, forms bright red precipitate:
Al2(SO4)3 + 6NН4OH = ↓2Al(OH)3 + 3(NН4)2SO4
Cations reactions
13
O
OH
O
OH
O Al
OH
O
+ Al(OH)3
O
+ H2O
O
Reactions of zinc cations detection:
1. Action of sodium or potassium hydroxide. Hydroxides of alkaline metals with zinc ions forms
white precipitate soluble in reagent surplus with zincates formation:
ZnCl2 + 2NaOH = ↓Zn (OH)2 + 2NaCl
Zn (OH)2 + 2NaOH = Na2ZnO2 + 2H2O
2. Action of ammonium hydroxide. Solution of ammonium hydroxide with zinc ions forms white
precipitate, which dissolves in the reagent surplus with formation of tetra-ammine complex:
ZnCl2 + 2NH3 +2H2O = ↓Zn(OH)2 + 2NH4Cl
Zn(OH)2 + 4NH3 = Zn[(NH3)4](OH)2
3. Action of sodium sulphide. Sodium sulphide with zinc ions forms white precipitate insoluble in
the acetic acid and soluble in diluted HCl:
ZnCl2 + Na2S = ↓ZnS + 2NaCl
ZnS + 2HCl = ZnCl2 + H2S
4. Action of cobalt nitrate (Rinmann’s green formation). Cobalt nitrate at ignition with zinc salts
on filter paper forms cobalt zincate of green colour, which named “Rinmann’s green” (colour of
ash):
Zn(NO3)2 + Co(NO3)2 = CoZnO2 + 4NО2 + O2
5. Action of ammonium tetrarhodanomercurate. Ammonium tetrarhodanomercurate with zinc salts
in weak acidic environment forms white crystalline precipitate:
ZnCl2 + (NH4)2[Hg(SCN)4]= ↓Zn[Hg(SCN)4] + 2 NH4Cl
6. Action of potassium hexacyanoferrate(II). Potassium hexacyanoferrate(II) with zinc salts forms
white precipitate:
3ZnCl2 + 2K4[Fe(CN)6] = ↓K2Zn3[Fe(CN)6]2 + 6KCl
7. Action of dithizone. Dithizone with zinc ions forms red inner-complex soluble in the organic
solvents:
Cations reactions
14
NH
N
C
2
N
NH
N
N
N
C
N
SH + ZnSO4
N
S
Zn
S
N
+ H2SO4
C
N
NH
Reactions of chrome(III) cations detection:
1. Action of sodium or potassium hydroxide. Hydroxides of alkaline metals with chrome(III) ions
form precipitate of green colour, soluble in reagent surplus due to it amphoterric properties:
Cr2(SO4)3 + 6NaOH = ↓2Cr(OH)3 + 3Na2SO4
2. Action of ammonium hydroxide. Solutions of ammonium hydroxide forms precipitate Cr(OH)3,
partly soluble in the reagent surplus with formation of hexamine-chrome(ІІІ) hydroxide:
Cr(OH)3 + 6NH4OH = [Cr (NH3)6](OH)3 + 6H2O
3. Action of sodium hydroxide and hydrogen peroxide. Under H2O2 action in alkaline environment
the chrome(ІІІ) passes to chrome(ІV) and forms chromates having yellow colour:
2NaCrO2 + 3H2O2 +2NaOH = 2Na2CrO4 + 4H2O
4. Action of oxidants. Under action of oxidants (KMnO4, Cl2, (NH4)2S2O8) in acidic environment
are formed dichromates – appears orange colour:
Cr2(SO4)3 + 3(NH4)2S2O8 +4Н2O = Н2Cr2O7 + 3(NH4)2SO4 + 3Н2SO4
5. Reaction of perchromate acid formation. Under action of H2O2 on the formed dichromate-ion
forms chrome peroxide Cr2O5 (or perchromic acid Н2CrO6 ):
Cr2(SO4)3 + 8NaOH = 2NaCrO2 + 3Na2SO4 + 4H2O
2NaCrO2 + 3H2O2 +2NaOH = 2Na2CrO4 + 4H2O
2Na2CrO4 + H2SO4 = Na2Cr2O7 + Na2SO4 + H2O
Н2SO4 + Na2Cr2O7 + 4H2O2 = 2H2CrO6 + Na2SO4 + 3H2O.
If to reactionary mixture add a mixture of isoamyl alcohol with diethyl ether and shake up, an
overhead layer is painted in the dark blue colour as a result of transition in alcohol-ether layer of
chrome peroxide (perchromic acid).
Cations reactions
15
Reactions of tin(II) cations detection:
1. Action of sodium or potassium hydroxide. Hydroxides of alkaline metals with tin(ІІ) salts forms
white precipitate, soluble in surplus of alkali and acids :
SnCl2 + 2NaOH = ↓Sn(OH)2 + 2NaCl
Sn(OH)2 + 2NaОН = Na2SnO2 + 2Н2О
Sn(OH)2 + 2НCl = SnCl2 + 2H2O
In case in presence of hydrogen peroxide the sodium stannite across to sodium stannate:
Na2SnO2 + Н2О2 = Na2SnO3 + Н2О
2. Action of ammonium hydroxide. Ammonium hydroxide with Sn+2 ions forms white precipitate,
insoluble in surplus of reagent:
SnCl2 + 2NН4OH = ↓Sn(OH)2 + 2NН4Cl
3. Action of hydrogen sulphide, solubility of sulphides. Hydrogen sulphide or ammonium sulphide
with solutions of tin(ІІ) salts form dark-brown precipitate:
SnCl2 + H2S = ↓SnS + 2HCl
SnS precipitate is insoluble in alkalis and in surplus of sodium sulphide, but easily dissolves in
ammonium polysulphide with thio-salts formation:
SnS + (NH4)2S2 = SnS2 +(NH4)2S
SnS2 +(NH4)2S2 = (NH4)2SnS3 +S
4. Action of salts of bismuth(III) and mercury(ІІ) in alkaline environment. Tin(II) easily enter to
oxidation-reducing reaction as reducer. Typical is oxidising-reducing reaction with salts of
bismuth(III) and mercury(II) in the alkaline environment. As a result of reactions the
precipitations of element mercury and bismuth sediment:
SnСl2 + 4NaОН = Na2SnO2 + 2Н2О+ 2NaCl
Na2SnO2 + 2НgCl2+ 2NaOH = Na2SnO3 + ↓2Нg + 4NaCl +H2O
3Na2SnO2 + 2Bi(NO3)3+ 6NaOH = 3Na2SnO3 + ↓2Bi + 6NaNO3 +3H2O
Reactions of tin(IV) cations detection:
1. Action of sodium or potassium, or ammonium hydroxides. Hydroxides form white precipitate,
which has amphoteric properties:
H2[SnCl6]+ 6NaОН = ↓H2[Sn(OH)6] + 6NaCl
Precipitate is soluble in the alkali surplus:
H2[Sn(OH)6] + 2NaОН = Na2[Sn(OH)6] + 2Н2O.
In acids the precipitate dissolves with formation of complex salts:
Cations reactions
16
H2[Sn(OH)6] + 6НCl = H2[SnCl6] + 6Н2O.
2. Action of hydrogen sulphide. With the hydrogen sulphide the tin(IV) salt forms yellow
precipitate:
H2[SnCl6] + 2H2S = ↓SnS2 + 6HCl.
Precipitate is soluble in concentrated chloride acid:
SnS2 + 6HCl = H2[SnCl6] +2H2S.
Unlike Sn+2 salts the sulphide of Sn+4 is soluble in (NH4)2S solution:
SnS2 + (NH4)2S = (NH4)2SnS3.
3. Test with metallic iron. Unlike Sn+2 Sn+4 does not proceed in ions of bismuth and mercury,
however in acidic environment is reduced by iron to Sn+2:
H2[SnCl6] + Fe = FeCl2 + SnCl2 + 2HCl
4. Action of cupferron. Cupferron (ammonium salt of N-nitrozo-phenyl-hydroxyl-amine) with
tin(IV) ions forms yellow hardly soluble compound:
NO
N
NO
4
N
O
+ H2[SnCl6] + 2NH4OH
ONH4
O
Sn
ON
O
N
NO
O
N
N
ON
+ 6 NH4Cl + 2H2O
Reactions of arsenic(III) cations detection:
1. Action of sodium hypophosphite. Sodium hypophosphite in acidic environment reduces
compounds of arsenic(III) and arsenic(V) to free arsenic, which forms sediment of brown colour
or paints solution in the brown colour:
NaH2PO2 + HCl = NaCl + H3PO2
As2O3 + 3H3PO2 = ↓2As + H3PO3
2. Action of sodium hydroxide and hydrogen peroxide. In alkaline environment under action of
hydrogen peroxide As+3 transforms to As+5:
Na3AsO3 + H2O2 = Na3AsO4 + H2O
Cations reactions
17
3. Action of sulphides. The sulphides in strong acidic environment with arsenic salts form yellow
precipitate:
2Na3AsO3 + 3H2S + 6HCl = ↓As2S3 + 6NaCl + 3H2O
Arsenic sulphide is soluble in solutions of sodium hydroxide, sodium sulphide, ammonium
polysulphide, and ammonium carbonate and insoluble in concentrated chloride acid:
As2S3 + 6NaOH = Na3AsS3 + Na3AsO3 + 3H2O
As2S3 + 3Na2S = 2Na3AsS3
As2S3 + 3(NH4)2S2 = 2(NH4)3AsS4 +S
As2S3 + 3(NH4)2CO3 = (NH4)3AsS3 + (NH4)3AsO3 + 3CO2
4. Action of silver nitrate. In neutral or alkaline environment silver nitrate with anion AsO3–3
forms yellow precipitate:
Na3AsO3 + 3AgNO3 = ↓3Ag3AsO3 + 3Na NO3
Precipitate is soluble in solutions of nitric and acetic acids, and also in solution of ammonium
hydroxide.
5. Action of iodine solution. In weak alkali environment under act of free iodine AsO3–3 ions
transforms in AsO3–4, discolouring thus iodine solution:
Na3AsO3 + I2 + 2NaHCO3 = Na3AsO4 + 2NaI + 2CO2 + H2O
6. The Marsh’s test. The very small quantities of arsenic (< 0,1 mg) are well detected as arsine
AsH3, which get after reducing of arsenic:
2Na3AsO3 + 6Zn + 9H2SO4 = ↑2AsH3 +6ZnSO4 + 3Na2SO4 +6H2O
Formed colourless arsine decomposes at heating with formation of free arsenic:
2AsH3 = ↓2As + 3H2
7. The Gutzeit’s test. Formed after presented highly reactions arsine forms with silver nitrate
yellow complex, which decomposes under action of moisture to metallic silver:
AsH3 + AgNO3 = [AsAg6(NO3)3] + 3HNO3
[AsAg6(NO3)3] + 3H2O = H3AsO3 + ↓6Ag + 3HNO3
– For the AsH3 detection use a paper, saturated by alcoholic solution of HgCl2. In this case vapour
of arsine form orange or yellow colouring:
AsH3 + 3HgCl 2 = As(HgCl)3 + 3HCl
– It is possible also to detect the AsH3 presence in case of his admission through pipe with the
crystalline iodine. Thus forms arsenic iodide having red colour:
AsH3 + 3І2 = AsІ3 + 3HІ
Cations reactions
18
Reactions of arsenic(V) cations detection:
1. Action of sodium hypophosphite. Sodium hypophosphite in acidic environment reduces
arsenic(III) and arsenic(V) to free arsenic, which forms sediment of brown colour or paints
solution in the brown colour:
NaH2PO2 + HCl = NaCl + H3PO2
As2O5 + 5H3PO2 = ↓2As + 5H3PO3
2. Action of sulphides. Sulphides in strong acidic environment with arsenic salts form yellow
precipitate:
2Na3AsO4 + 5H2S + 6HCl = ↓As2S5 + 6NaCl + 3H2O
The arsenic sulphide is soluble in solutions of sodium of hydroxide, sodium sulphide, ammonium
polysulphide, and ammonium carbonate:
As2S5 + 6NaOH = Na3AsS4 + Na3AsO3S + 3H2O
As2S5 + 3Na2S = 2Na3AsS3 + 2S
As2S5 + 3(NH4)2S2 = 2(NH4)3AsS4 +3S
As2S5 + 3(NH4)2CO3 = (NH4)3AsS4 + (NH4)3AsO3S + 3CO2
3. Action of silver nitrate. In the neutral or alkaline environment silver nitrate with anion AsO4–3
forms precipitate of chocolate colour:
Na3AsO4 + 3AgNO3 = ↓3Ag3AsO4 + 3Na NO3
Precipitate is soluble in solutions of nitric and acetic acids, and in solution of ammonium hydroxide.
4. Action of potassium iodide. Potassium iodide in acidic environment reduces AsO4–3 to AsO3–3,
the brown colouring of free iodine thus appears:
Na3AsO4 + 2КI + 2HCl = Na3AsO3 + I2 + 2KCl + H2O
5. Action of magnesial mixture. Magnesial mixture with arsenate-ions forms white crystalline
precipitate, soluble in chloride acid:
Na2HAsO4 + MgCl2 + NH4OH = ↓MgNH4AsO4 + 2NaCl + H2O
6. Action of molybdenum liquid. In acidic environment ammonium molybdate with arsenate-ions
forms yellow precipitate:
12(NH4)2 MoO4 + (NH4)3AsO4 + 24HNO3 = ↓(NH4)3AsO4·12MoO3 + 24NH4NO3 + 10H2O
7. The Marsh’s test. The very small quantities of arsenic (< 0,1 mg) are well detected as arsine
AsH3, which get after reducing of arsenic:
2Na3AsO4 + 8Zn + 11H2SO4 = ↑2AsH3 +8ZnSO4 + 3Na2SO4 +8H2O
Formed colourless arsine decomposes at heating with formation of free arsenic:
2AsH3 = ↓2As + 3H2
Reactions of arsine detection are presented among reactions of arsenic (III).
Cations reactions
19
Reactions of Detection of the Fifth Analytical Group Cations
Reactions of magnesium cations detection:
1. Action of ammonium and sodium hydroxide. Ammonium and sodium hydroxide with cations to
magnesium form white amorphous precipitate, soluble in acids and salts of ammonium:
MgCl2 + 2NaOH = Mg(OH)2↓ + 2NaCl
2. Action of sodium monohydrogenphosphate. Sodium hydrogenphosphate in presence of the
chloride ammonium and ammonium hydroxide with magnesium salts forms white crystalline
precipitate:
MgCl2 + Na2HPO4 + NH4OH = MgNH4PO4↓ + 2NaCl + H2O
Precipitate is soluble in the strong acids and acetic acid:
MgNH4PO4 + 3HCl = H3PO4 + MgCl2 + NH4Cl
MgNH4PO4 + 2CH3COOH = Mg(CH3COO)2 + NH4H2PO4
3. Action of 8-oxyquinolone (luminescence test). 8-oxyquinoline with magnesium ions to at рН 912 forms oxyquinolate fluorescing by the green colour:
OH
N
N
2
O
+ Mg(OH)2
Mg
O
+ 2H2O
N
The reaction is performed on filtration paper.
4. Action of magnesone-І and magnesone-ІІ. Magnezone-І (p-nitrobenzenazoresorzinole) and
magnesone-ІІ (p-nitrobenzenazonaphthole) in the alkaline environment adsorb on Mg(OH)2
precipitate, changing thus red-violet colour on dark blue:
5.
HO + HO-Mg-OH
O2N
N N
OH
HO
O2N
Mg
N N
O
OH + H2O
Magnesone-І
Cations reactions
20
HO + HO-Mg-OH
O2N
O2N
N N
Mg
HO
O
+ H2O
N N
Magnesone-ІІ
Reactions of iron(II) cations detection:
1. Action of ammonium hydroxide and sodium hydroxide. Ammonium hydroxide and sodium
hydroxide with the iron(ІІ) ions form amorphous grey-green precipitate, soluble in acids:
FeSO4 + 2NaOH = Fe(OH)2 ↓+ Na2SO4
The precipitate quickly oxidises on air, changing colour to red-brown.
2. Action of ammonium sulphide. Ammonium sulphide with the iron(ІІ) salts forms black
precipitate, soluble in diluted mineral acids:
FeSO4 + (NH4)2S = FeS↓ + (NH4)2SO4
3. Action of potassium hexacyanoferrate(III). Potassium hexacyanoferrate(ІІІ) with the iron(ІІ)
salts forms dark blue precipitate:
3FeSO4 + 2K3[Fe(CN)6] = Fe3[Fe(CN)6]2↓ + 3K2SO4
The precipitate does not dissolve in acids, but decomposes by alkalis. The reaction is specific.
4. Action of dimethylglioxime. Diacethyldioxime in the ammonium environment with the iron(ІІ)
ions forms soluble complex halving red colour :
OH
H3C
C
N-OH
H3C
C
H3C
C
N-OH
C
CH3
+ H2SO4
Fe
+ FeSO4
2
N
N-O
H3C
C
N
O-N
C
CH3
OH
5. Action of dipyridile. 2,2-dipyridile or o-phenanthroline in acidic environment with the iron(ІІ)
ions forms inner-complex compound halving crimson colour:
Cations reactions
21
N
N
+ FeSO4
2
N
N
Fe
N
SO4
N
6. Action of oxidants (KMnO4, І2). Oxidants in acidic environment oxidise the iron(ІІ) ion to
iron(ІІІ) ion:
10FeSO4 + 2KMnO4 + 8H2SO4 = 5Fe2(SO4)3 + 2MnSO4 + K2SO4 + 8H2O
2FeSO4 + I2 + H2SO4 = Fe2(SO4)3 + 2HI
Colour of oxidisers – crimson of potassium permanganate or yellow of iodine – disappear.
Reactions of iron(III) cations detection:
1. Action of ammonium hydroxide and sodium hydroxide. Ammonium hydroxide and sodium
hydroxide with the iron(ІІІ) ions form amorphous red-brown precipitate, soluble in acids and
insoluble in alkali surplus:
FeCl3 + 3NaOH = Fe(OH)3↓ + 3NaCl
3. Action of sodium sulphide. Sodium sulphide with solutions of iron(ІІІ) salts forms black
precipitate, soluble in mineral acids:
2FeCl3 + 3Na2S = Fe2S3↓ + 3NaCl
4. Action of potassium hexacyanoferrate(ІІ). Potassium hexacyanoferrate(ІІ) in slightly acidic
environment with the iron(ІІІ) salts forms navy precipitate of “Berlin blue”:
4FeCl3 + 3K4[Fe(CN)6] = Fe4[Fe(CN)6]3↓ + 12KCl
The precipitate does not dissolve in the mineral acids, but soluble in solution of oxalic acid with the
complex formation. The reaction is specific.
5. Action of thiocyanates. Potassium or ammonium thiocyanate in slightly acidic environment
with the iron(ІІІ) salts form the complex halving bloody-red colour:
FeCl3 + 3KSCN = Fe(SCN)3 + 3KCl
6. Action of sodium acetate. Sodium acetate with the iron(ІІІ) ions at cold forms iron(ІІІ) acetate
with red-brown colour:
FeCl3 + 3CH3COONa = Fe(CH3COO)3 + 3NaCl
Cations reactions
22
If to dilute solution by water and to boil, the formed compound hydrolyses with formation of basic
salt, which falls as brown precipitate:
Fe(CH3COO)3 + 2H2O = Fe(OH)2(CH3COO)↓ +2CH3COOH
7. Action of potassium iodide. Potassium iodide reduces the iron(ІІІ) ions to the iron(II) ions. As a
result of reaction an iodine forms and solution changes colour to brown:
2FeCl3 + 2KI = 2FeCl2 + I2 + 2KCl
If to the test-tube add few drops of benzene or chloroform and shake mixture, the iodine will pass to
organic solvent and change colour of organic phase on violet.
8. Action of sulphosalicylic acid. Sulphosalicylic acid in acidic solutions (рН 1,8 – 2,5) with the
iron(ІІІ) ions forms stabile complex with red-violet colour:
COO
COOH
HO
HO
Fe
+ FeCl3
SO3H
OH + HCl
SO3
At the indicated acidity the reaction is specific for iron(ІІІ) ions.
Reactions of manganese(II) cations detection:
1. Action of sodium hydroxide and ammonium hydroxide. Hydroxides of alkaline metals and
ammonium hydroxide precipitate from solutions of manganese(ІІ) salts the white precipitate
Mn(OH)2, which changes to brown on air as a result of oxidisation by air oxygen to MnО(OH)2:
MnSO4 + 2NaOH = Mn(OH)2↓ + Na2SO4
2Mn(OH)2 + H2O +O2 = 2Mn(OH)4
Mn(OH)4 = MnO(OH)2 + H2O
Precipitate is insoluble in alkalis, soluble in acids.
2. Action of ammonium sulphide. Ammonium sulphide with manganese(ІІ) cations forms lightbrown precipitate:
MnSO4 + (NH4)2S = MnS↓ + (NH4)2SO4
Precipitate is soluble in diluted mineral acids.
3. Action of oxidants. Oxidants in acidic environment oxidise the manganese(ІІ) cation to MnO4–
anion, which in solutions has the character raspberry (crimcon) colour:
– ammonium persulphate:
2MnSO4 + 5(NH4)2S2O8 + 8H2O = 2HMnO4 + 5(NH4)2SO4 + 7H2SO4
Cations reactions
23
A reaction is performed at heating in presence AgNO3 catalyst.
– lead dioxide:
2MnSO4 + 5PbO2 + 6HNO3 = 2HMnO4 + 2PbSO4 + 3 Pb(NO3)2 + 2H2O
– sodium bismuthate:
2Mn(NO3)2 + 5NaBiO3+ 16HNO3 = 2HMnO4 + 5Bi(NO3)3 + 5NaNO3 + 7H2O
Reactions of bismuth cations detection:
1. Action of sodium hydroxide and ammonium hydroxide. The alkalis form white precipitate of
bismuth hydroxide, which dissolves in acids and does not dissolve in alkalis:
BiCl3 + 3NaOH = Bi(OH)3↓ + 3NaCl
The bismuth hydroxide at boiling transfers to yellow bismuthyl hydroxide BiО(OH).
2. Action of sodium sulphide. Sodium sulphide in acidic environment with the bismuth(ІІІ) salts
gives brown-black precipitate:
BiCl3 + 3Na2S= Bi2S3↓ + 6NaCl
Precipitate is insoluble in the diluted acids, except concentrated nitrate acid:
Bi2S3 + 8НNO3 = 2Bi(NO3)3 + 2NO↑ + 3S↓ + 4Н2О
3. Action of thiourea and sodium fluoride. Bismuth ions with thiourea forms various complexes
with yellow colour:
NH2
Bi(NO3)3 + 9 S
C
NH2
Bi S
NH2
(NO3)3
C
NH2 9
4. Action of potassium iodide. Potassium iodide precipitates from solutions of bismuth salts black
precipitate BiI3, soluble in surplus of reagent with formation of yellow complex:
BiCl3 + 3KI = BiI3↓ + 3KCl
BiI3 + KI = К[BiI4]
5. Action of sodium stannite. Reducers (SnCl2) reduce ions of bismuth(ІІІ) to metallic bismuth,
which falls as black precipitate:
SnCl2 + 4NaOH = Na2SnO2 + 2NaCl + 2H2O
Bi(NO3)3 + 3NaOH = Bi(OH)3↓ + 3NaNO3
2Bi(OH)3 + 3Na2SnO2 = 3Na2SnO3 + 2Bi↓ + 3H2O
Cations reactions
24
6. Hydrolysis of bismuth salts. In case of dilution of bismuth salts solutions occurs hydrolysis with
formation of compounds of bismuth(ІІІ) oxide (bismuthyl) BiO+ having white colour :
BiCl3 + 2H2O = Bi(OH)2Cl↓ + 2HCl
Bi(OH)2Cl = BiOCl↓ + H2O
Precipitate is soluble in mineral acids and insoluble in tartaric acid.
Reactions of antimony(III) [stibium(III)] cations detection:
1. Action to sodium hydroxide and ammonium hydroxide. Alkalis and ammonium hydroxide with
salts of antimony(ІІІ) form white precipitate:
SbCl3 + 3NaOH = Sb(OH)3↓ + 3NaCl
Fresh precipitate is soluble in alkalis with formation Na[Sb(OH)4] complex, and also in strong acids
with formation of the proper salts.
2. Action of hydrogen sulphide. Hydrogen sulphide with salts of antimony(ІІІ) in acidic
environment forms orange-red precipitate:
2SbCl3 + 3Na2S = Sb2S3↓ + 6NaCl
Precipitate is soluble at heating in Na2S surplus with formation of thiosalts and also in solutions of
alkalis:
Sb2S3 + 3Na2S = 2Na3SbS3
Sb2S3 + 4NaOH = Na[Sb(OH)4] + Na3SbS3
3. Action of metals. Cations of antimony in acidic environment reduces by metals, which are more
active electrochemically – zinc, tin, iron, aluminium; the metallic plate thus turns black:
2SbCl3 + 3Zn = 2Sb↓ + 3ZnCl2
4. Hydrolysis of antimony (III) salts. Salts of antimony(ІІІ) in slightly acidic solutions hydrolyse
forming salts of antimony(ІІІ) oxide (antimonyl) SbO– white colour:
SbCl3 + Н2O = SbOCl↓ + 2НCl
5. Reaction with rhodamine B. Rhodamine B and other basic triphenylmethane dyes (methyl
violet, diamond green) in chloride acid solution with chloride complex of antimony(V) form
ionic associate insoluble in water and painted in violet colour:
+
(C2H5)2N
O
_
N (C2H5)2Cl
+ H[SbCl6]
COOH
Cations reactions
25
+
(C2H5)2N
O
N (C2H5)2
. [SbCl ]
6
_
+ HCl
COOH
The complex extracts by benzene and iso-propanole. For transformation of antimony(ІІІ) in
antimony(V) add concentrated chloride acid and sodium nitrite.
Reactions of antimony(V) cations detection:
1. Action of sodium hydroxide and ammonium hydroxide. Alkalis and ammonium hydroxide with
salts of antimony(V) form white precipitate:
H[SbCl6] + 6NaOH = SbO(OH)3↓ + 6NaCl + 2H2O
Precipitate is soluble in strong acids:
SbO(OH)3 + 6HCl = H[SbCl6] +4H2O
2. Action of hydrogen sulphide. Hydrogen sulphide with salts of antimony(V) in acidic
environment forms orange-red precipitate:
2H[SbCl6] + 5Н2S = Sb2S5↓ + 12НCl
Precipitate is soluble at heating in Na2S surplus with formation of thiosalts, and in solutions of
alkalis:
Sb2S5 + 3Na2S = 2Na3SbS4
4Sb2S5 + 18NaOH = 3Na[Sb(OH)6] + 5Na3SbS4
3. Action of metals. Cations of antimony in acidic environment reduce by electrochemically more
active metals (zinc, tin, iron, aluminium) to free antimony; the metallic plate thus turns black:
2H[SbCl6] + 5Zn = 2Sb↓ + 5ZnCl2 + 2HCl
4. Hydrolysis of antimony(V) salts. At hydrolysis of salts of antimony(V) forms white precipitate
of basic salt of antimony(V), soluble in surplus of chloride acid:
H[SbCl6] + 2H2O = ↓SbO2Cl + 5HCl
5. Reaction with rhodamine B. Rhodamine B and other basic triphenylmethane dyes (methyl
violet, diamond green) in chloride acid solution with chloride complex of antimony(V) form
insoluble in water, painted in the violet colour ionic associate:
Cations reactions
26
_
+
(C2H5)2N
N (C2H5)2Cl
O
+ H[SbCl6]
COOH
+
(C2H5)2N
N (C2H5)2
O
. [SbCl ]
6
_
+ HCl
COOH
The complex well extracts by benzene and iso-propanole.
Cations reactions
27
Reactions of the Sixth Analytical Group Cations Detection
Reactions of cadmium cations detection:
1. Action of ammonium hydroxide and sodium hydroxide. Ammonium hydroxide in equivalent
quantities and sodium hydroxide with solutions of cadmium salts form white precipitate,
insoluble in alkalis, soluble in acids and ammonia solutions with formation of colourless
complex of tetraammin-cadmium-ion:
CdCl2 + 2NH4OH = Cd(OH)2↓+ 2NH4Cl
Cd(OH)2 + 4NH3 = [Cd(NH3)4](OH)2
2. Action of sodium sulphide. Hydrogen sulphide or sulphides of alkaline metals at рН ~ 0,5 with
cadmium ions form yellow precipitate, insoluble in solution of sodium sulphide and sodium
hydroxide, soluble in concentrated chloride and nitrate acids:
CdCl2 + H2S = CdS↓ + 2HCl
CdS + 4HCl = H2[CdCl4] + H2S
CdS + 4HNO3 = Cd(NO3)2 + S↓ + 2NO2↑ + 2H2O
CdS + H2SO4 = CdSO4 + H2S↑
3. Action of sodium hydrogen phosphate. Sodium hydrogen phosphate forms white precipitate,
soluble in acetic and mineral acids:
3Cd(NO3)2 + 4Na2HPO4 = Cd3(PO4)2↓ + 2NaH2PO4 + 6NaNO3
4. Action of ammoniumperchlorate. Ammonium perchlorate in ammonium solutions of cadmium
salts forms white precipitate:
Cd(NO3)2 + 2NH4ClO4 + 4NH3 = Cd[(NH3)4](ClO4)↓2 + 2NH4NO3
5. Action of dithizone. Dithizone interacts with cadmium ions in interval pН 6,5-14 with formation
of red inner-complex compound, which can be extracted by chloroform or carbon tetrachloride:
NH
N
C
2
N
N
NH
N
N
C
N
Cations reactions
SH + Cd(NO3)2
N
S
Cd
S
N
C
+ 2HNO3
N
NH
28
Reactions of cobalt(II) cations detection:
1. Action of ammonium hydroxide. Ammonium hydroxide precipitates from solutions of cobalt
salts dark blue precipitate of basic salt, soluble in the reagent surplus with formation of yellow
complex of hexaamminecobalt(ІІ):
CoCl2 + NH3 + H2O = CoOHCl↓ + NH4Cl
CoOHCl + NH3 + NH4Cl = Co[(NH3)6]Cl2 +H2O
The chloride of hexaamminecobalt(ІІ) under act of air oxygen gradually passes to the chloride of
pentaamminecobalt(ІІІ) Co[(NH3)5Cl]Cl2 red colour. This reaction passes instantly under act of
H2 O2 .
2. Action of sodium hydroxide. The alkalis form with the cobalt(ІІ) ions dark blue precipitate of
basic salt CoOHCl:
CoCl2 + NаOН = CoOHCl↓ + NаCl
In case of further addition of alkali and heating the precipitate transforms to cobalt(ІІ) hydroxide
rose colour:
CoОНCl + NаOН = Co(OH)2↓ + NаCl
On air Co(OH)2 precipitate gradually change colour to brown, transforming to cobalt(III)
hydroxide.
3. Action of sodium sulphide. Sulphides form black precipitate, soluble in mineral acids:
CoCl2 + Nа2S = CoS↓ + 2NаCl
4. Action of thiocyanates. Ammonium thiocynate in presence an amyl alcohol with the cobalt salts
forms dark-blue complex, which passes to layer of organic solvent:
CoCl2 + 4NH4SCN = (NH4)2[Co(SCN)4] + 2NH4Cl
5. Action of ammonium tetrathiocyanomercurate(II). Ammonium tetrathiocyanomercurate(II) with
the cobalt ions forms blue complex:
2(NH4)2[Hg(SCN)4] + CoSO4 = Co[Hg(SCN)4]↓ + 2(NH4)2SO4
This reagent in presence of zinc salts forms double salt of cobalt-zinc tetrathiocyanomercurate(II)
having navy colour:
2(NH4)2[Hg(SCN)4] + CoSO4 + ZnSO4 = Zn[Hg(SCN)4]·Co[Hg(SCN)4]↓ + 2(NH4)2SO4
6. Action of α-nitroso-β-naphthole. α-nitroso-β-naphthole with the cobalt(ІІІ) ions forms redbrown precipitate, soluble in organic solvents – chloroform and benzene. The oxidization of
cobalt(ІІ) to cobalt(ІІІ) takes place in acidic environment under action of hydrogen peroxide:
N-OH
NO
OH
Cations reactions
O
29
N-OH
N
O
3
O O
N
Co
+ Co(NO3)2 + H2O2 + HNO3
O
O
O
+ 3HNO3 + 2H2O
O
N
7. Reaction of “Rinmann’s green” formation. After burning a piece of filtration paper, moistened
by solution of zinc and cobalt nitrate, get an ash, painted in green colour of cobalt zincate:
Zn(NO3)2 + Co(NO3)2 = CoZnO2 + 4NO2↑ + O2↑
Reactions of copper(II) cations detection:
1. Action of ammonium hydroxide. At first ammonium hydroxide from solutions of copper(ІІ) salts
forms blue-green precipitate of basic salts of copper, which dissolves in the reagent surplus with
formation of intensive navy complex:
CuSO4 + 2NH4OH = (CuOH)2SO4↓ + (NH4)2SO4
(CuOH)2SO4 + (NH4)2SO4 +6NH3 = 2[Cu(NH3)4]SO4 + 2H2O
In case of acidifying the ammonium complex of copper destroys as a result of exchange of
ammonium molecules to Н+ ions with formation of more stable NH4+ complex. The navy colour of
solution thus changes on blue.
2. Action to sodium hydroxide. Hydroxides of alkaline metals with copper(ІІ) ions forms blue
precipitate, which in case of heating loses water and transfers to black oxide:
CuSO4 + 2NаOH = Cu(OH)2↓ + 2Nа2SO4
Cu(OH)2 = ↓CuO + Н2O
Cu(OH)2 soluble in the ammonia solutions and organic acids (tartaric, citric) with complexes
formation. In concentrated solutions of alkalis Cu(OH)2 dissolves, forming cuprites Na2CuO2.
3. Reducing reaction. The reaction of copper(ІІ) ions reducing to elemental copper can be carried
out by more active metals (iron, zinc, aluminium):
CuSO4 + Zn = Cu↓ + ZnSO4
An acidified by sulphate or chloride acid solution of copper salt places on metallic plate. On the
plate appears red spot of free copper.
Cations reactions
30
4. Action of potassium hexacyanoferrate(ІІ). Potassium hexacyanoferrate(ІІ) with the copper salts
forms red-brown precipitate, insoluble in diluted acids:
2CuSO4 + K4[Fe(CN)6] = Сu2[Fe(CN)6]↓ + 2K2SO4
5. Action of cuprone (α−benzoynoxime). Cuprone with the copper(ІІ) ions forms insoluble darkgreen complex:
CH
+ CuSO4
CH
N
OH
HO
CH
CH
O
N
O
+ H2SO4
Cu
6. Flame test. Salts of copper(ІІ) paint colourless flame in dark blue or green colour.
Reactions of nickel cations detection:
1. Action of ammonium hydroxide. Ammonium hydroxide from solutions of nickel(II) salts
precipitates green precipitate of basic salt of nickel(ІІ), soluble in surplus of reagent with
formation of indigo blue complex:
Ni(NO3)2 + NH3+ H2O = NiOHNO3↓ + NH4NO3
NiOHNO3 + NH4NO3 + 5NH3 = [Ni(NH3)6](NO3)2 + H2O
2. Action of sodium hydroxide. Alkalis with nickel(II) ions form soluble in acids green precipitate:
NiSO4 + 2NaOH = Ni(OH)2↓ + Na2SO4
3. Action of sodium monhydrogenphosphate. Sodium hydrogenphosphate with nickel(II) cations
forms green precipitate:
3Ni(NO3)2 + 4Na2HPO4 = Ni3(PO4)2↓ + 2NaH2PO4 + 6NaNO3
4. Action of diacetyl dioxime. Diacetyl dioxime with nickel ions forms inner-complex compound
halving red colour:
OH
H3C
C
N-OH
H3C
C
H3C
C
N-OH
C
CH3
+ H2SO4
Ni
+ NiSO4
2
N
N-O
H3C
C
N
O-N
C
CH3
OH
The reaction performs on filtration paper and uses for fractional method.
Cations reactions
31
Reactions of mercury cations detection:
1. Action of ammonium hydroxide. Ammonia solution from water solutions of mercury(II) salts
precipitates white precipitate, soluble in the reagent surplus with formation of colourless
complex:
HgCl2 + 2NH3 = HgNH2Cl↓ + NH4Cl
HgNH2Cl + NH4Cl + 2NH3 = [Hg(NH3)4]Cl2
2. Action of sodium hydroxide. Hydroxides of alkaline metals from water solutions of mercury(II)
salts precipitate yellow precipitate:
HgCl2 + 2NaOH = HgO↓ + 2NaCl + H2O
3. Action of iodides. Potassium iodide with mercury(II) cations forms brightly red precipitate,
soluble in surplus of reagent with formation of the colourless complex:
HgCl2 + 2KI = HgI2↓ + 2KCl
HgI2 + 2KI = K2[HgI4]
The reaction goes in weak acidic environment. The reaction with iodides uses for mercury(II)
cations detection by drops technique in presence of all another cations: the red spot of HgI2 forms in
the centre of filter paper.
4. Action of sulphides. Solubility of sulphides. Sodium sulphide from solutions of mercury(II) salts
precipitates brown-black precipitate:
HgCl2 + Na2S = HgS↓ + 2NaCl
Precipitate is insoluble in chloride and nitrate acids, but soluble in mixture of this acids (“aqua
regia”):
3HgS + 2HNO3 + 12HCl = 3H2[HgCl4] + 3S↓ + 2NO↑ + 4H2O
5. Action of reducers. Reducers (SnCl2, Cu) proceed mercury(II) cations to mercury(І) cations, and
then to the free mercury. In solutions or on filtration paper in case of interaction of mercury salts
with tin(II) chloride appears black precipitate of free mercury:
HgCl2 + SnCl2 = Hg2Cl2↓ + SnCl4
Hg2Cl2 + SnCl2 = 2Hg↓ + SnCl4
If on copper plate to place a drop of mercury(II) salt solution, on plate through 4-5 min. will appear
black precipitate of free mercury:
HgCl2 + Cu = Hg↓ + CuCl2
In case of the spot rubbing a brilliant plaque of copper amalgam appears.
6. Action of diphenylcarbaside. Diphenylcarbaside with mercury(II) salts in itrate acid environment
forms dark blue or violet complex:
Cations reactions
32
NH-N
2
C-OH + Hg(NO3)2
NH-NH
NH
NH-NH
N
C-O
NH-NH
Cations reactions
Hg
+ 2HNO3
O-C
N
NH
33