2. QUALITATIVE ANALYSIS OF THE ANIONS1
QUALITATIVE ANALYSIS
OF THE ANIONS
Ashraf M. Mahmoud, Associate Prof.

3. Why we should analyze Anions ?
What are the Anions ?
Anions are ions bearing a negative charge; they are formed from non-metallic elements due to gain of electrons.
Why we should analyze Anions ?
Some anions are necessary for human life.
Some anions are used for different pharmaceutical purposes as sulphates and carbonates.
Some anions are environmental hazards that cause great risk to human health as cyanides and nitrites.
The conc. in the body is related to the health status

4. Classification of Anions
Anions are classified by 2 different modes:
according to the identification by the volatile products obtained on treatment with acids.
1. Gases evolved with dil. HCl or H2SO4
2. Gases or vapors evolved with conc. H2SO4
3. Miscellaneous group
according to the identification by the reactions in solutions (according to their solubilities)
1. Precipitation reactions
2. oxidation-reduction reactions

5. Classification of Anions
Mixture of many Anions
Volatile gases
Reagent; dilute HCl
HCl Group
(Group I)
Conc. H2SO4
(Group II)
Miscellaneous
Group III
Sulphate phosphate
Flouride, chloride,
bromide, iodide, nitrate
chlorate, perchlorate, bromate
Permanganate, borate, ferrocyanide, ferricyanide,
Thiocyanate, organic acids
conc. H2SO4
Carbonates, hydrogen carbonate, sulphite, thiosulphate, sulphide, nitrite, cyanide
Colored vapours
Confirmation
(precipitate, colour, gas,…)
Reagents

6. Group
Anions
Reagent
Gases evolved
Precipitates I
Carbonates, hydrogen carbonate, sulphite, thiosulphate, sulphide, nitrite, cyanide
Dil. HCl
CO2, SO2, H2S, NO2, HCN II
Flouride, chloride,
Bromide, iodide, nitrate
Chlorate, perchlorate,
Permanganate and organic anions
conc. H2SO4
HF, HCl, HBr, HI,
III
Sulphates and phosphates
BaCl2
BaSO4
Ba3 (PO4)2

7. Anions of Group I
Carbonate (CO32-), Bicarbonate (HCO3-), Sulphide (S2- ) , Thiosulphate (S2O32-), Sulphite (SO32-), Nitrite(NO2-), Cyanide(CN-)
Nitrite(NO2-): is one of the most toxic environmental contaminant that causes great risks to general human health.
Cyanide(CN-) : is one of the most toxic environmental contaminant that causes great risks to general human health.

8. Analysis of Group I Anions
Dil HCl
equations
CO32-
Effervescence due to evolution of CO2 gas which renders lime water turbid
CO H+ = CO2 ↑ + H2O
CO2 + Ca(OH)2 = CaCO3 + H2O
HCO3-
HCO3- + H+ = CO2 ↑ + H2O
SO32-
evolution of SO2 gas characterized by its suffocating odor of burning (Sº) which turns acidified dichromate paper green
SO H+ = SO2 ↑ + H2O
SO2 + Cr2O H+
= 2 Cr SO42- + H2O
S2O32-
No immediate change on cold, then (Sº) is ppt, on boilingSO2 gas volutes
S2O H+ = SO2 ↑+ H2O + S↓
S2-
evolution of H2S gas characterized by its odor of bad egg which turns lead acetate paper black
S2- + 2H+ = H2S ↑
H2S + Pb2+ = PBS↓ black ppt
NO2-
Pale blue liquid + evolution of NO2 brown fumes
NO2- + H+ = HNO2 ↑ + H2O
3HNO2 = HNO3 + H2O + 2NO
2NO ↑ + O2↑ = 2NO2↑ (brown)

9. Analysis of Group I Anions
BaCl2 reagent
ph.ph. test
AgNO3 reagent
CO32-
White ppt of BaCO3
CO32- + Ba2+ = BaCO3 ↓
Pink colored solution
White ppt of Ag2CO3 turns dark by xss reagent
CO Ag+ = Ag2CO3 ↓
HCO3-
White ppt of BaCO3 on boiling
2HCO3- + Ba2+
= BaCO3 ↓+CO2 ↑ + H2O
Colorless
solution
- Ve
SO32-
White ppt of BaSO3
SO32- + Ba2+ = BaSO3 ↓
Alkaline to litmus paper
White crystal ppt of Ag2SO3 dissolve by xss reagent
SO Ag+ = Ag2SO3 ↓
S2O32-
White ppt of BaS2O3
S2O32- + Ba2+ = BaS2O3 ↓
White ppt of Ag2SO3 turns black on standing
S2O Ag+ = Ag2S2O3 ↓
Ag2S2O3↓+H2O = Ag2S↓+ SO42-
S2-
Black ppt of Ag2S↓
2Ag+ +S2- = Ag2S↓
NO2-
White crystal ppt of AgNO2
Ag+ +NO2- = AgNO2↓

10. Analysis of Group I Anions
Lead acetate
reagent
MgSO4
Iodine solution
KMnO4 + H2SO4
CO32-
-Ve
White ppt of MgCO3
HCO3-
And give +Ve result on boiling
SO32-
White ppt of PbSO3
SO32- + Pb2+ = PbSO3 ↓
Decolorization of violet color
S2O32-
White ppt of PbSO3 soluble in xss S2O32-, ppt turns black upon boiling
S2O32- + Pb2+ = PbS2O3 ↓
PbS2O3↓+H2O =PbS↓+ SO42-
Decolorization of the brown color
S2-
Black ppt of PbS
H2S + Pb2+ = PBS↓
NO2-

11. Analysis of Group I Anions
Specific tests
S2-
Sodium nitroprusside test
Sulphide solution + KOH solution + Sodium nitroprusside → purple color is formed
S [Fe(CN)5NO]2- → [Fe(CN)5NOS]4-
S2O32-
Blue ring test
S2O32- + conc. H2SO4 + ammonium molybdate (solution slowly down the side of test tube) →blue ring is formed temporarily at the contact zone
NO2-
Brown ring test
FeSO4 (25%) + dil H2SO4 or acetic acid + NO2- (solution slowly down the side of test tube) →brown ring is formed temporarily at the junction of the 2 liquids
NO2- + H+ = HNO2 ↑
3HNO2 = HNO3 + H2O + 2NO
NO ↑ + FeSO4 = [Fe, NO]SO4 (brown ring)

12. Anions of Group II
Flouride(F-), Chloride(Cl-), Bromide(Br-), Iodide(I-), Nitrate(NO3-), Chlorate(ClO3-), Perchlorate(ClO4-), Permanganate (MnO4-) and Organic anions
Nitrate(NO3-): is one of the most toxic environmental contaminant that causes great risks to general human health.
Bromide(Br-) : is one of the most toxic environmental contaminant that causes great risks to general human health.
Flouride(F-) : is one of the most important agents used in formulation of tooth paste for protecting teeth from caries.
Permanganate (MnO4-): is one of the most important agents used as antiseptic solution for wound healing.
Potassium halides are used as sedative (Br-), anti-hypokalemia (Cl-), anti-thyroid (I-), antiseptic (MnO4-).

13. Analysis of Group II Anions
Conc. H2SO4
equations F-
Evolution of colorless corrosive H2F2 gas which turns the blue litmus paper red and the test tube acquires a greasy appearance due to the action of the gas on the silica of the glass
2F- + H2SO4 = H2F2 ↑ + SO42-
H2F2 + SiO2 = SiF4 ↑ + 2H2O
3SiF4 + 3H2O = 2[SiF6]2- + H2SiO3 ↓+ 4H+
Cl-
Evolution of HCl gas with its pungent odour, turns the blue litmus paper red and forms white clouds near the mouth with NH3 paper
Cl- + H2SO4 = HCl ↑ + HSO4-
HCl + NH3 = NH4Cl
Br-
Evolution of orange-red fumes of HBr gas which changes into redish-brown fumes of bromine
Br- + H2SO4 = HBr ↑ + HSO4-
Br- + H2SO4 = Br2 + SO SO2 + H2O I-
Evolution of violet vapours of I2 Which turns the starch paper paper blue
I- + H2SO4 = HI ↑ + HSO4-
I- + H2SO4 = I2 + SO SO2 + H2O
NO3-
Evolution of NO2 red-brown vapours
NO3- + H2SO4 = NO2↑ + H2O + O2↑ + SO42- (brown)

14. Analysis of Group II Anions
AgNO3 reagent
Lead acetate reagent F- Ve
Cl-
Curdy white ppt of AgCl soluble in dil, ammonia
Cl- + Ag+ = AgCl ↓
Curdy white ppt of PbCl2 soluble in hot water
2Cl- + Pb+2 = PbCl2 ↓
Br-
Curdy pale –yellow ppt of AgBr soluble in conc. ammonia
Br- + Ag+ = AgBr ↓
White crystals of PbBr2 soluble in boiling water
2Br- + Pb+2 = PbBr2 ↓ I-
Curdy yellow ppt of AgI insoluble in conc. ammonia
I- + Ag+ = AgI ↓
Golden yellow crystals of PbI2
2I- + Pb+2 = PbI2 ↓
NO3-
- Ve

15. Analysis of Group II Anions
Specific tests F-
CaCl2 test
Slimy white ppt of CaF2 soluble in dil. HCl
2F- + Ca+2 = CaF2 ↓
Fe(Cl)3 test
White crystals of Na3[FeF6] soluble in water
6F- + Fe Na+= Na3[FeF6] ↓
Cl-
Chromyl chloride test
Cl- (solid)+ Cr2O72-(solid) + conc. H2SO4 + warming →deep red vapors of chromyl chloride gas CrO2Cl2 which form yellow solution of CrO42- on passing in NaOH solution
4Cl- + Cr2O H+ + warming → 2CrO2Cl2 ↑+ 3H2O
CrO2Cl2 ↑+ 4OH- → CrO Cl- + 2H2O
Br-
Chlorine water test
Cl2 (dropwise)+ Br-(solution) → deep orang-red vapours of Br2 which forms orange-red
Cl2 + 2Br- → Br2 + 2Cl-

16. NO ↑ + FeSO4 = [Fe, NO]SO4 (brown ring)
Analysis of Group II Anions
Anion
Specific tests
Br-
Fluorescein test
Yellow fluorescein → red eosin I-
CuSO4 test
Forms brown ppt of Cu2I2 and I2 (4I- + 2Cu+2 = Cu2I2 ↓ + I2 )
HgCl2 test
Forms scarlet-red ppt of HgI2 soluble in excess iodide
2I- + HgCl2 = HgI2↓ + 2Cl-
NO3-
Brown ring test
FeSO4 (25% saturated solution) + NO3- (solution) + conc. H2SO4 (slowly down the side of test tube) →brown ring is formed temporarily at the junction of the 2 liquids
2NO3- + 6Fe2+ +8H+ = 6Fe3+ +2NO ↑+ 4H2O
NO ↑ + FeSO4 = [Fe, NO]SO4 (brown ring)

17. Sulphates (SO42-) and Phosphates (PO43-)
Anions of Group III
Miscellaneous group
Sulphates (SO42-) and Phosphates (PO43-)
Sulphates (SO42-):
1. ferrous- sulphate, and phosphate are used as iron supplements in tonics preparations
2. Barium sulphate is used in taking barium-ray photographs of the
stomach and intestines.
3. Magnesium sulphate is used as laxative
Phosphates (PO43-) : is one of the most common electrolyte and buffers used in general human preparations.

18. Analysis of Group III Anions
AgNO3 reagent
BaCl2 reagent
Lead acetate reagent
SO42-
White crystalline ppt of Ag2SO4
SO4-2 +2Ag+ = Ag2SO4 ↓
White ppt of BaSO4 insoluble in dil HCl and HNO3
SO4-2 + Ba+2 = BaSO4 ↓
White ppt of PbSO4 soluble in conc. H2SO4 and ammonium acetate
SO4-2 + Pb+2 = PbSO4 ↓
PO43-
yellow ppt of Ag3PO4 soluble in dil, nitric acid and ammonia
PO4-3 +3Ag+ = Ag3PO4 ↓
white ppt of BaHPO4 soluble in dil, mineral acids and ammonia
HPO4-2 +Ba+2 = BaHPO4 ↓
-Ve

19. Magnesia mixture reagent
Analysis of Group III Anions
Anion
Hg (NO3)2 reagent
Magnesia mixture reagent
SO42-
Yellow ppt of basic HgSO4 . 2HgO
SO Hg H2O =
HgSO4 . 2HgO↓ + 4 H+
-Ve
PO43-
white crstalline ppt of Mg(NH4)PO4 soluble in dil, mineral acids
HPO4-2 +Mg+2 + NH3= Mg(NH4)PO4 ↓

20. Analysis of Group III Anions
Specific tests
PO43-
Ammonium molybdate test
Yellow crystalline ppt of ammonium phospho-molybdate
NH4+ + PO4-3 + H+ + MoO42- = (NH4)3PO4 + MoO3 ↓ + H2O

21. Good Luck
Ashraf M. Mahmoud