QUALITATIVE ANALYSIS OF THE ANIONS 1 QUALITATIVE ANALYSIS OF THE ANIONS Ashraf M. Mahmoud, Associate Prof.

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

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

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

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

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.

Analysis of Group I Anions Dil HCl equations CO32- Effervescence due to evolution of CO2 gas which renders lime water turbid CO32- + 2H+ = 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 SO32- + 2H+ = SO2 ↑ + H2O SO2 + Cr2O7-2 + 2H+ = 2 Cr3+ + 3SO42- + H2O S2O32- No immediate change on cold, then (Sº) is ppt, on boilingSO2 gas volutes S2O32- + 2H+ = 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)

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 CO32- + 2Ag+ = 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 SO32- + 2Ag+ = Ag2SO3 ↓ S2O32- White ppt of BaS2O3 S2O32- + Ba2+ = BaS2O3 ↓ White ppt of Ag2SO3 turns black on standing S2O32- + 2Ag+ = Ag2S2O3 ↓ Ag2S2O3↓+H2O = Ag2S↓+ SO42- S2- Black ppt of Ag2S↓ 2Ag+ +S2- = Ag2S↓ NO2- White crystal ppt of AgNO2 Ag+ +NO2- = AgNO2↓

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-

Analysis of Group I Anions Specific tests S2- Sodium nitroprusside test Sulphide solution + KOH solution + Sodium nitroprusside → purple color is formed S2- + [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)

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-).

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 + SO42- + SO2 + H2O I- Evolution of violet vapours of I2 Which turns the starch paper paper blue I- + H2SO4 = HI ↑ + HSO4- I- + H2SO4 = I2 + SO42- + SO2 + H2O NO3- Evolution of NO2 red-brown vapours NO3- + H2SO4 = NO2↑ + H2O + O2↑ + SO42- (brown)

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

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+3 + 3 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- + Cr2O72- + 6H+ + warming → 2CrO2Cl2 ↑+ 3H2O CrO2Cl2 ↑+ 4OH- → CrO42- + 2Cl- + 2H2O Br- Chlorine water test Cl2 (dropwise)+ Br-(solution) → deep orang-red vapours of Br2 which forms orange-red Cl2 + 2Br- → Br2 + 2Cl-

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)

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.

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

Magnesia mixture reagent Analysis of Group III Anions Anion Hg (NO3)2 reagent Magnesia mixture reagent SO42- Yellow ppt of basic HgSO4 . 2HgO SO4-2 + 3Hg+2 + 2 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 ↓

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

Good Luck Ashraf M. Mahmoud