Practical Analytical Chemistry (1) Practical (5) Faculty of Pharmacy Department of Pharmaceutical Chemistry

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

Anions are classified by 2 different modes: A.according to the identification by the volatile products obtained on treatment with acids. 1. Gases evolved with dil. HCl or H 2 SO 4 2. Gases or vapors evolved with conc. H 2 SO 4 3. Miscellaneous group A.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 Reagent; dilute HCl HCl Group (Group I) Conc. H 2 SO 4 (Group II) Reagents Confirmation (precipitate, colour, gas,…) conc. H 2 SO 4 Carbonates, hydrogen carbonate, sulphite, thiosulphate, sulphide, nitrite, cyanide Volatile gases Flouride, chloride, bromide, iodide, nitrate chlorate, perchlorate, bromate Permanganate, borate, ferrocyanide, ferricyanide, Thiocyanate, organic acids Colored vapours Miscellaneous Group III Sulphate phosphate

GroupAnionsReagentGases evolved Precipitates I Carbonates, hydrogen carbonate, sulphite, thiosulphate, sulphide, nitrite, cyanide Dil. HCl CO 2, SO 2, H 2 S, NO 2, HCN II Flouride, chloride, Bromide, iodide, nitrate Chlorate, perchlorate, Permanganate and organic anions conc. H 2 SO 4 HF, HCl, HBr, HI, IIISulphates and phosphatesBaCl 2 BaSO 4 Ba 3 (PO4) 2

Nitrite(NO 2 - ): is one of the most toxic environmental contaminant that causes great risks to general human health. Carbonate (CO 3 2- ), Bicarbonate (HCO 3 - ), Sulphide (S 2- ), Thiosulphate (S 2 O 3 2- ), Sulphite (SO 3 2- ), Nitrite(NO 2 - ), Cyanide(CN - ) Anions of Group I Cyanide(CN - ) : is one of the most toxic environmental contaminant that causes great risks to general human health.

Analysis of Group I Anions AnionDil HClequations CO 3 2- Effervescence due to evolution of CO 2 gas which renders lime water turbid CO H + = CO 2 ↑ + H 2 O CO 2 + Ca(OH) 2 = CaCO 3 + H 2 O HCO 3 - Effervescence due to evolution of CO 2 gas which renders lime water turbid HCO H + = CO 2 ↑ + H 2 O CO 2 + Ca(OH) 2 = CaCO 3 + H 2 O S 2- evolution of H 2 S gas characterized by its odor of bad egg which turns lead acetate paper black S H + = H 2 S ↑ H 2 S + Pb 2+ = PBS↓ black ppt NO 2 - Pale blue liquid + evolution of NO 2 brown fumes NO H + = HNO 2 ↑ + H 2 O 3HNO 2 = HNO 3 + H 2 O + 2NO 2NO ↑ + O 2 ↑ = 2NO 2 ↑ (brown)

Analysis of Group I Anions Anionph.ph. testAgNO 3 reagent CO 3 2- Pink colored solution White ppt of Ag 2 CO 3 turns dark by xss reagent CO Ag + = Ag 2 CO 3 ↓ HCO 3 - Colorless solution - Ve S 2- Black ppt of Ag 2 S↓ 2Ag + +S 2- = Ag 2 S↓ NO 2 - White crystal ppt of AgNO 2 Ag + +NO 2 - = AgNO 2 ↓

Analysis of Group I Anions AnionLead acetate reagent MgSO 4 reagent CO VeWhite ppt of MgCO 3 HCO 3 - -Ve And give +Ve result on boiling S 2- Black ppt of PbS H 2 S + Pb 2+ = PBS↓ -Ve NO 2 - -Ve

1-Write a flow chart for your unknown analysis in your lab notebook. You should include formulas of all reagents added, colors of all solutions and ppts, and conclusions made from these observations. For example, your original solution is colorless, you add HCl forming a white ppt and a colorless solution. At this point you do not know what the formula of the white ppt is, so do not write one. Points for discussion