Pharmaceutical Analytical Chemistry I Lecture 7 PDF

Lecture (7) Dr. Ahmed Abdel-Monem  Cations of group (IV) - Name of group: Zinc gp. or ammonium sulphide gp. - Contains : Zinc Zn2+ Manganese Mn2+ Cobalt Co2+ Nickel Ni2+ Pptd. as : Sulphide...

Lecture (7) Dr. Ahmed Abdel-Monem  Cations of group (IV) - Name of group: Zinc gp. or ammonium sulphide gp. - Contains : Zinc Zn2+ Manganese Mn2+ Cobalt Co2+ Nickel Ni2+ Pptd. as : Sulphide - ZnS  white ppt. - MnS  buff ppt. - CoS  black ppt. - NiS  black ppt. Group reagent : H2S in presence of NH4OH and NH4Cl - Precipitation : - To filtrate from gp. III, add NH4Cl ( & NH4OH "till the solution alkaline". - Boil + add H2S till complete pptn. - Boil till no NH3 odour and filter ppt of gp. IV as sulphide Filtrate wash with 1% NH4Cl gp. V – VI containing little (NH4)2S and filter ppt. as Filtrate ZnS, MnS, CoS & NiS reject Sky blue ppt * Identification and Confirmation of Co2+ : - Vogel’s reaction: soln. + conc. HCl + solid of NH4CNS + 1 ml of ether (or amyl shake alcohol)  blue colour in the etherial layer or alcoholic layer. Heating at 60 C is done because: (1) To convert any soluble bicarbonate of gp. V into insoluble carbonate (2) Promotes pptn. of the carbonates when the ions are present at low concentration. (3) Formation of a more crystalline ppt. Separation: The separation is based upon : 1- BaCrO4 is insoluble in dil. acetic acid while SrCrO4 and CaCrO4 are soluble in acetic acid 2- Sr2+ can be pptd. by saturated soln. of (NH4)2S4 in faintly ammoniacal solution while CaSO4 is soluble. THANK YOU