The optimum pH range is between 7 and 10. , Dichlorofluorescein For chlorides, bromides, and iodides and thicyanate Stronger acid and may be utilised in slightly acid solution of pH greater than 4.4. Eosin bromides, and iodides and thicyanate (NOT FOR Cl-) Stronger acid and can used down to a pH of 1.2. The colour change is sharpest in an acetic acid d- Turbidity method: Liebig's method for cyanides. When a solution of silver nitrate is added to a solution containing cyanide ions (e.g. alkali cyanide) a white precipitate is first formed, but on stirring it re-dissolves owing to the formation of soluble stable complex cyanide, AgNO3 + 2 KCN KAg(CN)2 + KNO3 → or Ag+ + 2 CN− —— [Ag(CN)2] − When the above reaction is complete, further addition of silver nitrate solution yields the insoluble silver argento cyanide. −→ Ag+ + [Ag(CN)2] Ag[Ag(CN)2] The end point of the reaction is therefore indicated by the formation of permanent turbidity. In Denige's modification of Liebig method, iodide ion is used as indicator and aqueous ammonia is introduced to solubilise the silver cyanide: Ag[Ag(CN)2] + 4NH3 —— 2 [Ag(NH3)2]+ + 2CN− The iodide ion and ammonia solution are before the titration, the formation of silver iodide (as turbidity) will indicate the end point. [Ag(NH3)2]+ + I− Agl + 2NH3 →
The optimum pH range is between 7 and 10. , Dichlorofluorescein For chlorides, bromides, and iodides and thicyanate Stronger acid and may be utilised in slightly acid solution of pH greater than 4.4. Eosin bromides, and iodides and thicyanate (NOT FOR Cl-) Stronger acid and can used down to a pH of 1.2. The colour change is sharpest in an acetic acid d- Turbidity method: Liebig's method for cyanides. When a solution of silver nitrate is added to a solution containing cyanide ions (e.g. alkali cyanide) a white precipitate is first formed, but on stirring it re-dissolves owing to the formation of soluble stable complex cyanide, AgNO3 + 2 KCN → KAg(CN)2 + KNO3 or Ag+ + 2 CN− —— [Ag(CN)2] − When the above reaction is complete, further addition of silver nitrate solution yields the insoluble silver argento cyanide. Ag+ + [Ag(CN)2] −→ Ag[Ag(CN)2] The end point of the reaction is therefore indicated by the formation of permanent turbidity. In Denige's modification of Liebig method, iodide ion is used as indicator and aqueous ammonia is introduced to solubilise the silver cyanide: Ag[Ag(CN)2] + 4NH3 —— 2 [Ag(NH3)2]+ + 2CN− The iodide ion and ammonia solution are before the titration, the formation of silver iodide (as turbidity) will indicate the end point. [Ag(NH3)2]+ + I− → Agl + 2NH3
part_2_colored.docx