Precipitation Titration

• Volumetric Precipitimetry 


  a type of titration reaction that requires combination of ions and formation of relatively insoluble substances or precipitates to cause the reactions to go to completion and quantifiable
• Silver Nitrate


  most widely precipitation titrations involve the use of
• Argentometric titrations 


  precipitation titrations are often referred to as
• Standard Solutions (VS)


  0.1 N Silver nitrate (AgNO3) and 0.1 N Ammonium thiocyanate (NH4SCN)
• AgNO3


  0.1 N Silver nitrate
• NH4SCN


  0.1 N Ammonium thiocyanate
• Give the 3 Determination of End Point 


  Cessation of precipitation or appearance of turbidity, Use of internal indicators, Instrumental methods (Potentiometric or Amperomeric)
• Ferric ammonium sulfate TS use in analysis of Silver and Mercuric ions by direct and residual titrations with Ammonium thiocyanate solution
• Potassium chromate TS


  it forms red precipitate of Silver chromate which seen against the background of white silver chloride
• Adsorption indicators


  used in analysis of halides by direct titration with AgNO3 solution. The endpoint of titration is indicated when the color of Silver halide precipitate changes abruptly
• Absorption Indicators

  Dichlorofluorescein (DCF)TS, Eosin Y TS, Tetrabromophemolphthalein ethyl ester (TEE) TS
• Gay-Lussac's Method

  Analyte: Halides (Ex. NaCl)

  AgCl: white precipitation

  AgI: yellow precipitation

  AgBr: pale yellow precipitation

  Titrant: AgNO3 VS

  Primary standard: NaCl

  Indicator: None

  Endpoint: Cessation Precipitation
• Liebig’s Method

  Analyte:           Cyanide, Organic nitrogenous compounds

  Titrant:             Sodium tetraphenyl boron VS

  Primary standard: KHP (MW: 204.22)

  Indicator:         Bromophenol Blue

  Endpoint:         Appearance of turbidity
• Mohr’s Method

  Type of titration: Direct titration

  Analyte:           Sodium lauryl sulfate (Sodium cation content)

  Titrant:             AgNO3 VS

  Primary standard: NaCl

  Indicator:         Potassium dichromate  

  Endpoint:         Red ppt (Ag2CrO4)
• Fajan’s Method

  Type of titration: Direct titration

  Analyte:           Phenylephrine, Tubocurarine, Meperidine

  Titrant:             AgNO3 VS

  Primary standard: NaCl

  Indicator:         Absorption indicators   

  Endpoint:         Pink surface of ppt. Ag halide
• Volhard’s Method

  Type of titration: Residual titration

  Analyte:           Aminophylline, Theophylline

  Titrant:             AgNO3 VS; NH4SCN VS

  Indicator:         Ferric ammonium Sulfate (Alum)   

  Endpoint:         Red brown precipitate of Ferric thiocyanate, Fe(SCN)3
• Assay of Sodium Chloride

  Official USP requirement: 99-100.5%

  Method:           Fajans or Volhard

  Indicator:         Ferric Alum Sulfate (Volhard)

                          Erosin Y (Fajans)