ANALYSISLAB

• Precipitimetry


  Precipitation Titrimetric Analysis, based on the formation of relatively insoluble substances (precipitates) to cause the reaction to go to completion quantitatively
• 
  

  Complexometry


  Titration analysis based on the formation of soluble complexes
• Silver nitrate


  Most widely used precipitating agent/standard solution
• Argentometry


  Determination of halides if the titrant used is AgNO3 standard solution
• Indicators used in precipitimetry

  • Ferric Ammonium Sulfate (ferric alum) - for direct and residual titration using NH4SCN as standard solution, endpoint is white (AgSCN) to reddish brown complex (FeSCN2+)
  • Adsorption indicators like Dichlorofluorescein (DCF), Eosin Y, Tetrabromophenolphthalein ethyl ester (TEE) - used in analysis of halides by direct titration with AgNO3, are weak acids, endpoint best seen in diffused-light condition
• 0.1N AgNO3


  Standard working solution
• NaCl


  Primary standard
• Standardization of 0.1N AgNO3

  Direct precipitimetry, stock solution 0.1N AgNO3, titrant 0.1N AgNO3, primary standard NaCl, indicator Eosin Y, endpoint magenta (purplish red)
• Working equations for standardization of 0.1N AgNO3
• 0.1N NH4SCN


  Secondary standard
• Standardization of 0.1N NH4SCN


  Direct precipitimetry, stock solution 0.1N NH4SCN, titrant 0.1N NH4SCN, secondary standard 0.1N AgNO3 (from M4 L1), indicator ferric alum, endpoint reddish-brown
• Working equations for standardization of 0.1N NH4SCN
• Volhard method


  A form of residual or back-titration, complete precipitation of insoluble silver salts with the addition of excess silver nitrate followed by titration of the unreacted silver nitrate with ammonium thiocyanate, ferric alum as indicator (reddish-brown endpoint)
• Iodized salt sample


  • Dried, sieved, edible and iodized for human consumption, NaCl content NLT 97% (w/w), body requirement of potassium iodate (50-84 mg/kg) and iodine (30-50 mg/kg)
• Assay of sodium chloride content in iodized salt by Volhard method


  Residual precipitimetry, titrant 0.1N NH4SCN, standard solutions 0.1N NH4SCN (M4 L2) and 0.1N AgNO3 (M4 L1), analyte sodium chloride (NaCl), indicator ferric alum, endpoint reddish-brown, specification NLT 97%
• Working equations for assay of NaCl content in iodized salt
• NaCl


  Content in Iodized salt
• Precipitimetry


  Working Equations
• Complexometry


  Working Equations
• Lesson: Preparation and Standardization of 0.05 M EDTA Solution
• LIGAND


  A molecule which provides groups for attachment to metal ions
• METAL COMPLEX


  a.k.a. Coordination compounds
• CHELATE


  A complex that contains two or more groups that can donate electrons
• Complexation Reaction


  1. LIGAND

  2. METAL

  3. COMPLEX
• Compleximetry (Complexation Titrimetric Analysis)


  Metal ion reacts with a suitable ligand to form a complex, and the end point is determined by an indicator or an appropriate instrumental method
• Metal (Analyte)


  Ligand (Titrant)
• EDTA (Ethylenediaminetetraacetic acid)


  • C10H14N2Na2O8 · 2H2O (MW=372)
  • A hexadentate ligand
  • Commonly used in the concentration of 0.05 M
• Standardization of 0.05 M EDTA

  1. 0.05 M EDTA (Metal)

  2. CaCO3 (ligand)

  3. UNKNOWN (Not Standardized yet)

  4. KNOWN (Pure compound, known weight)

  5. The STANDARD WORKING SOLUTION

  6. The Primary Standard

  7. Indicator: Hydroxynaphthol Blue (HNB)

  8. Preferred End point: Blue
• Standardization of 0.05 M EDTA

  • Type and Methods: Direct Compleximetry
  • Titrant: 0.05 M EDTA
  • Stock Solution: 0.05 M EDTA
  • Primary Standard: Calcium carbonate (CaCO3)
  • Indicator: Hydroxynaphthol Blue
  • Endpoint: Blue color
• • Notes: Addition of HCl to solubilize and stabilize CaCO3
  • Addition of NaOH Alkalizes the solution to pH 12.3-12.5
  • Stabilizes the Ca-EDTA complex
  • Masks Mg ions
• Lesson: Assay of Calcium sulfate by EDTA titration
• Calcium sulfate (CaSO4)


  • An odorless, white powder
  • Exist as: Anhydrous, Dihydrate (Gypsum), Hemihydrate (Plaster of Paris)
  • Uses: Dessicant, Building or molding material
• Calcium carbonate (CaCO3)


  PRIMARY STANDARD
• Assay of Calcium sulfate

  • Type and Methods: Direct Compleximetry
  • Titrant: 0.05 M EDTA
  • Standard Solution: 0.05 M EDTA (M4 L4)
  • Analyte: Calcium sulfate (CaSO4)
  • Indicator: Hydroxynaphthol Blue
  • Endpoint: Blue color
  • USP limit: 98 - 101%
• Other Application of EDTA Titration: Determination of Water Hardness