M4 Precipitimetry and Complexometry

• Most widely used precipitating agent/standard solution in determination of halides


  Silver Nitrate
• If the titrant used is AgNO3 standard solution

  Argentometry
• Based on the formation of relatively insoluble substances to cause the reaction to go to completion quantitatively


  Precipitimetry
• Indicators Used in preparation and standardization of 0.1N Silver Nitrate

  •Ferric Ammonium Sulfate (ferric alum)

  –Direct and residual titration

  –Use NH4SCN as standard solution

    –Endpoint: White(AgSCN) > Reddish brown complex (FeSCN2)
• Absorption Indicators

  1. Dichlorofluorescein (DCF)
  2. Eosin Y
  3. Tetrabromophenolphthalein ethyl ester (TEE)
• •Used in analysis of halides by direct titration w/ AgNO3 as standard solution


  Adsorption Indicators
• Adsorption Indicators

  • Used in analysis of halides by direct titration w/ AgNO3 as standard solution
  • Are weak acids
  • Endpoint best seen in diffused-light condition
• preferred end point of standardization of 0.1N AgNO3


  pinkish to magenta
• Standardization of 0.1N AgNO3

  A) 0.1N AgNO3

  B) NaCl

  C) pinkish to magenta

  D) EOSIN Y

  
• Standardization of 0.1N AgNO3

  Type and Method: Direct Precipitimetry

  Stock solution: 0.1 N AgNO3

  Titrant: 0.1 N AgNO3

  Primary Standard: Sodium chloride (NaCl)

  Indicator: Eosin Y

  Endpoint: Magenta (Purplish red)
• Standardization of 0.1N NH4SCN

  A) 0.1N NH4SCN

  B) 0.1N AgNO3

  C) FERRIC ALUM

  D) Reddish Brown

  
• Standardization of 0.1 N NH4SCN

  Type and Method: Direct Precipitimetry

  Stock solution: 0.1 N NH4SCN

  Titrant: 0.1 N NH4SCN

  Secondary Std: 0.1 N AgNO3 (M4 L1)

  Indicator: Ferric alum

  Endpoint: Reddish-brown
• A form of residual or back-titration

  Volhard Method
• Volhard Method

  • A form of residual or back-titration
  • Complete precipitation of insoluble silver salts with the addition of excess silver nitrate to precipitate
  • Followed by titration of the unreacted silver nitrate with ammonium thiocyanate
  • Ferric alum as indicator (reddish-brown endpoint)
• IODIZED SALT

  • Dried, sieved, edible and iodized for human consumption
  • NaCl content: NLT 97% (w/w)
  • Body requirement:

  Potassium iodate (50-84 mg/kg)

  Iodine (30-50 mg/kg)
• Assay of Sodium Chloride

  A) FERRIC ALUM

  B) NH4SCN

  C) Reddish Brown

  D) AgNO3

  E) NaCl

  F) Analyte

  G) AgNO3

  
• Assay of NaCl Content in Iodized salt

  Type and Method: Residual Precipitimetry (Volhard method)

  Titrant: 0.1 N NH4SCN

  Standard Solns: 0.1 N NH4SCN , 0.1 N AgNO3

  Analyte: Sodium chloride (NaCl)

  Indicator: Ferric alum

  Endpoint: Reddish-brown

  Specification: NLT 97 %
• A molecule which provides groups for attachment to metal ions

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

  Chelate
• Complexation Reaction

  A) Coordination Compounds

  B) CHELATE

  C) LIGAND

  
• Complexation Reaction:

  Metal + Ligand = COMPLEX
• 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 as titranD + Ligand as titranT


  Compleximetry (Complexation Titrimetric Analysis)
• EDTA

  A) Ethylenediaminetetraaetic acid

  B) hexadentate

  C) 0.05

  
• Standardization of 0.05M EDTA

  A) CaCO3

  B) 0.05M EDTA

  C) Hydroxynaphtol Blue

  D) BLUE

  
• Standardization of 0.05 M EDTA

  Type and Method: Direct Compleximetry

  Titrant: 0.05M EDTA

  Stock Solution: 0.05M EDTA

  Primary Standard: Calcium carbonate (CaCO3)

  Indicator: Hydroxynaphthol Blue

  Endpoint: Blue Color
• Notes(EDTA):

  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
• Assay of Calcium sulfate by EDTA titration

  SAMPLE USED:Calcium sulfate (CaSO4)

  • An odorless, white powder

  Exist as:

  • Anhydrous
  • Dihydrate (Gypsum)
  • Hemihydrate (Plaster of Paris)

  Uses:

  • Dessicant
  • Building or molding material
• Assay of Calcium sulfate

  Type and Methods: Direct Compleximetry

  Titrant: 0.05M EDTA

  Standard Solution: 0.05 EDTA

  Analyte: Calcium Sulfate (CaSO4)

  Indicator: Hydrocynaphthol Blue

  Endpoint: Blue Color

  USP limit: 98-101%
• The capacity of cations in water to form sparingly soluble products that cause "scum" in the sink or bathtub

  Water hardness
• Water Hardness

  • The capacity of cations in water to form sparingly soluble products that cause “scum” in the sink or bathtub
  • Expressed in terms of CaCO3 or Ca content

  Types:

  1. TEMPORARY water hardness

  • Due to presence of bicarbonates

  2. PERMANENT water hardness

  • Due to presence of chlorides and sulfates