TITRIMETRIC ANALYSIS

• Titrimetric 


  A group of analytical methods based on determining the quantity of a reagent of known concentration that is required to react completely with the analyte
• Titration


  A process in which a standard reagent is added to a solution of an analyte until the reaction between the analyte and reagent is judged to be complete
• Types of titrimetry

  • Volumetric titrimetry
  • Coulometric titrimetry
• Types of reactions in titrimetry

  • Complex formation reactions
  • Precipitation reactions
• Standard solution/titrant


  A reagent of known concentration that is used in a titrimetric analysis
• Back-titration


  A process in which the excess of a standard solution used to consume an analyte is determined by titration with a second standard solution
• Equivalence point


  The point in a titration when the amount of added standard reagent is equivalent to the amount of analyte
• End point


  The point in a titration when a physical change occurs that is associated with the condition of chemical equivalence
• Titration error


  The difference in volume or mass between the equivalence point and the end point
• Indicator

  A substance added to the analyte solution to give an observable physical change (the end point) at or near the equivalence point
• Primary standard


  A highly purified compound that serves as a reference material in all volumetric and mass titrimetric methods
• Secondary standard


  A compound whose purity has been established by chemical analysis and that serves as the reference material for a titrimetric method of analysis
• Important requirements for a primary standard

  • High purity
  • Atmospheric stability
  • Absence of hydrate water
  • Ready availability at modest cost
  • Reasonable solubility in the titration medium
  • Reasonably large molar mass
• Desirable properties of standard solutions

  • Sufficiently stable
  • React rapidly with the analyte
  • React completely with the analyte
  • Undergo a selective reaction with the analyte
• Methods for establishing the concentration of standard solutions

  • Direct method
  • Standardization
• Types of titration curves

  • Sigmoidal curve
  • Linear segment curve
• Neutralization titrations

  Titrations used to determine the concentration of analytes that are themselves acids or bases or that are convertible to such species by suitable treatment
• Neutralization titrations involve the combination of hydronium (H3O+) and hydroxyl ions (OH-) to form water
• Reagents for neutralization titrations

  • Strong acids
  • Strong bases
• Tris-(hydroxymethyl) aminomethane (TRIS or THAM)


  A primary standard for acids
• Potassium hydrogen phthalate


  A primary standard for bases
• Acid/base indicator


  A weak organic acid or a weak organic base whose undissociated form differs in color from its conjugate form
• Buffer


  A mixture of a weak acid and its conjugate base or a weak base and its conjugate acid that resists changes in pH of a solution
• Buffer capacity


  The number of moles of strong acid or strong base that causes one liter of the buffer to change pH by one unit
• End points in neutralization titrations

  • Visual end point based on indicators
  • Potentiometric end point
• Kjeldahl method


  Most common method for determining organic nitrogen that is based on neutralization titration
• Dumas method


  The sample is mixed with powdered copper(II) oxide and ignited in a combustion tube to give carbon dioxide, water, nitrogen, and small amounts of nitrogen oxides
• Chemiluminescence method


  The sample is combusted at 1100°C to convert the nitrogen to nitric oxide, which is then oxidized to nitrogen dioxide, giving off visible radiation
• Determining sulfur


  The sample is burned in a stream of oxygen, and the sulfur dioxide formed is collected and titrated with standard base
• Determining ammonium salts


  The ammonium salts are converted to ammonia, which is collected and titrated
• Determining nitrate or nitrite


  The method for ammonium salts can be extended to the determination of inorganic nitrate or nitrite
• Determining carbonate and carbonate mixtures


  Requires two titrations, one with an alkaline-range indicator and the other with an acid-range indicator
• Complex formation reagents

  • Ions, other than hydronium and hydroxyl ions, that form complexes
• Elemental Analysis - Nitrogen


  1. Combust sample at 1100°C to convert nitrogen to nitric oxide

  2. Introduce ozone to oxidize nitric oxide to nitrogen dioxide

  3. Measure intensity of visible radiation (chemiluminescence)
• Elemental Analysis - Sulfur


  1. Burn sample in oxygen stream

  2. Collect sulfur dioxide in dilute hydrogen peroxide

  3. Titrate sulfuric acid with standard base
• Determining Inorganic Substances - Ammonium salts


  1. Convert to ammonia

  2. Collect and titrate ammonia
• Determining Inorganic Substances - Nitrate or nitrite


  Use same method as for ammonium salts
• Determining Inorganic Substances - Carbonate and Carbonate Mixtures


  Require two titrations, one with alkaline-range indicator, one with acid-range indicator
• Complex Formation Reagents

  • Used for titrating cations
  • Many complexes are colored or absorb UV
  • Ligand is often the titrant, metal ion is the analyte
• Ligand

  Ion or molecule that forms covalent bond with cation or neutral metal atom by donating electron pair