complexation reaction

• Complexometric method


  A form of volumetric analysis in which the formation of a colored complex is used to indicate the end point of a titration
• Chelate


  • The complex formed, derived from the Greek term meaning "clawlike", literally wrap themselves around a metal ion
  • If the combining molecule contains 2 or more groups that donate electrons
• Complex


  A molecule or ion formed by the reaction of 2 or more ions or molecules capable of independent existence; metal ion combines with a molecule which can donate electrons
• EDTA


  Ethylenediaminetetraacetic acid, the most important chelating agent
• Types of complexometric titrations

  • Direct titration
  • Residual titration
  • Replacement/Displacement titration
• Masking


  Determination of a metal in the presence of another metal by adding a masking agent that will bind tightly to a metal ion so it will not titrate with EDTA
• Indicators for complexometric titrations


  • Diphenylamine TS
  • Dithizone TS
  • Eriochrome Black TS
  • Hydroxynaphthol blue
  • Murexide (Acid Ammonium Purpurate)
  • Naphthol green TS
• Ferric chloride titration


  Used for the determination of sodium fluoride, based on the reaction of sodium fluoride with ferric chloride to form a stable complex
• Types of water hardness

  • Temporary hardness (due to bicarbonate ion, HCO3-)
  • Permanent hardness (due to presence of ions Ca, Mg, Fe and SO4)
• The most important complexation reaction is between a metal ion and a complexing agent
• EDTA reacts with metal ions to form a water soluble, stable complex or chelate compound
• The reaction between EDTA and metal ions is rapid and quantitative with such polyvalent metal ions as Al, Bi, Ca, Cu, Hg, Mg and Zn
• The 4 oxygen and 2 nitrogen atoms of EDTA are capable of entering a complexation reaction with a metal ion, making it a hexadentate molecule
• The EDTA molecule which provides groups for attachment to metal ions is called a Ligand
• The disodium salt of EDTA is preferred over the free acid in preparing the standard solution as it is much more soluble, non-hygroscopic and very stable
• Indicators for complexometric titrations must form colored complex ions with the metal ion in high dilution, give up the metal ion to the titrant EDTA for complexing, and not compete with it
• Calcium, magnesium and zinc are determined by direct titration with EDTA using indicators like hydroxynaphthol blue, eriochrome black, and xylenol orange
• Aluminum, bismuth and manganese compounds are determined by residual titration methods to avoid errors due to precipitation of the metal as hydroxides in alkaline media
• Displacement/replacement titrations are used when direct or back titration do not give sharp end points, where the analyte ion displaces a second metal from an EDTA complex which is then titrated with EDTA
• Masking agents are compounds capable of entering a complexation reaction that can be used to prevent other ions from interfering in a given titration
• Water hardness is determined either by atomic absorption spectrophotometry or by complexometric titration
• Temporary hardness is due to bicarbonate ions (HCO3-) and can be removed by boiling, while permanent hardness is due to the presence of ions like Ca, Mg, Fe and SO4 and cannot be eliminated by boiling
• Complexometric titration(sometimes chelatometry) is a form of volumetric analysis in which the formation of a colored complex is used to indicate the endpoint of a titration.
• Complexometric Titration is useful in the determination of a mixture of different metal ions in solution.
• Inorganic products containing metal ions (Al, Bi, Ca, Mg, Zn) are analyzed using gravimetric methods(time consuming-precipitation, filtration, washing, drying).
• The analytical reagent disodium ethylenediamine tetraacetate (EDTA), a new volumetric procedure evolved for metal determination