Home | | Modern Analytical Chemistry | Quantitative Applications - Titrations Based on Complexation Reactions

Chapter: Modern Analytical Chemistry: Titrimetric Methods of Analysis

Quantitative Applications - Titrations Based on Complexation Reactions

With a few exceptions, most quantitative applications of complexation titrimetry have been replaced by other analytical methods.

Quantitative Applications

With a few exceptions, most quantitative applications of complexation titrimetry have been replaced by other analytical methods. In this section we review the gen- eral application of complexation titrimetry with an emphasis on selected applica- tions from the analysis of water and wastewater. We begin, however, with a discus- sion of the selection and standardization of complexation titrants.

Selection and Standardization of Titrants 

EDTA is a versatile titrant that can be used for the analysis of virtually all metal ions. Although EDTA is the most com- monly employed titrant for complexation titrations involving metal ions, it cannot be used for the direct analysis of anions or neutral ligands. In the latter case, stan- dard solutions of Ag+ or Hg2+ are used as the titrant.

Solutions of EDTA are prepared from the soluble disodium salt, Na2H2Y• 2H2O. Concentrations can be determined directly from the known mass of EDTA; however, for more accurate work, standardization is accomplished by titrating against a solution made from the primary standard CaCO3. Solutions of Ag+ and Hg2+ are prepared from AgNO3 and Hg(NO3)2, both of which are sec- ondary standards. Standardization is accomplished by titrating against a solution prepared from primary standard grade NaCl.

Inorganic Analysis 

Complexation titrimetry continues to be listed as a standard method for the determination of hardness, Ca2+, CN, and Cl in water and waste- water analysis. The evaluation of hardness was described earlier in Method 9.2. The determination of Ca2+ is complicated by the presence of Mg2+, which also reacts with EDTA. To prevent an interference from Mg2+, the pH is adjusted to 12–13, precipitating any Mg2+ as Mg(OH)2. Titrating with EDTA using murexide or Eri- ochrome Blue Black R as a visual indicator gives the concentration of Ca2+.

Cyanide is determined at concentrations greater than 1 ppm by making the sample alkaline with NaOH and titrating with a standard solution of AgNO3, forming the soluble Ag(CN)2 complex. The end point is determined using p-dimethylamino benzalrhodamine as a visual indicator, with the solution turn- ing from yellow to a salmon color in the presence of excess Ag+.

Chloride is determined by titrating with Hg(NO3)2, forming soluble HgCl2. The sample is acidified to within the pH range of 2.3–3.8 where diphenylcarbazone, which forms a colored complex with excess Hg2+, serves as the visual indicator. Xy- lene cyanol FF is added as a pH indicator to ensure that the pH is within the desired range. The initial solution is a greenish blue, and the titration is carried out to a purple end point.

Quantitative Calculations 

The stoichiometry of complexation reactions is given by the conservation of electron pairs between the ligand, which is an electron-pair donor, and the metal, which is an electron-pair acceptor; thus


This is simplified for titrations involving EDTA where the stoichiometry is always 1:1 regardless of how many electron pairs are involved in the formation of the metal–ligand complex.


The principle of the conservation of electron pairs is easily extended to other com- plexation reactions, as shown in the following example.






Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail
Modern Analytical Chemistry: Titrimetric Methods of Analysis : Quantitative Applications - Titrations Based on Complexation Reactions |

Related Topics

Modern Analytical Chemistry: Titrimetric Methods of Analysis


Privacy Policy, Terms and Conditions, DMCA Policy and Compliant

Copyright © 2018-2023 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.