Types of complexometric titration

types of complexometric titration and titration curve

1. TYPES OF COMPLEXOMETRIC TITRATION Renjitha J R Assistant professor Mount Zion College of Pharmaceutical Sciences and Research, Adoor

2. 1) DIRECT TITRATION Direct titration is the simplest and most convenient method used in chelometry . In this method the solution containing the metal ion to be determined is buffered to the desire pH and directly titrated with standard solution of disodium edetate with suitable pm indicator until the indicator just changes colour . Metal ion + buffer + indicator titrate with EDTA Precipitation of hydroxide of the metal can prevent by addition of some auxiliary complexing agent such as tartarate or citrate or triethanolamine . Eg ; The metal ions which can determined by direct titration with EDTA are Ca2+ , Mg 2 +, Zn 2 + (Calcium Carbonate, Magnesium Hydroxide, Magnesium Sulphate , Zinc Stearate , Zinc Sulphate )

3. 2) BACKTITRATION OR RESIDUAL TITRATION This involves addition of an excess of standard EDTA solution to the metal being determined & excess is back titrated with standard solution of a second metal ion to a suitable end point at desired pH. Excess of standard EDTA solution is added to the analyte . The resulting solution is buffer to the desired ph and the excess of EDTA is back titrated with standard metal ion solution. A solution of ZnCl 2 / SO 4 /MgCl 2 /SO 4 / lead nitrate is often used for the purpose. The end point is detected with the aid of metal indicator .

4. 3) REPLACEMENT /SUBSTITUTION TITRATION When direct titration /back titration don’t give sharp end point , the metal may be determined by the displacement of an equivalent amount of Mg/ Zn from less stable EDTA complex . Ca , Pb & Hg can be determined using mordant black II as indicator by this method. This method involves quantitative displacement of 2 nd metal ion (M2) from a complex by the metal (M1) being determined. The free second metal is then titrated directly by standard EDTA solution. From this data we can calculate the concentration of M1 in the system.

5. 4) ALKALIMETRIC TITRATION OF METALS

6. 5) INDIRECT TITRATION This method is used for determination of ions such as anion and don’t react with chelating agents. The anion is first precipitated with a metal cation and the precipitate is washed and boiled with an excess of disodium EDTA solution to form the metal complex .

7. Eg 1;

8. Eg 2; Barbiturate will not react directly with EDTA and barbiturate forms complex with Hg 2+ ions. The titration of Hg- barbiturate with EDTA gives the concentration of equivalent amount of barbiturate. Barbiturate + EDTA no reaction Barbiturate -Hg (complex) + EDTA Hg –EDTA + Barbiturate

9. TITRATION CURVE IN COMPLEXOMETRIC TITRATION

10. pM [negative logarithm of the free metal ion concentration (-log Mn +)] is plotted against the volume of EDTA solution added , a point of inflexion occurs at the equivalence point. Buffer plays an important role in complexometric titrations , if solubility product of the metal hydroxide is low, it may be precipitated if the hydroxyl ion concentration is increased too much(alkaline pH) . Also at lower pH values(acidic pH) when the concentration of the metal ions is lower , the stability constant of the complexes will not be so high.

11. Titrant Large number of ionorganic and organic titrants have been used in complexometric titration. Eg ; poly amino carboxylic acid (amino acetic acid) Nitrilo triacetic acid EDTA DISODIUM EDETATE is much more water soluble , non hygroscopic and very stable.

12. Thank You