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+ , Mg2+, Zn2+ (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 ZnCl2/ SO4/MgCl2/SO4/ 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 2nd
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.

6. 4) ALKALIMETRIC TITRATION OF METALS

7. 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.

8. Eg 1;

9. 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

10. TITRATION CURVE IN COMPLEXOMETRIC
TITRATION

11. 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.

13. 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.

14. Thank You