complexometric titration

1. COMPLEXOMETRIC
TITRATIONS
SHILPA JOY
ASSISTANT PROFESSOR
DEPARTMENT OF CHEMISTRY
KURIAKOSE ELIAS COLLEGE
MANNANAM

2. Complexometric titrations or
Chelatometry
Volumetric analysis in which the formation
of colored complex is used to indicate the end
point of a titration.
Estimation of metal ion in solution
Stability of the complex formed is the
determining factor
Indicator- unambiguous color change.

3. 1. Reaction reaches equilibrium rapidly after each
portion of titrant is added
2. Interfering situations do not arise
3. Complexometric indicator capable of locating
equivalence point with fair accuracy is available
4. the technique involves titrating metal ions with a
complexing agent or chelating agent(ligand)
Metal ion + complexing agent complex ion

4. EDTA – Ethylene diamine tetraacetic acid- titrant
Erio-chrome black-T --- indicator

5. o 4- hydroxyl groups and two amine groups- act as
electron pair donor
oThe ability of EDTA to donate 6 lone pairs of electrons for
the formation of coordinate covalent bonds to metal
cations makes EDTA a hexadentate ligand.
o EDTA is usually only partially ionized form, thus forms
fewer than 6 coordinate covalent bonds with the metal.

6. Disodium EDTA is commonly used to standardise
aqueous solutions of metal cations.
Na2H2Y forms 4 coordinate covalent bond at a Ph <12 .
EDTA forms an octahedral complex with most M+2 ions
in aqueous solution

7. • EDTA is extensively used in the standardisation of
metal cation solutions since the formation constant for
the most metal cation –EDTA complexes are very high.
M2+ + H4
Y MH2
Y + 2H+
equilibrium lies far to the right.
carrying out the reaction in basic buffer solution
removes H+ as it is formed , which also favours the
formation of the complex product.
Formation of metal cation –EDTA complex goes on
completion- advantage

8. Magnesium
Calcium
Cadmium
Lead
Copper
Nickel
cobalt
Iron
Bismuth
Thorium
Zironium
Direct
determination
Analyte is titrated with standard EDTA solution buffered at a pH
where kf is large.

9. Back titration
4 dozen of elements- direct titration with EDTA
with a suitable metal ion indicator
non availability of suitable indicator– direct
titration is not possible
In back titration , excess standard solution of
EDTA is added to the analyte and excess EDTA
or unreacted EDTA is back titrated against a
standard solution of Mg+2 or Zn+2 using
eriochrome black T

10. MASKING OF IONS
Mg+2 or Ca+2 ions can be titrated in the
presence of interfering Cd+2,Cu+2,or Ni+2 by
adding cyanide ion reaction mixture
Cyanide act as masking agent
It can form complexes with Cd+2,Cu+2,or Ni+2
thereby eliminating interference

11. Advantages
Estimates hardness of water –calcium and
magnesium ions.
EDTA is a convenient reagent, it always react
with metals 1:1 basis, making calculation easy.
Selection of solution Ph allows to determine
one metal in the presence of other
Cations with high charges (Fe+3, Bi+3) have large
stability constant,so they can be titrated at low
pH , in the presence of divalent cations which will
not interfere in this condition.

12. Indicators
Eriochrome Black T
Eriochrome Red B
Murexide
Fast Sulphon Black
.

13. Triethanolamine – comlpexant to
mask
Aluminium ions- before performing
titration
Multiple metal ins can be subsequently
titrated by careful control of the pH

14. These dyes binds metal cations in the solution to form
colored complexes.
Since EDTA binds to the metal cations more strongly
than does the dye used as an indicator, the EDTA will
displace the dye from the metal cations as it is added
to the solution of analyte
MgEbT(red) + EDTA(colourless)
Mg Edta (colourless)+ EbT(blue)

15. Titration curve