Complexometric Titration

1. COMPLEXOMETRIC
TITRATIONS
LIDIA MARIA DSOUZA
198216

2. WHAT IS TITRATION
• TITRATION IS A PROCESS IN WHICH A STANDARD REAGENT IS ADDED TO A
SOLUTION OF AN ANALYTE UNTIL THE REACTION BETWEEN THE ANALYTE AND
REAGENT IS JUDGED TO BE COMPLETE

3. 1. ACID-BASE TITRATION:IT IS A QUANTITATIVE ANALYSIS METHOD TO
DETERMINE AN ACID’S OR BASES’ CONCENTRATION BY PRECISELY
NEUTRALIZING THEM WITH A STANDARD SOLUTION OF EITHER ACID
OR BASE OF KNOWN CONCENTRATION.
2. REDOX TITRATIONS:THE REDOX TITRATION IS ALSO KNOWN AS
AN OXIDATION AND REDUCTION.IN THIS TYPE OF TITRATION, THE CHEMICAL
REACTION TAKES PLACE WITH A TRANSFER OF ELECTRONS IN THE
REACTING IONS OF AQUEOUS SOLUTIONS.
3. PRECIPITATION TITRATIONS:THE TITRATION IS BASED ON THE INSOLUBLE
PRECIPITATE FORMATION WHEN THE TWO REACTING SUBSTANCES ARE
BROUGHT INTO CONTACT ARE CALLED PRECIPITATION TITRATION.
4. COMPLEXOMETRIC TITRATIONS:THE COMPLEXOMETRIC TITRATION IS
WHERE AN UNDISSOCIATED COMPLEX IS FORMED AT AN EQUIVALENCE
POINT.

4. WHAT ARE
COMPLEXOMERTIC
TITRATIONS?
• IT IS A FORM OF A VOLUMETRIC ANALYSIS IN WHICH THE FORMATION OF THE
COLORED COMPLEX IS USED TO DETERMINE THE END POINT OF THE
TITRATION
• MANY COMPLEX FORMING IONS HAVE A TENDENCY TO FORM A STEPWISE
COMPLEX AND WITH THE AID OF SUITABLE INDICATOR THESE COMPLEX IONS
CAN BE TITRATED
• COMPLEXOMETRIC TITRATIONS ARE PARTICULARLY USEFUL FOR THE
DETERMINATION OF THE MIXTURES OF DIFFERENT METAL ION PRESENT IN
THE SOLUTION
• AN INDICATOR CAPABLE OF PRODUCING COLOR CHANGE IS USUALLY USED

5. THE FORMATION OF COMPLEXES
• MOST METAL IONS REACT WITH ELECTRON PAIR DONORS TO FORM COORDINATION
COMPLEXES
• M+L->ML COMPLEX
• THE DONOR SPECIES ALSO CALLED AS LIGANDS ,MUST HAVE ATLEAST ONE PAIR OF
UNSHARED ELECTRONS AVAILABLE FOR BOND FORMATION
• COMPLEXOMETRIC TITRATIONS ARE BASED ON A PARTICULAR CLASS OF
COORDINATION COMPOUNDS CALLED CHELATES.
• A CHELATE IS PRODUCED WHEN A METAL ION COORDINATES WITH TWO OR MORE
DONOR GROUPES OF A SINGLE LIGAND TO FORM A FIVE-OR SIX –HETERCYCLIC RING

6. • A LIGAND THAT HAS A SINGLE DONOR GROUP,SUCH AS AMMONIA IS CALLED
UNIDENTATE.
• A LIGAND THAT HAS TWO DONOR GROUPS AVAILABLE FOR COVALNE BONDING ARE
CALLED BIDENTATE LIGAND. EX:GLYCINE
• LIGANDS WITH MORE THAN 2 DONOR GROPS ARE CALLED POLYDENTATE.EX:EDTA,18-
CROWN-6
• ANOTHER IMPORTANT TYPE OF COMPLEX IS FORMED BETWEEN METAL IONS AND CYCLIC
ORGANIC COMPOUNDS KNOWN AS MACROCYCLES.THESE MOLECULES CONTAIN NINE OR
MORE ATOMS IN A CYCLE INCLUDE ATLEAST THREE HETEROATOMS,USUALLY
OXYGEN,NITROGEN OR SULFER.EX CROWN ETHERS

7. • THE COMPLEX FORMED SHOULD BE SOLUBLE UNDISSOLVED AND
STOICHIOMETRIC FOR WHICH FALLOWING CONDITIONS ARE APPLIED
1. A SUITABLE LIGAND
2. EXPERIMENTAL CONDITIONS (SUCH AS PH,TEMPERATURE,USE OF BUFFER ETC)ARE
MAINTAINED SUTAIBLE FOR A OPTIMUM TITRATION
3. SELECTING A SUTAIBLE METHOD FOR THE DETECTION OF END POINT OF THETITRATIO
THE MOST WIDELY USED CHELATING AGENT FOR COMPLEXOMETRIC TITRATION WHICH
SATISFIES THE ABOVE CONDITION IS ETHYLENE DIMINE TETRA ACIDIC ACID(EDTA)WHICH
FORMS 1:1 STRONG COMPLEX WITH METAL ION OF ANY CHARGE

8. THE ENDPOINT DETECTION IN COMPLEXOMETRIC
TITRATION CAN BE DONE BY TWO METHODS.
1. VISUAL METHOD
2. INSTRUMENTAL METHOD

9. VISUAL METHOD
ONE OF THE MOST COMMON METHODS FOR DETERMINATION OF
ENDPOINT OWING TO ITS SIMPLICITY, LEAST COST AND ACCURACY.
FOLLOWING ARE SOME OF THE VISUAL METHODS USED FOR
DETERMINING THE END POINT OF THE COMPLEXOMETRIC
TITRATIONS.
• METALLOCHROMIC OR PM INDICATORS
• PH INDICATORS
• REDOX INDICATORS

10. INSTRUMENTAL METHOD
USE OF VISUAL METHODS IN DETERMINING THE ENDPOINT IS NOT FREE FROM
LIMITATIONS INCLUDING INACCURACY OR HUMAN VISUAL ERRORS. SOME
INSTRUMENTAL TECHNIQUES USED IN ENDPOINT DETERMINATION ARE
• PHOTOMETRY
• POTENTIOMETRY
• MISCELLANEOUS METHODS.

11. TYPES OF COMPLEXOMERTIC TITRATION
THERE ARE TYPES :
1. DIRECT TITRATION
2. INDIRECT TITRATION
3. BACK TITRATION
4. DISPLACEMENT TITRATION

12. DIRECT TITRATION
• IN THIS CASE, THE METAL ION IS TITRATED WITH A STANDARD SOLUTION OF
EDTA. THE SOLUTION CONTAINING THE METAL ION IS BUFFERED TO AN
APPROPRIATE PH AT WHICH THE STABILITY CONSTANT OF THE METAL-EDTAS
LARGE. THE FREE INDICATOR HAS A DIFFERENT COLOUR FROM THAT OF THE
METAL-INDICATOR COMPLEX.

13. INDIRECT TITRATION
• CERTAIN ANIONS THAT FORM PRECIPITATE WITH METAL CATIONS AND DO NOT
REACT WITH EDTA CAN BE ANALYZED INDIRECTLY. 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.
• THE PROTONS FROM DISODIUM EDTA ARE DISPLACED BY A HEAVY METAL AND
TITRATED WITH SODIUM ALKALI. THEREFORE, THIS METHOD IS ALSO CALLED
ALKALIMETRIC TITRATION.
• FOR EXAMPLE, BARBITURATES CAN BE DETERMINED BY THIS METHOD.

14. BACK TITRATION
IN CERTAIN CIRCUMSTANCES A PARTICULAR METAL ION CANNOT BE TITRATED
DIRECTLY. THIS INCLUDES SITUATIONS WHERE THE METAL ION PRECIPITATES IN THE
ABSENCE OF EDTA.THE METAL ION REACTS TOO SLOWLY WITH EDTA.THE METAL ION
FORMS AN INERT COMPLEX.NO SUITABLE INDICATOR IS AVAILABLE.IN THESE CASES A
BACK TITRATION IS REQUIRED. THIS INVOLVES ADDITION OF A KNOWN EXCESS OF
EDTA TO THE METAL ION (BUFFERED TO AN APPROPRIATE PH). THEN, THE EXCESS EDT
A IS TITRATED WITH A STANDARD SOLUTION OF A DIFFERENT METAL ION. THE
CHOICE OF A SECOND METAL ION IS IMPORTANT AS IT MUST NOT DISPLACE THE
ANALYTE METAL ION FROM ITS EDTA COMPLEX.
THIS METHOD IS USEFUL FOR CATIONS SUCH AS CHROMIUM AND COBALT THAT
REACT SLOWLY WITH EDTA

15. DISPLACEMENT TITRATION
• IN DISPLACEMENT TITRATION,AN UNMEASURED EXCESS OF A SOLUTION
CONTAING THE MAGNESIUM OR ZINC COMPLEX OF EDTA IS INTRODUCED INTO
THE ANALYTE SOLUTION.I
• IF THE ANALYTE FORMS A MORE STABLE COMPLEX THAN THAT OF MAGNESIUM
OR ZINC,THE FALLOWING DISPLACEMENT REACTION OCCURES
• WHERE M2+ REPRESENTS THE ANALYTE CATION.THE LIBERATED MAGNESIUM OR
IN SOME CASES ZINC ION ,IS THEN TITRATED WITH A STANDARD EDTA
SOLUTION

16. • THE PROGRESS OF A COMPLEXOMERTIC
TITRATION IS GENERALLY ILLUSTRATED BY A
TITRATION CURVE WHICH IS USUALLY A PLOT
OF PM=-LOG [M] AS A FUNCTION OF THE
VOLUME OF TITRANT ADDED
• MOST OFTEN ,IN COMPLEXOMERTIC
TITRATIONS THE LIGAND IS THE TITRANT AND
THE METAL ION IS THE ANALYTE
• MANY PRECIPITATION TITRATIONS USE METAL
ION AS THE TITRANT.

17. INDICATOR
S
• INDICATORS USED IN COMPLEXOMETRIC TITRATION ARE TO SOME EXTENT SIMILAR TO THOSE USED IN ACID-BASE TITRATIONS. THEIR COLOR CHANGES DEPENDING ON
THE CONCENTRATION OF METAL IONS, JUST LIKE COLOR OF PH INDICATORS CHANGES DEPENDING ON THE H+ CONCENTRATION.
• MECHANISM OF THIS COLOR CHANGE IS DIFFERENT, AS ALL COMPLEXOMETRIC INDICATORS ARE JUST COMPLEXING AGENTS, CHANGING THEIR COLOR DEPENDING ON
WHETHER THEY ARE FREE IN THE SOLUTION, OR LIGANDS IN THE COMPLEX. IN MOST CASES THEY ARE ALSO WEAK ACIDS OR BASES, AND QUITE OFTEN THEIR COLOR
DEPENDS ON THE SOLUTION PH.
• COLOR CHANGE SHOWS THAT THE INDICATOR HAS BEEN DISPLACED FROM THE METAL CATIONS IN SOLUTION WHEN THE END POINT HAS BEEN REACHED. THUS IT
SERVES AS THE ENDPOINT INDICATOR. SOME OF THE METAL ION INDICATORS ARE;
• 1. MUREXIDE
• 2. ERIOCHROME BLACK T (SOLOCHROME BLACK)
• 3. PATTON AND REEDER
• 4. SOLOCHROME DARK BLUE (CALCON)
• 5. CALMAGITE
• 6. CALCICHROME
• 7. FAST SULPHON BLACK F
• 8. BROMO PYROGALLOL RED
• 9. XYLENOL ORANGE
• 10. THYMOLPHTHALEIN COMPLEXONE (THYMOLPHTHALEXONE)
• 11. METHYLTHYMOL BLUE (METHYLTHYMOL BLUE COMPLEXONE)
• 12. ZINCON.
• 13. VARIAMINE BLUE.

19. MASKING AND DAMASKING AGENTS

21. SELECTIVITY

22. COMPLEXOMETRIC TITRATIONS WITH
EDTA
• EDTA FORMS STABLE COMPLEXES WITH MOST METAL IONS – THE EXCEPTIONS
BEING THE GROUP 1 CATIONS. THE STABILITY OF THE COMPLEXES CAN BE
ATTRIBUTED TO THE CHELATE EFFECT; WHEN COMPLEXING A METAL ION EDTA
SURROUNDS THE METAL CATION, FORMING A NUMBER OF FIVE-MEMBERED
RINGS.

23. APPLICATIONS
COMPLEXOMETRIC TITRATIONS ARE USEFUL IN DIFFERENT FIELDS NAMELY
ANALYTICAL CHEMISTRY AND PHARMACEUTICAL SCIENCES
• IN ANALYTICAL FIELD THERE ARE DIRECT TITRATION ,INDIRECT
TITRATION,BACK TITRATION AND DISPLACEMENT TITRATION METHODS
DEPENDING ON WHAT IS BEING TITRATED AND THE GOAL IS TO FIND THE
CONCENTRATION.
• IN PHARMACEUTICAL SCIENCES THE COMPLEXOMETRIC TITRATIONS ARE USED
TO FIND THE AMOUNT OF METALS IN DIFFERENT FORMULATION AND ALSO TO
DETERMINE THE HARDNESS OF WATER.

24. ADVANTAGES OF COMPLEXOMETRIC
TITRATION

25. THANK YOU