1. Name: Dr. Pramod B. Thakur Class: T. Y. B
Name: Dr. Pramod B. Thakur Class: T.Y.B.Sc Subject: Analytical Chemistry Title of Topic: Complexometric
Titrations

2. COMPLEXOMETRIC TITRATIONS
TYBSc
Paper IV- USCH604
Analytical Chemistry
COMPLEXOMETRIC TITRATIONS
By Mr. P. B. Thakur

3. COMPLEXOMETRIC TITRATIONS
General introduction
EDTA titrations
Advantages and limitations of EDTA as the titrant
Absolute and conditional formation constants of
Metal-EDTA complex
Construction of Titration curve
Types of EDTA Titrations
Methods of increasing the selectivity of EDTA as a titrant
Metallachromic indicators
Theory Metallachromic indicators
Applications of Metallachromic indicators

4. What is complex???? How Complex forms????
Complex consists of an metal ion surrounded by molecules or anions.
How Complex forms????
Complex is formed by the combination of metal ion with electron donating group or nucleophile.

6. Complexometric Titrations:
A complexometric titration is technique of volumetric analysis in which a soluble, undissociated, stiochimetric complex is formed during the addition of titrant to the sample solution.
In Complexometric titration the formation of a colored complex is used to indicate the end point of a titration.
Complexometric titrations are particularly useful for the determination of a mixture of different metal ions in solution.
An indicator capable of producing an definite color change is usually used to detect the end-point of the titration.

7. Which complexation reaction can be used as a volumetric technique????
The reaction which reaches equilibrium rapidly after each portion of titrant is added.
The reactions in which interfering situations do not arise. e.g. The formation of several different complexes of the metal ion with the titrant, during the titration process.
The reaction in which a indicator is capable of locating equivalence point with fair accuracy is available.
Complexation titrations are particularly useful for the determination of a large number of metal ions in solution. In practice, the use of EDTA as a titrant is well established in such complexometric reactions.

8. EDTA Titrations: What is EDTA???
EDTA is Ethylene Diamine Tetra Acetic acid.
It has four carboxyl groups and two amine groups.

9. Commonly EDTA is represented in the acid form as H4Y.
EDTA = H4Y
Due to low solubility of acid form of EDTA in water,
its disodium dihydrate EDTA salt i.e. Na2H2Y.2H2O is used
disodium dihydrate EDTA
= Na2H2Y.2H2O

10. Different Forms of EDTA
EDTA = H4Y

11. EDTA has four carboxyl groups and two amine groups.
EDTA is polydenated ligand as it donate its six lone pairs of electrons for the formation of coordinate covalent bonds with metal cations to form Metal-EDTA complex.
Metal-EDTA complex
Metal-EDTA complex

12. Thus it is very important to maintain the pH during
Role of pH in EDTA titrations
EDTA titrations are carried out in buffered solution of
the metal ions to be estimated.
The use of proper pH is important and is related to
the stability constant of a metal-EDTA complex.
E.g. Alkaline pH is required for the metals having
low stability constant.
Low Alkaline to mild acidic pH is required for
the metals having high stability constant.
The dissociation reactions of acid form EDTA, H4Y
are also pH dependant.
pH is also an important criteria for the proper
functioning of the indicator substance.
Thus it is very important to maintain the pH during
the EDTA titrations

13. Advantages of EDTA as titrant: Mn+ + H2Y-2 + H2O MY(n-4) + 2H3O+
ETDA form stable complex with various metal ions.
The complexation occurs in a single step and hence the titration of the metal produce a sharp change in the metal ion concentration at the equivalence point.
3. The Metal-EDTA complexes are all water soluble and hence all studies can be performed in aqueous media.
4. EDTA forms 1:1 complex with all metal ions irrespective of all charge on the metal ions. The stoichiometry is hence same for all metal ions. The reaction can be represented as:
Mn H2Y H2O MY(n-4) H3O+

14. Limitations of EDTA as titrant:
Formation of insoluble hydroxides:
Many ETDA titrations are carried out under alkaline pH which may lead to formation of insoluble hydroxieds or basic salts that may compete with the complexation process .
2. Lack of selectivity:
Since EDTA forms stable complexes with most of the metal ions, it lacks selectivity if it is used to estimate a single metal cations from a solution of mixture of metal ions.

15. Absolute formation constant
EDTA forms 1:1 complex with all metal ions irrespective of all charge on the metal ions. The stoichiometry is hence same for all metal ions.
If fully uprotonated form of EDTA (Y-4) is react with metal ion as follows:
M+n Y MY(n-4)+
Then absolute formation constant KMY is given as,
[MY(n-4)+]
KMY =
eq 1
[M+n] [Y-4]
KMY is also referred as absolute stability constant. Higher
the value of KMY, higher is the stability of complex formed.

16. Group I Group II Titrated in pH 4-8 Group III Titrated in pH 1-4
Metal Cation
KMY
Log KMY
Mg2+
4.9 X 108
8.69
Ca2+
5.0 X 1010
10.70
Sr2+
4.3 X 108
8.63
Ba2+
5.8 X 107
7.76
Mn2+
6.2 X 1013
13.79
Fe2+
2.1 X 1014
14.33
Co2+
2.0 X 1016
16.31
Ni2+
4.2 X 1018
18.62
Cu2+
6.3 X 1018
18.80
Zn2+
3.2 X 1016
16.50
Cd2+
2.9 X 1016
16.46
Al3+
1.3 X 1016
16.13
Pb2+
1.1 X 1018
18.04
Hg3+
6.3 X 1021
21.80
Fe3+
1.3 X 1025
25.1
V3+
7.9 X 1025
25.9
Th4+
1.6 X 1023
23.2
Group I
Titrated in pH 8-11
Group II
Titrated in
pH 4-8
Group III
Titrated in
pH 1-4

17. Conditional formation constant
In absolute formation constant only fully uprotonated form of EDTA (Y-4) is taken consideration. EDTA is tetra protonic acid. It is represented as H4Y. The four different stages of dissociation of this tetra protonic acid can be represented as follows:
H4Y H+ + H3Y-
[H+] [H3Y-]
Ka1 =
= 1.0 X 10-2
[H4Y]
[H+] [H2Y-2]
H3Y H+ + H2Y-2
Ka2 =
= 2.2 X 10-3
[H3Y-]
[H+] [HY-3]
H2Y H+ + HY-3
Ka3 =
= 6.9 X 10-7
[H2Y-2]
[H+] [Y-4]
HY H+ + Y- 4
Ka4 =
= 5.5 X 10-11
[HY-3]

18. CY = [Y-4] + [HY-3] + [H2Y-2] + [H3Y-] + [H4Y]
Each of the equilibrium is pH dependent and Y-4 will predominates only in solution of very high pH.
At lower pH value, the forms of EDTA HY-3 , H2Y-2 ,H3Y-1 , H4Y may also be present. Then the total concentration of uncomplexed EDTA (CY) is given by sum of the all forms of EDTA
CY = [Y-4] + [HY-3] + [H2Y-2] + [H3Y-] + [H4Y]
[H+] [H2Y-2]
[H+] [H3Y-]
[H4Y] =
[H3Y-] =
Ka2
Ka1
[H+] [HY-3]
[H+] [Y-4]
[H2Y-2] =
[HY-3] =
Ka3
Ka4
Substituting the concentrations of the various species in terms of Ka1, Ka2, Ka3, Ka4 in
above equation and solving the equation for the fraction Y-4 form, we get
[Y-4]
Ka1Ka2Ka3Ka4 = CY
[H+] [H+]3 Ka [H+]2 Ka1 Ka [H+] Ka1 Ka2Ka Ka1 Ka2Ka3Ka4

19. [MY(n-4)+] KMY = [M+n] . α4 . CY [MY(n-4)+] = K’MY KMY . α4 =
We may now define α4 as the fraction of EDTA in Y-4 form
[Y-4] or
α4 . CY =
[Y-4]
i.e.
α4 =
eq 2 CY
Substituting equation 1 in equation 2
[MY(n-4)+]
KMY =
[M+n] . α4 . CY
[MY(n-4)+]
= K’MY
KMY . α4 =
[M+n] . CY
K’MY is known as conditional formational constant, or conditional stability constant or effective stability constant

20. Conditional formation constant (K’MY) is product of absolute
formation constant (KMY) and α4 .
K’MY = KMY . α4
The Conditional formation constant (K’MY) is easily calculated
by knowing the absolute formation constant (KMY) and α4
value at the pH of solution.
The Conditional formation constant (K’MY) is greater practical
use because it represents the actual tendency of EDTA to
form the complex with metal at the pH value of the solution.
The values of Conditional formation constant (K’MY) varies with
pH because α4 vary with pH.

21. α4 Values of α4 for EDTA at different pH pH
2.0
3.7 X 10-14
2.5
1.4X 10-12
3.0
2.5X 10-11
4.0
3.3X 10-9
5.0
3.5X 10-7
6.0
2.2X 10-5
7.0
4.8X 10-4
9.0
5.1X 10-2
10.0
3.5 X 10-1
11.0
8.5X 10-1
12.0
9.8X 10-1
As pH increases, α4 values also increases and Conditional
formation constant (K’MY) is also increases

22. Due to such important role of pH in complex
formation with EDTA , normally the solution of metal
ions are buffered so that the pH will remain constant.
In this way the Conditional formation constant (K’MY)
can be estimated and it is possible to calculate and
construct the titration curve from which it is possible
to judge the feasibility of the complexometric titration.
The pH is often adjusted to as low a value as is
consistent with feasibility.
The construction of the titration curve for metal-EDTA
titration can be given as below.

23. Titration curve for metal-EDTA titrations
In the Case of metal-EDTA titration, the EDTA is added to the buffered solution of metal and pM is calculated by using
pM = -log10 [Mn+] during the titration. The obtained pM values is plotted on Y-axis against the volume of EDTA solution added on x axis. This curve give the point of inflexion at the equivalence point. The curve of pM agaist volume of EDTA added is known as Titration curve of metal-EDTA titrations.
Example: Titration curve of Ca+2 with EDTA

24. Example: Titration curve of Ca+2 with EDTA
Absolute formation constant (KMY) for CaY-2 is 5.0 X and
α4 at pH 10 is 0.35.
K’MY = KMY . α4 = 5.0 X 1010 X 0.35 = 1.8 X 1010
Solution:
Take 10 cm3 of 0.01 M ca+2 solution buffered at pH 10 and
titrate with 0.01 M EDTA solution.
Calculate the pCa at different stages of titration such as,
At the start of the titration
After addition of 1.0 cm3 of titrant EDTA
At the equivalence point
After addition of 11.0 cm3 of titrant.

25. At start of Titration:
At start of Titration when no titrant EDTA is added to the solution, only Ca+2 , will be present in the solution.
The concentration of Ca+2 can be given as,
[Ca+2] = 0.01
pCa = -log10 [Ca+2] = -log10 [0.01] = 2.0
pCa = 2.0
2.09

26. 2. At the addition of 1.0 cm3 of titrant:
When 1.0 cm3 of titrant EDTA is added to the solution, 1.0 cm3 Ca+2 will react with EDTA and it will form complex. The 9.0 cm3 of Ca+2 will remained unreacted in the solution and total volume of solution will become 11 cm3.
The concentration of Ca+2 present in the solution can be given as,
[Ca+2] = X 9
pCa = -log10 [Ca+2] = -log10 [0.0082] = 2.09
pCa = 2.09
= M 11

27. 3. At the equivalence point: (when 10 Cm3 of EDTA is added)
When 10.0 cm3 of titrant EDTA is added to the solution, 10.0 cm3 Ca+2 will react with EDTA and it will form complex and total volume of solution will become 20 cm3.
The concentration of Complex [CaY-2] present in the solution can be given as,
[CaY-2] = X 10
At equivalence point, concentration of Ca+2 will be equal to the concentration of EDTA . As EDTA is present in its all form.
So the concentration of EDTA is given by CY
[Ca+2] = CY
= M 20

28. Conditional formation constant (K’MY) for CaY-2 is 108 X 1010,
Now Conditional formation constant (K’MY) is
[CaY-2]
K’MY =
= 1.8 X 1010
[Ca2+]. CY
Since [Ca+2] = CY
[CaY-2]
K’MY =
= 1.8 X 1010
[Ca2+]. [Ca+2]
By substituting,
K’MY = 1.8 X 1010
[CaY-2] = 0.005
In the above equation and we can calculate the concentration of [Ca2+]

29. 0.005
1.8 X =
[Ca2+]2
0.005
[Ca2+] =
1.8 X 1010
[Ca2+] =
5.2 X 10-7
pCa = -log10 [Ca+2] = -log10 [5.2 X 10-7] = 6.28
pCa = 6.28

30. 4. After the addition of 11 Cm3 of EDTA:
When 11.0 cm3 of titrant EDTA is added to the solution, 10.0 cm3 Ca+2 will react with EDTA and it will form complex and 1.0 cm3 of EDTA will remain excess in the solution. Total volume of solution will become 21 cm3.
The concentration of Complex [CaY-2] present in the solution can be given as,
[CaY-2] = X 10
= X 10-3 M 21

31. The 1.0 cm3 of EDTA is excess,
concentration of excess of EDTA present in the solution can be given as,
[Excess of EDTA] = X 1
The concentration of EDTA in the solution given by CY
= X 10-4 M 21
CY = X 10-4 M

32. Conditional formation constant (K’MY) for CaY-2 is 1.8 X 1010,
Now Conditional formation constant (K’MY) is
[CaY-2]
K’MY =
= 1.8 X 1010
[Ca2+]. CY
By substituting,
K’MY = 1.8 X 1010
[CaY-2] = 4.76 X 10-3
[CY] = 4.76 X 10-4 M
In the above equation and we can calculate the concentration of [Ca2+]

33. 4.76 X 10-3
1.8 X =
[Ca2+] X 4.76 X10-4
4.76 X 10-3
[Ca2+] =
1.8 X 1010 X 4.76 X10-4
[Ca2+] =
5.55 X 10-10
pCa = -log10 [Ca+2] = -log10 [5.55 X 10-10] = 9.26
pCa = 9.26

34. Volume in Cm3 of 0.01 M EDTA added
Table of pCa Value
Volume in Cm3 of 0.01 M EDTA added
pCa
0.0
2.0
1.0
2.09
5.0
2.48
10.0
6.28
11.0
9.26
12.0
9.56
When the pCa is plotted against volume of titrant added, it gives the Familiar S shaped titration curve with sharp increse in the curve in the value of pCa in the vicinity of the equivalence point.

35. Titration curve for Ca+2 - EDTA titrations
pCa
Volume of 0.01 M EDTA added

36. Types of EDTA Titrations:
Direct
Titrations
Back
Titrations
Replacement/
Displacement/
Substitution
Titrations
Alkalimetric
Titrations
Indirect
Titrations

37. Metal ion + EDTA [ Metal-EDTA ] complex
Direct Titrations:
This is a direct determination of a metal ion by adding
standard EDTA titrant to the sample solution.
Metal ion + EDTA [ Metal-EDTA ] complex
The solution containing the metal ion is buffered to the desired
pH and titrated directly with standard EDTA solution.
Some auxiliary complexing agent such as tartarate can be
added to prevent the prevent the precipitation of the hydroxide
of metal ion.
Cu+2, Zn+2, and Ni+2 can be determine by using direct
titration method. +

38. This is method, an excess of standard EDTA is added to the
Back Titrations:
This is method, an excess of standard EDTA is added to the
sample solution of metal ion.
The resulting solution will contain unreacted EDTA which is
then back titrated with standard metal ion solution in the
presence of indicator.
ZnCl2, ZnSO4, MgCl2, MgSO4 is used as standard metal ion
solution.
Al+3, Co+2, Pb+2, Mn+2, Hg+2, and Ni+2 can be determine by
using Back titration method

39. Back Titration Process+ +
Sample
Metal
ion M1
Excess of
standard EDTA
Metal-EDTA
Complex
M1-EDTA
Unreacted
standard EDTA
Standard
Metal ion M2
Metal-EDTA
Complex
M2-EDTA

40. This is method, weak EDTA complex of another metal ion (M2)
Replacement, Displacement or Substitutions Titrations:
This is method, weak EDTA complex of another metal ion (M2)
is added to the solution of metal ion (M1) to be determined.
Mg-EDTA & Zn-EDTA are frequently used weak EDTA complex
The weaker metal EDTA complex is replaced with strong metal
EDTA complex.
The equivalent amount of metal M2 freed from the weaker
complex can be titrated with standard EDTA solution.
This method is useful for the determination of Ca+2 ion.

41. Replacement, Displacement or Substitutions Titrations Process+ +
Replaced
Free metal
ion M2
Weak
Metal-EDTA
Complex
M2-EDTA
Strong
Metal-EDTA
Complex
M1-EDTA
Sample
Metal
ion M1
Standard
EDTA solution
Metal-EDTA
Complex
M2-EDTA

42. Alkalimetric Titrations:
This method, use the principle of liberation of free H+ ions
during the complexation.
The reaction between metal ion and EDTA H2Y-2 produce H+.
M+n H2Y MY(n-4) H+
The free H+ ions is titrated with standard solution of alkali like
NaOH by using suitable acid-base indicator.
The H+ ions can also be determined by instrumental method.

43. Alkalimetric Titrations Process+ +
2H+
Sample
Metal
ion M+n
standard EDTA
H2Y-2
Metal-EDTA
Complex
MY(n-4)+
Liberated H+
ions
NaOH
Standard
Alkali solution
Acid-Base
Titration product

44. Indirect Titration:
This method is used to determine the ions such as Halides, phospates, and sulphates that do not form complex with EDTA .
In the determination of sulphate ion, SO4-2 ion solution is treated with excess of standard solution of Barium ion.
The formed precipitate of BaSO4 is filtered off and unreacted Barium ions present in filtrate is titrated with EDTA.
In this way, we are able to indirectly determine the amount of sulphate ion present in the sample solution.

45. Indirect Titrations Process+ +
Ba+2
Anions like SO4-2
Excess of
standard Barium
solution
BaSO4
Precipitate
Unreacted Ba+
ions
Standard
EDTA solution
Ba-EDTA
Complex

46. Methods of increasing the selectivity of EDTA as Titrations
Chemical
Separation pH
Control
Masking
Unmasking
Kinetic
Masking

47. Chemical Separation In this technique, the selectivity is increases by
separating the species from other components from the
sample solution.
The separated species is then dissolved in suitable
solvents and then titrated against EDTA using indicator.
Eg: Ca+2, Mg+2, Ni+2 and Cu+2 ions can be first separated as
Ca-oxalate, Ni-DMG, Mg-ammonium phosphate and
Cu-thiocyanide.
These precipitate are then dissolved in separate suitable
solvents and then titrate against EDTA using indicator.

48. Chemical Separation precipitate Precipitate precipitate precipitate
Mg+2
Ni+2
Cu+2
Ammonium
phosphate
DMG
thiocyanide
Oxalate
Ni-DMG
precipitate
Mg-ammonium
Phosphate
Precipitate
Cu-thiocyanide
precipitate
Ca-oxalate
precipitate

49. EDTA EDTA EDTA EDTA Ca-EDTA Ni-EDTA Mg-EDTA Cu-EDTA Ca-oxalate Ni-DMG
Mg-ammonium
phosphate
Cu-thiocyanide
solvent
Ca+2
solvent
Ni+2
solvent
Cu+2
solvent
Mg+2
EDTA
EDTA
EDTA
EDTA
Ca-EDTA
Ni-EDTA
Mg-EDTA
Cu-EDTA

50. Control of acidity of pH of the solution
In this technique, the selectivity is increases by
controlling the pH of the solution.
The conditional formation constant for metal-EDTA
complex is depend on the hydrogen ion concentration.
So by adjusting the pH of the sample solution containing
several metal ions, it is possible to allow only a single
species to react with EDTA.
E.g.: Ca+2 can be determined in the presence of Mg+2 in
strongly alkaline solution (pH < 10).
Trivalent ions loke Bi+3, Fe+3 can be selectively
determined from the solution of bivalent metal ions in
strongly acidic solution (pH ~ 2.

51. Selectivity by pH Control
A+2
B+2
A+2
B+2
Ca+2
Mg+2
Fe+3
Bi+3
EDTA
At Alkaline
pH < 10
EDTA
At Alkaline
pH ~2
EDTA
At Alkaline
pH ~2
Metal-EDTA
Complex
Ca-EDTA
Metal-EDTA
Complex
Fe-EDTA
Metal-EDTA
Complex
Bi-EDTA

52. Use of Masking agent
Masking is a process in which substance is prevented to
take part in the reaction without physical separation of it.
The reagent used in masking is known as masking agent.
Cyanide ion is an effective masking agent for EDTA
titrations. It forms stable cyanide complex with the metal
cation like Cd, Zn, Hg, Cu, Co, Ni, Ag, Pt but does not form
complex with alkaline earth metals like Mg, Ca etc as well
as Mn and Pb.
Thus it is possible to determine Ca, Mg, Pb, Mn in the
presence of other metal cations by masking agents like
CN- ion

53. Masking CN- Ca+2 ions Zn-CN complex Hg-CN complex Ni-CN complex Ca+2

54. Prevented to take part in reaction
Masking
CN-
Ca+2
ions
Zn-CN
complex
Hg-CN
complex
Ni-CN
complex
EDTA
Masked complexes
Prevented to take part in reaction
Metal-EDTA
Complex
Ca-EDTA

55. Use of Demasking
In this technique, the one of the cation is first masked
and remaining free cation is titrated with standard EDTA.
Then previously masked cation is demasked by using
suitable reagent to get free cation.
This free cation is then titrated by using standard EDTA.
eg. Formaldehyde is used to demasked Zn-CN complex
[Zn(CN)4] + 4HCHO H Zn HOCH2CN
This free Zn+2 ion is then titrated by using standard EDTA.
Thus it is possible to determine Zn in the presence of Ca.

56. Demasking
Ca+2
Zn+2
Masking
CN-
Ca+2
ions
Zn-CN
complex

57. Ca+2 ions Zn-CN complex Demasking Zn+2 ion
EDTA
Zn+2 ion
EDTA
Metal-EDTA
Complex
Ca-EDTA
Metal-EDTA
Complex
Zn-EDTA

58. Kinetic masking Some of the metal undergoes fast complexation some of
undergoes slow complexation with EDTA .
Hence it is possible to titrate the metal ions which
undergoes fast complexation with EDTA in the presence
of those metal ions which undergoes slow complexation
with EDTA .
eg. Fe+3 can be easily estimated in the presence of Cr+3 ,
because Cr+3 reacts slowly with EDTA to form complex as
compared to Fe+3.

59. Kinetic masking EDTA- EDTA- FAST- SLOW Metal-EDTA Metal-EDTA Complex
Fe+3
Cr+3
EDTA-
EDTA-
FAST-
SLOW
Metal-EDTA
Complex
Cr-EDTA
Metal-EDTA
Complex
Fe-EDTA

60. Metallochromic indicator Theory and Applications

61. Metallochromic indicator
The metallochromic indicators are organic compounds
which are capable of forming intensely coloured
complex with EDTA.
This metal –indicator complex is weaker than the
Metal-EDTA complex and it has different colour than
uncomplexed indicator.
During the course of titration, the metal ion from
metal –indicator complex is replaced to form
Metal-EDTA complex.

62. Metallochromic Indicator+
Sample
Metal
ion
Indicator
Organic
Compound
Colour 1
Metal-Indicator
Weak Complex
Colour 2
EDTA
Metal-Indicator
Strong Complex
Colour 3

63. Requirement for Metal ion indicator
1. The colour must be sufficiently intense, so that a
minimum amount of indicator can be used.
The colour contrast between the indicator and
Metal-indicator complex should be readily observable.
The Metal-indicator complex should possess sufficient stability to ensure a sharp colour change, however it should be less stable than Metal-EDTA complex.
The change in equilibrium from metal-indicator complex to the Metal-EDTA complex should be sharp and rapid.

64. The colour reaction of the indicator should be
selective.
The indicator must be very sensitive to metal ions so that the colour change occurs at near the equivalence point.
The indicator must be stable in the titration medium.
The indicator must be stable on storage also.
All the above requirements must be fulfilled in the pH range in which the proposed titration is to carried out.
It should be commercially available in adequate purity.

65. Theory of metal ion indicators

66. M-In + EDTA M-EDTA + In M + In M-In
The reaction corresponding to use of a metal ion indicator in an EDTA titration can be represented as
M-In + EDTA M-EDTA In
This reaction will take place only if the M-EDTA complex is more stable than the M-In complex.
M In M-In
Stability of the Metal-Indicator complex KIn, is given by the equation
[M-In]
KIn =
[M] [In]

67. Since, the indicator colour change also affected by the hydrogen ion concentration, so it is convenient to define the conditional indicator constant K’In which varies with pH.
For small the error, K’In > 104 and the ratio of conditional formation constant of the metal-EDTA complex K’MY to K’In should be of the order 104 to provide a good end point.

68. use of metal ion indicators

69. Examples Of metal ion indicators

70. Eriochrome Black T
Chemically it is sodium salt of 1-(1-hydroxy-2 naphthylazo)-6 nitro-2-naphthol-4-sulphonic acid.
2. It is dark powder with a slight metallic luster

71. 3. Eriochrome Black T (EBT) is abbreviated as H3D in strongly acidic medium.
4. In basic pH it is present in dissociated form and abbreviated as H2D-, HD-2 and D-3.
5. Different form and colour of EBT can be summarised as follows:
EBT
Acidic pH
H3D
Black
pH- 6
H2D-
Red
pH- 7-11
HD-2
Blue
pH > 12
D-3
Orange

72. In EDTA titrations, BDT forms red colour Metal-EDTA weak red colour complex complex . As titration begins, EDTA will replace indicator ion and it will form strong
Metal-EDTA blue colour complex.
Metal –
EDTA
Strong
Blue colour
Complex
Metal –
Indicator
Weak
Red colour
Complex
EDTA
Metal +
Indicator
So, end point with EBT indicator is Red to blue.

73. EBT Indicator EDTA + Sample Metal ion EBT Indicator Metal-Indicator
Weak Complex
Red Colour
EDTA
Metal-Indicator
Strong Complex
Blue Colour

74. EBT is used to estimate Mg, Zn, Mn, Cd, Hg, Pb, Cu, Al, Fe, Ti, Co, Ni and Pt metal ions in Back and replacement EDTA titrations.
The indicator is prepared by dissolving 0.2 gm of the EBT powder in 15 ml of triethanolamine followed by the addition of 5 ml of absolute alcohol

75. Murexide
Chemically it is ammonium salt of purpuric acid. It’s single charged ions has the following structure.
2. It is pinkish brown powder

76. Different form and colour of EBT can be summarised as follows:
Indicator pH
Colour
Murexide
Up to pH 9
Reddish violet
pH- 9-11
Violet
pH > 11
Blue Violet

77. So end point of the titration using Murexide indicator is+
Sample
Metal
ion
Murexide Indicator
Metal-Indicator
Weak Complex
Red Colour
EDTA
Metal-Indicator
Strong Complex
Blue violet Colour
So end point of the titration using Murexide indicator is
Red to Blue violet

78. Murexide is used to estimate Ca, Ni, Co, Zn, Cd, Cu metal ions in EDTA titrations.
The indicator is prepared by dissolving Merexide powder in water. Aqueous solution of murexide is unstable hence it must be prepared freshly.

79. Pyrocatechol violet
Pyrocatechol violet is used to estimate Al, Bi, Cd, Co, Cu, Ga, Fe, Pb, Mg, Mn, Ni, Th, Ti, Zn metal ions in EDTA titrations.

80. Xylenol orange
Xylenol orange is used to estimate Bi, Cd, Pb, Sc,Th, Zn metal ions in EDTA titrations.

81. Pyridylazonaphthol (PAN)
Pyridylazonaphthol (PAN) is used to estimate Cd, Cu, In, Sc, Zn, metal ions in Back and replacement EDTA titrations.

82. Thank You
And
Best of Luck