The document discusses complexometric titrations, specifically using EDTA as a titrant for estimating metal ions in various applications, including pharmaceuticals and environmental science. It covers indicators, stability of complexes, titration techniques (direct, back, and replacement), and the use of masking and demasking agents. Additionally, it provides detailed methods for preparing solutions, standardizing EDTA, and specific procedures for assays of calcium gluconate and magnesium sulfate.

1. Mrs Vandana Sharma
Assistant Professor

3.  Classification
 Metal ion ion indicators
 Masking and demasking reagents
 Estimation of Magnisium sulphate
 Calcium gluconate

4.  2017
 What is are different indicators used in complexometric
titrations? How the stability of complex decided. 10
 Give the principle and procedure for assay of calcium
gluconate. 6
 Give the principle and procedure for assay of
 Magnisium sulphate. 5
 2011
 Describe ligands and Chelets with suitable example. 8
 Give the principle and procedure for assay of calcium
gluconate. 8
 2012
 Write a detail account of the principles involved in
complexometric titrations using the suitable example of
pharmaceutical product. 8
 Write a note on the indicators used in complexometric
titrations. 8

5.  March/April-2013
 Short Note- Principle of standarization of disodium edetate.
4
 Give a brief account of stability of complexs and
metallochrome indicators. 4,3
 Explain the different types of E.D.T.A titrations. 9
 August/September- 2013
 Write down the assay procedure of the following:-
 Calcium gluconate by complexometry
 Magnisium sulphate by Gravimetry
 March/April 2014
 A) How will you estimate the amount of calcium gluconate
and magnesium sulphate in a mixture of by complexometric
titration?
 How will you prepare 0.1m standard solution of EDTA
 Write Short note on the following-
Discuss about effect of pH on titration with EDTA. 4

6.  March/April-2012
 Write a detailed account of the principles involved in
complexometric titrations using a suitable example of
pharmaceutical product. 8
 Write a note on the indicators used in complexometric
titrations. 8

7.  Complexometric Titration, also known as chelatometry, is
a volumetric analysis in which the endpoint of the titration
is determined using a coloured complex.
 Titration is a common technique used in labs to determine
the concentration of an unknown analyte.
 Complexometric Titration involves the formation of a
complex between a chelating agent and a metal ion.
 The complex is then titrated with a standardized solution of
EDTA.
 Complexometric titration is used in the fields of
environmental science and medicine for precise
measurements of metal ion concentrations.
 Some commonly used chelating agents include
ethylenediaminetetraacetic acid (EDTA),
diethylenetriaminepentaacetic acid (DTPA), and
nitrilotriacetic acid (NTA).
 It is a powerful analytical technique that enables researchers
to accurately measure metal ion concentrations in a wide
range of applications.

8.  Complexometric titration is used for the
estimation of the amount of total hardness in
water.
 It is widely used in the pharmaceutical
industry to determine the metal
concentration in drugs.
 Titanium dioxide is used in many cosmetic
products. This can be analysed by
complexometric titration.
 It is used to analyse urine samples.
 It is widely used in analytical chemistry.

9. EDTA can be used as a chelating titrant (titrant can be defined
as the solution whose concentration is known in the titration)
in many ways.
EDTA titrations can be performed in many ways. A few of them
are given as follows –
 Direct Titration
 Back Titration
 Replacement Titration
 Indirect Titration

10.  Direct Titration –
It is the most convenient and simple method of complexometric
titration using EDTA.
 It is similar to the acid–base titration technique.
 In this titration standard, EDTA solution is added to give sample
containing metals using burette till the endpoint is achieved.
 Copper, barium, zinc, mercury, aluminium, lead, bismuth, chromium,
etc. are metals that can be determined by using direct
complexometric titration.
Example-
Calcium gluconate injection, Calcium lactate tablets and compound.
Ca+2 + EDTA------Ca-EDTA
Limitation-
Direct titration method cannot be applicable for slow complexation
reaction
Because of interference due to the precence of other ions

11.  Back Titration –
 An excess amount of standard solution of EDTA is added to the
metal solution being examined.
 Then the excess amount of EDTA is back titrated by the solution of
the second metal ion.
Example-
Mn+2 + EDTA(In Excess)----Mn-EDTA + EDTA( Remaining)
EDTA (Remaining) + Zn+2-----Zn-EDTA
Determination of Mn+2-
An excess of known volume of EDTA is added to an acidic
solution of Mn salt and then add ammonia buffer is used to
adjust the pH to 10-------Excess of EDTA remaining after
chelation is back titrated with standard Zn solution kept in
burette using eriochrome black T as indicator

12.  Replacement Titration –
It is used when direct titration or back titration don’t give sharp endpoints.
This analyte (containing metal) is added to the metal–EDTA complex. The
metal present in the analyte displaces another metal from the metal–EDTA
complex.
Example
Mn+2 + Mg-EDTA-2------- Mg+2 + Mn-EDTA-2
(Analyte) (in excess quantity) (Free) (More stable Complex)
Mg+2 + EDTA-4-----------------Mg-EDTA-2
(Free) (directly titrated with)
• Mn+2 displaces Mg-EDTA solution
• the free Mg metal is then directly titrated with standard EDTA solution
• In this method, excess quantity of Mg-EDTA complex is added to Mn+2
solution
• Mn+2 quantitively displaces Mg+2 from Mg-EDTA complex
• This displacement takes place because Mn+2 form a more stable
complex with EDTA
• Using this method Ca+2, Pb+2, Hg+2 can also be determined
• Indicator- Eriochrome black T

13.  Indirect Titration/Alkalimetric titrations –
 Example- Barium ions, Barbiturate
 Barbiturate + EDTA-4 ---------- No reaction
 Its is used for determination of such anions ------ Which do not react
with EDTA. Eg. Barbiturate will not react directly with EDTA.
 But barbiturate forms complex with Hg+2 ions quantitatively.
 Barbiturate-Hg(complex) + EDTA-4 -------- Hg-EDTA-2 + Barbiturate
 Titration of Hg-barbiturate with EDTA gives the concentration of
equivalent amount of barbiturate (proton from Disodium EDTA are
displaced by a Heavy metal)

14.  Masking agent – Masking agent may be defined as process --
---in which a substance-----without physical separation of
it or its reaction products ----- so transformed ----- that it
is does not participate in a reaction.
In simple words- its reaction is masked
Or
 Masking is a reagent----that protects some component of
analyte---- from reaction with EDTA
 Making used to prevent one element ----- from interfering
in the analysis of another element.
 Masking agent acts either by
1. Precipitation
2. Formation of complexes that are more stable than
the interfering ion-EDTA complex

15.  Masking agent form more stable complexes with the
interfering metal ions
 Masking agents must not form complex with the metal ion
under analysis
Examples
Ammonium fluoride( NH4 F) - form complex with Al+3
(Aluminium), Fe+3(Iron), Ti+3 (Titanium)
Ascorbic Acid(C6H8O6)- very good masking agent for Fe+3
Dimercaprol or 2,3- dimercptopropanol
act as complexing agent for most of metal ion. Eg- Hg+2, Cd+2,
Zn+2, Cu+2, Ca+2, Mg+2, Pb+2, Sn+2
Potasssium cyanide(KCN) – React with metal ion and form more
stable complex with in alkaline solution as compare with EDTA-
metal complex (Hg+2, Ag+2, Zn+2, Cu+2, Cd+2)

16. Potassium iodide (KI)- Hg+2(only specific for mercury ions)
Tiron (disodium catechol-3,5-disulponate) – Al+3,
Ti+3(Titanium)
Triethanolamine Al+3, Ti+3

17.  Demasking Agents- is reagent----- that release of metal
ion ------ from a masking agent
OR
Are reagents which regain the ability of masked ion to
enter the reaction with indicator and EDTA.
Examples
Formaldehyde- used to demask the Cyanide complexes of
Cadmium and Zinc----after demasking, metal ion can be
determined by titrating with EDTA
Chloral hydrate- same as formaldehyde
Methanol-acetic acid complex- same as above. Ratio b/w
methanol and acetic acid (3:1)
Solvent extraction method- used to separate Zinc from
mixture of lead and copper.
Add Ammonium thiocyanate solution in the mixture
solution-----Zinc form complex as Zinc thiocyanate

19. In acid base titration – indicators are responsive to H+ ion
concentration
In complexometric titrations- indicators are responsive to the
metal ions like Mg, Ca, Cu etc
Indicators of complexometric titration----forms coloured complex
with metal ions----and color is different when complexing agent
form complex with metal ions
Example-
 Eriochrome black T/Solochrme black T/Mordant black II or EDT
 Calmagite- can be used as replacement of Eriochrome black T
indicator
 Murexide
 Xylenol orange
 Calcon
 Catechol violet

20. Complexometric Indicators
Calmagite and Eriochrome BlackT (EBT) are examples of
indicators that change colour from blue to pink when calcium or
magnesium is present.
When the colour changes from pink to blue, the endpoint of a
complexometric EDTA titration utilising either Calmagite or EBT
as the indicator has been reached.
Some commonly used complexometric indicators include
Eriochrome Black T, Calmagite, Xylenol Orange, Murexide, and
Ferroin.
In a complexometric titration, there are two approaches for
detecting the endpoint.

21.  Visual Technique
 Due to its simplicity, low cost, and precision, the visual
technique is one of the most often used methods for
determining endpoints.
 Some of the visual approaches for finding the end point of
complexometric titrations are listed below.
 PM indicators (metallochromic)
 Indicators of pH
 Redox Indicators
 Instrumental Techniques
 The visual methods for determining the endpoint have
limitations, such as
 inaccuracy and human visual errors.

22.  The following are some of the instrumental approaches used
in endpoint determination.
 Photometry
 Potentiometry
 Miscellaneous methods.
 The choice of the complexometric indicator depends on the
metal ion being analyzed.
 This is because different indicators have different sensitivity
and selectivity for different metal ions.
 A proper selection of the indicator is necessary to ensure
accurate results in complexometric titration.

23.  Complex titration with EDTA.
 EDTA, ethylenediaminetetraacetic acid, has four carboxyl groups
and two amine groups that can act as electron pair donors, or
Lewis bases.
 The ability of EDTA to potentially donate its six lone pairs of
electrons for the formation of coordinate covalent bonds to metal
cations makes EDTA a hexadentate ligand.
Note-
 However, in practice EDTA is usually only partially ionized, and
thus forms fewer than six coordinate covalent bonds with metal
cations.
 Disodium EDTA is commonly used to standardize aqueous
solutions of transition metal cations.
 Disodium EDTA (often written as Na2H2Y) only forms four
coordinate covalent bonds to metal cations at pH values ≤ 12.

24.  In this pH range, the amine groups remain protonated and
thus unable to donate electrons to the formation of
coordinate covalent bonds.
 Note that the shorthand form Na4−xHxY can be used to
represent any species of EDTA, with x designating the
number of acidic protons bonded to the EDTA molecule.
 EDTA forms in aqueous solution. an octahedral complex with
most 2+ metal cations, M2+,
 The main reason that EDTA is used so extensively in the
standardization of metal cation solutions is that the
formation constant for most metal cation-EDTA complexes is
very high, meaning that the equilibrium for the reaction:
 M2+ + H4Y → MH2Y + 2H+ lies far to the right.
 Carrying out the reaction in a basic buffer solution removes
H+ as it is formed, which also favors the formation of the
EDTA-metal cation complex reaction product.
 For most purposes it can be considered that the formation of
the metal cation-EDTA complex goes to completion, and this
is chiefly why EDTA is used in titrations and standardizations
of this type.

25.  Principle-
 Complexometric / chelatometry titration – a from of volumetric analysis-
----- in which the formation of a colored complex ---- indicate the
endpoint of a titration.
 Complexometric titrations------ particularly useful for the determination
of mixture of different metal ions in solution.
 An indicator capable of producing a clear color change at end point is
used.
 Eg- --Ca+2/Mg+2 + Eriochrome black T/ Mordant black II (Indicator)
(Wine Red Color)
Titrant- Ethylene diamine tetra acetic acid/EDTA
Ca-EDTAComplex/Mg-EDTA Complex + Free Mordant black II indicator
(Final color at the end point is blue)

26. Preparation of Reagents
Preparation of 0.05M disodium edetate.2H2O
Molarity= No. of moles of solute (n)
Volume of solution (L)
No. of moles of solute= weight in gram of solute
Molecular wt of solute
Molarity= weight in gram of solute/molecular wt of solute
Volume of solution in liter
1 = ? / 372.24 =
1
Weight in gram of solute (Disodium edetate dihydrate)= 372.24g
in 1000ml or 1liter
For 0.05M= 372.24 x 0.05= 18.612g di sodium edetate dissolve in
1000ml of water

27. Preparation of Bromine water-
3ml Br2 + few ml distlled water----- make up final volume upto 100ml
Preparation of 2N NaOH
Normality = No. of gram equivalent of solute
Volume of solvent in liter
No. of gram equivalent of solute= Molecular weight
(n)Acidity of base
N= No. of hydrogen atoms in acid or no. of hydroxide atoms in base or
valency of salt
Normality= Molecular weight /Acidity of base
Volume of solvent in liter
For 1N NaoH dissolve 40g NaOH in CO2 free distilled water upto 1000ml
For 2N NaOH solution of 8g accuretly weigh NaOH upto 100ml free
distilled water

28. Preparation of ammonia buffer (pH=10)
5.4gm accurately weigh NH4Cl in 70ml 5N ammonia and dilute
with 100ml distilled water
5N ammonia
Ammonium Hydroxide Solution, 1 N: Add 5 X 66 mL = 330ml of
concentrated ammonium hydroxide (28% NH4OH, sp g 0.90) to 500
mL of purified water and dilute to 1 L volume.
Dilute HCl
Add 8.26 mL of concentrated HCl to about 50 mL of distilled water, stir,
then add water up to 100 mL.

29. Procedure of standaridization
1. Accurately weigh 0.8 g granulated Zn + 12ml dilute HCl----by
gently warming + 5drops of bromine water ---- warm the solution
till the boiling
2. Boiling helps----to remove excess amount of bromine----- +
with distilled water produce upto 200ml
3. Conical flask---- 20ml Above solution (Pipette out) + 2N NaOH
(to neutralization of solution --- monitor by pH paper)------ Dilute
the neutralzed solution upto 150ml ( if any precipitate is present
then add ammonia buffer solution till ppt is dissolved) + 5ml buffer
solution in excess + 3-4 drops of Mordant black-II /
Eriochrome Black T / Solochrome black inicator solution
turns blackish blue color
4. Burette----Sodium edetate solution
5. End point--- Blackish Blue to light green

30. 0.05 M EDTA
20ml of Zn solution +
Ammonia buffer (pH= 10+
Mordant Black II ( 3-4 drops)
End point ---- Blackish Blue
light Green color
Standardization of EDTA

31. Estimation of magnesium sulphate
0.05 M EDTA
20ml of Zn solution +
Ammonia buffer
(pH= 10)+
Mordant Black II ( 3-4
drops)
End point –
Blackish Blue to
light Green color
Standardized EDTA solution
0.3g MgSO4.7H2O+
50ml distilled water+
10ml Buffer+ Mordant
Black II
Step -1
standardization of EDTA
Step -2
Estimation of magnesium sulphate
End point –
Blue color to Pink
color

32.  Principle-
 Complexometric / chelatometry titration – a from of volumetric analysis-
----- in which the formation of a colored complex ---- indicate the
endpoint of a titration.
 Complexometric titrations------ particularly useful for the determination
of mixture of different metal ions in solution.
 An indicator capable of producing a clear color change at end point is
used.
 Eg- --Ca+2/Mg+2 + Eriochrome black T/ Mordant black II (Indicator)
(Wine Red Color)
Titrant- Ethylene diamine tetra acetic acid/EDTA
Ca-EDTAComplex/Mg-EDTA Complex + Free Mordant black II indicator
(Final color at the end point is blue)

33. Preparation of Reagents
Preparation of 0.05M disodium edetate.2H2O
Weight in gram of solute (Disodium edetate dihydrate)= 372.24g in
1000ml or 1liter
For 0.05M= 372.24 x 0.05= 18.612g di sodium edetate dissolve in 1000ml
of water
Preparation of Bromine water-
3ml Br2 + few ml distlled water----- make up final volume upto 100ml
Preparation of 2N NaOH
For 1N NaoH dissolve 40g NaOH in CO2 free distilled water upto 1000ml
For 2N NaOH solution of 8g accuretly weigh NaOH upto 100ml free
distilled water
Preparation of ammonia buffer (pH=10)
5.4gm accurately weigh NH4Cl in 70ml 5N ammonia and dilute with
100ml distilled water
5N ammonia
Ammonium Hydroxide Solution, 1 N: Add 5 X 66 mL = 330ml of
concentrated ammonium hydroxide (28% NH4OH, sp g 0.90) to 500 mL of
purified water and dilute to 1 L volume.
Dilute HCl
Add 8.26 mL of concentrated HCl to about 50 mL of distilled water, stir, then
add water up to 100 mL.

34. Procedure of standarization of EDTA
1. Accurately weigh 0.8 g granulated Zn + 12ml dilute HCl----by
gently warming + 5drops of bromine water ---- warm the solution
till the boiling
2. Boiling helps----to remove excess amount of bromine----- +
with distilled water produce upto 200ml
3. Conical flask---- 20ml Above solution (Pipette out) + 2N NaOH
(to neutralization of solution --- monitor by pH paper)------ Dilute
the neutralzed solution upto 150ml ( if any precipitate is present
then add ammonia buffer solution till ppt is dissolved) + 5ml buffer
solution in excess + 3-4 drops of Mordant black-II /
Eriochrome Black T / Solochrome black inicator solution
turns blackish blue color
4. Burette----Sodium edetate solution
5. End point--- Blackish Blue to light green

35.  Calculations= to calculate the actual molarity of EDTA
Molecular weightof Zn= 65.38u
ZnCl2= Zn+2= 1000ml M
65.38g Zn= 1000ml M
(65.38 X 0.05= 3.269) g Zn= 1000ml 0.05 M
0.003269g Zn = 1ml of 0.05M disodium ethylenediaminetetracetate
0.08g Zn is present in 20 ml EDTA
0.08 = 24.47 ml 0.05M EDTA
0.003268
Actual molarity of EDTA= 0.05 X 24.47
Volume of EDTA consumed

36.  ESTIMATION OF MAGNESIUM SULPHATE
 Magnesium sulphate heptahydrate : 0.3 g
 strong ammonia-ammonium chloride solution (6.75 g NH4Cl in 74.0 ml
strong ammonia solution add water q.s. to produce to 100 ml) ;
 0.05 M disodium edetate ;
 Mordant Black II mixture (mixture of 0.2 part mordant black II with 100
parts of NaCl): 0.1 g.
EQUATIONS :
The assay of MgSO4.7H2O is based upon the reactions designated by
the following equations:
Mg2+ + [H2X]2-–→[MgX]2– + 2H+
or MgSO4.7H2O≡ Mg2+ ≡ Na2H2X, 2H2O
or120.38 g MgSO4 ≡ 20,000 ml 0.05 M
or 0.00602 g MgSO4 ≡ 1 ml of 0.05 M Disodium Edetate

37.  PROCEDURE : •
 Conical Flask--Weigh accurately about 0.3 g of magnesium
sulphate heptahydrate and dissolve in 50 ml of DW. Add to it 10
ml of strong ammonia-ammonium chloride solution, and 0.1 g of
mordant black II mixture as indicator
 Burette--titrate with 0.05 M disodium ethylene diamine tetracetate
 End Point--The pink colour is discharged from the blue.
Each ml of 0.05 M disodium ethylene diamine tetracetate is
equivalentto 0.00602 g of MgSO4.
 Result– The parcentage purity of given sample of Magnesium
sulphate was found to be X %

38.  C12H22CaO14H2O
 Molecular weight 448.4
 Calcium gluconate is a calcium o-gluconate
monohydrate.
 Calcium gluconate contains not less than 98.5
per cent and not more than 102.0 per cent of
C12H22CaO14H2O.
 Category: Calcium replenisher.
Apparatus: Beaker, Funnel, Pipette, Burrette.
Chemicals: Magnesium sulphate, Strong ammonia solution,
Calcium gluconate.

39.  Procedure
 (A) Standardisation of 0.05M Disodium EDTA:
 Preparation of disodium EDTA (0.05M): Dissolve 37.2 g of disodium
EDTA + water to produce 1000 ml.
 For 0.05M= 372.24 x 0.05= 18.612g di sodium edetate dissolve in
1000ml of water
 Procedure: Weigh accurately about 0.8 g of granulated zinc + dissolve
by gentle warming in 12 ml of dilute hydrochloric acid + add 0.1 ml of
bromine water. Boil (to remove excess bromine), cool and + water to
produce 200.0 ml.
 Conical flask-Pipette out 20.0 ml of the resulting solution into a flask and
nearly + neutralize with 2 M sodium hydroxide. Dilute to + about 150 ml
with water, + sufficient ammonium buffer (of pH 10.0 ) to dissolve the
precipitate and add 5 ml in excess ammonia buffer. + 50 mg of Mordant
Black II mixture and
 Burette- titrate with disodium EDTA solution
 End point--Until the solution turns green.
 1 ml of 0.1 M disodium EDTA is equivalent to 0.000654 g of Zn.

40.  (B) Assay:
 Conical Flask-Weigh accurately about 0.5 g calcium gluconate and
dissolve in 50 ml of warm water; cool, add 5.0 ml of 0.05 M
magnesium sulphate and 10 ml of strong ammonia solution and
mordant black II mixture as an indicator
 Burette --Titrate with 0.05 M disodium EDTA using.
 From the volume of 0.05 M, disodium EDTA is required to
subtract the volume of magnesium sulphate solution added.
 1 ml of the remainder of 0.05 M disodium EDTA is equivalent to
0.02242 g of C12H22CaO14H2O.
Result : the percentage purity of given sample of calcium gluconate
was found to be x%

41. Estimation of calcium gluconate
0.05 M EDTA
20ml of Zn solution
+
Ammonia buffer
(pH= 10)+
Mordant Black II ( 3-
4 drops)
End point –
Blackish Blue to
light Green color
Standardized EDTA solution
0.5 g calcium gluconate +
50 ml of water + 5.0 ml
of 0.05 M magnesium
sulphate 10 ml of strong
ammonia solution +
Mordant Black II
Step -1
standardization of EDTA
Step -2
Estimation of calcium gluconate
End point –
Deep Blue

42.  Complexometric titration is a widely used analytical technique
that has multiple applications such as:
 The amount of total hardness in water is estimated via
complexometric titration. This is important in water
treatment for domestic and industrial purposes.
 It determines the concentration of metal ions in food
samples, which can be harmful to human health if present
in excess.
 It's commonly used in the pharmaceutical sector to
determine the amount of metal ions present in medicines
which affect their safety.

43.  Complexometric titration is used to determine the
concentration of metal ions in environmental samples that
has adverse effects on human health and the environment.
 Many cosmetic products contain titanium dioxide.
Complexometric titration can be used to examine this.
 It is employed in the examination of urine samples.
 It is used in biological samples such as blood and urine to
determine the concentration of metal ions, indicative of
certain diseases and disorders.
 In analytical chemistry, it is commonly used.

44.  Complexometric titration is a technique to determine the
concentration of metal ions in a sample.
 As volume measurements are important, complexometric
titration is also known as volumetric analysis.
 The volume of a titrant that has been reacted is known as
titrant volume.
 This technique involves the use of chelating agents to form
complexes with metal ions facilitating their detection.
 The choice of chelating agent depends on the metal ion being
analyzed, and suitable indicators are used to detect the
endpoint of the titration.
 This technique has a wide range of applications in various
fields, including water analysis, environmental analysis, and
pharmaceutical analysis.