Complexometric Titration B.Pharm 1st Semester, Estimation of Calcium Gluconate, EDTA

This Presentation includes all the topics that are mentioned in the PCI syllabus for B.Pharm 1st Semester.

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Complexometric
Titration
Presented by- Mr. Debashis Mishra
Assistant Professor, IPT, Salipur
Odisha, India, Pin - 754202

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✓Complexometric titration: Classification
✓Metal ion indicators
✓Masking and demasking reagents
✓Estimation of Magnesium sulphate and
calcium gluconate.
Contents

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Introduction to
Complexometric Titration
❑Complexometric titration is a volumetric analytical technique that relies on
the formation of colored complexes between a metal ion and a complexing
agent.
❑Applications of complexometric titration are widespread, including
assessing water hardness, analyzing pharmaceutical products, and
monitoring environmental samples to ensure safety. Its precise and
selective nature makes it essential in both industrial and research contexts.
❑The most commonly used complexing agent is EDTA (Ethylene Diamine
Tetra Acetic Acid), which forms stable complexes with a variety of metal
ions. This method plays a vital role in accurately determining metal ion
concentrations in diverse solutions.

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Classification of Complexometric Titrations
i. Direct Titration
In this method, the analyte is titrated
directly with EDTA. It is straightforward and
typically used when the metal ion reacts
rapidly. For example, estimation of Bismuth
Nitrate, Calcium Gluconate, Magnesium
Sulphate, Zinc Oxide.
ii. Back Titration
Here, excess EDTA is added to the sample
and then titrated back with a standard
solution. This approach is useful when the
reaction is slow or the indicator is blocked,
such as in the determination of Aluminum
Hydroxide.
iv. Alkalimetric/Indirect Titration
iii. Displacement Titration
The Analyte displaces another metal like
Zn, Mg from its less stable complex. The
liberated ions are then titrated with edetate.
Mercury, Lead, Cadmium determination
uses this technique.
When a metal ion reacts with a complexing
agent, it forms a complex and releases a
proton (H⁺). The amount of acid (H⁺) released
is equivalent to the amount of metal ion
present. This H⁺ is then titrated with Std.
NaOH (alkali), and the volume of NaOH used
gives information about the metal ion
concentration.

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Metal Ion Indicators
Definition & Role
❑Metal ion indicators are chemical compounds that visibly change color when they bind
to metal ions. They are commonly used in complexometric titrations to determine the
concentration of metal ions in a solution.
❑They must exhibit strong binding, a sharp color change and selectivity for specific ions
to indicate the titration endpoint clearly.
Common Metal Ion Indicators
Indicator Metal Ions Detected pH Range Color Change (Endpoint)
Eriochrome Black T Ca²⁺, Mg²⁺ 8–10 Wine-red → Blue
Murexide Ca²⁺ ~11 Pink → Purple
Xylenol Orange Fe³⁺, Bi³⁺ 1–5 Yellow → Red
Calmagite Mg²⁺, Ca²⁺ 10 Red → Blue
1-(2-Pyridylazo)-2-
naphthol (PAN)
Zn²⁺, Cu²⁺ 5–9 Red → Yellow

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Masking and Demasking Reagents
Masking Agents
❑Masking agents are used to form complexes with the interfering metal ions. This
prevents the interfering metal ions from interfering with the determination of the metal
ion of interest/analyte.
❑Examples include cyanide, fluoride and triethanolamine. This selective blocking helps to
mask ions like Fe³⁺ or Cu²⁺ in EDTA titrations.
Requirement:
❑During estimation of a specific ion, sometimes other ionic impurities may also get
estimated. This gives false values.
❑Also when two or more ions are to be estimated in a mixture, each ions has to be
selectively titrated.
Demasking Agents
❑Demasking agents are used to remove the masking agent from the interfering metal
ions, allowing the metal ions to be titrated again if necessary. Demasking agents
typically form a more stable complex with the masking agent than the metal ion.
❑Examples include Sodium Cyanide, Formaldehyde and Potassium Iodide which are
used to demask Copper, Aluminum and Mercury respectively.

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Estimation of Calcium Gluconate
2. Titration Process
1. Principle
❑The complexing agent EDTA is an electron donating molecule which forms one or more
covalent bonds with metallic ions to produce a complex.
❑A metal ion sensitive indicator is used to detect the end-point. The indicator forms loose
complexes with metal ion and shows a different colour during the titrations. It gives original
colour at the end-point due to the liberation of free dye from the metal-dye complex.
❑In the estimation of calcium gluconate, the sample solution is titrated with M/20 or 0.05M
EDTA solution using pH 10 buffer solutions.
❑The volume of EDTA consumed depends upon the calcium gluconate present in the sample.
Standardization of EDTA solution: Pipette out 10 ml of 0.05M CaCl
2 solution into a conical flask
and 5 ml of pH 10 buffer solution. Add 2 or 3 drops of Solochrome/Erichrome Black T indicator
and titrate against EDTA solution until the wine red turns blue. Repeat the titration for concordant
values.
❑Calculate the molarity of EDTA from the following formula:
V
1M
1 = V
2M
2
∴ M
2=
M
1V
1
V
2
Where, V
1 = Volume of 0.05 CaCl
2 solution = 10 ml
M
1 = Molarity of CaCl
2 solution = 0.05M
V
2 = Volume of EDTA rundown (Average burette reading)
M
2 = Molarity of EDTA Solution =?

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❑Weigh accurately 0.2 g of calcium gluconate and dissolve in 50 ml of warm water.
Add 5 ml of M/20 MgSO
4 solution, 10ml of pH 10 buffer solution.
❑Titrate the contents of the flask against standard EDTA using SBT indicator. Perform
a blank titration also and subtract this value from sample titration. Repeat the
titration for concordant values.
3. Sample Preparation & Assay Procedure
4. Result Calculation
Equivalent or I.P. Factor: Each ml of 0.05M EDTA ≡ 0.0215 gm of Calcium gluconate
The Percent purity of
Calcium gluconate =
Vol. of EDTA × I.P.factor × 100 × M of EDTA (Actual)
Wt. of Calcium gluconate in grams × M of EDTA (Expected)

❑Then calculate the concentration of calcium gluconate based on the volume of
EDTA consumed.

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Estimation of Magnesium Sulfate
1. Principle
❑Magnesium ions (Mg²⁺) react with EDTA (ethylenediaminetetraacetic acid) in a 1:1 ratio to
form a stable complex. At pH 10, Eriochrome Black T forms a wine-red complex with Mg²⁺.
❑As EDTA is added, it binds with Mg²⁺, releasing the indicator, which changes color to blue
at the endpoint.
2. Procedure
Standardization of EDTA solution- Follow the same procedure as given earlier by using
0.01M CaCl
2 solution.
Assay Procedure
❑Pipette 25.0 mL of MgSO₄ solution into a conical flask. Add 5 mL of buffer solution (pH
10). Add 2–3 drops of Eriochrome Black T; the solution turns wine-red.
❑Titrate with 0.01 M EDTA from a burette until the color changes from wine-red to clear
blue.
❑Record the volume of EDTA used. Repeat the titration to get concordant readings.
The Percent purity of
MgSO4
=
Vol. of EDTA × I.P.factor × 100 × M of EDTAActual
Wt. of MgSO4 in grams × M of EDTAExpected

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Applications and Significance
Water Hardness Testing
Quantifies total calcium and magnesium levels,
crucial for assessing water quality and industrial
process control.
Pharmaceutical Quality Control
Ensures accurate dosage and safety by analyzing
metal ion content in medications.
Environmental Monitoring
Detects and measures heavy metal pollutants in
air, soil, and water to safeguard ecosystems.
Clinical Chemistry and Industry
Used in electrolyte analysis in biological samples
and managing metal ion concentrations in
manufacturing baths.

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Conclusion
Versatility
Complexometric titration is a powerful technique for analyzing
various metal ions across many fields.
EDTA Importance
EDTA remains the preferred complexing agent due to its
efficiency and stability in forming metal complexes.
Indicators and Reagents
Selection of proper metal ion indicators and masking/demasking
reagents is essential for accurate endpoint detection and
selectivity.
Accurate Determinations
This method ensures precise quantification of metal ions,
supporting quality control, research, and environmental safety.