Tuesday, August 24, 2021

Preparation and standardization of 0.05 M EDTA solution

Learn about the preparation and standardization of 0.05 M EDTA solution through a laboratory experiment or practical.

Aim:

To prepare and standardize 0.05 M EDTA solution using calcium chloride.

Requirements:

Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: LR grade disodium edetate (EDTA), ammonia (NH3), calcium chloride (CaCl2), ammonium chloride (NH4Cl), hydrochloric acid (HCL), and solochrome black-T indicator, etc.
Apparatus: Digital/analytical balance, and Ultrasonicator.

Principle:

The standardization of EDTA solutions is based on complexometric titration. When the indicator is introduced to a calcium chloride solution, the Ca-indicator complex forms. When titrating against disodium edetate, the complex converts calcium to EDTA, releasing a blue-colored indicator, indicating the reaction's endpoint.
The following is the reaction that is involved in this titration.

Preparation and standardization of EDTA solution

The molecular weight of disodium edetate (EDTA)is 336.21 g/mol.

Preparation of 0.05 M EDTA solution:

Take 18.16 gm of EDTA and dissolve in 300 ml of distilled water in a volumetric flask, and properly mixing it. Once it has completely dissolved, make up the volume to 1000 ml.

Preparation of 0.05 M calcium chloride:

Take 07.35 gm of CaCl2 and dissolve in 500 ml of distilled water in a volumetric flask, and properly mixing it. Once it has completely dissolved, make up the volume to 1000 ml.

Preparation of 1 M ammonia solution:

Take 75.00 ml of ammonia (Strong) using a pipette, dilute in 100 ml of distilled water in a volumetric flask, and properly mixing it.

Preparation of ammonia buffer of 10 pH:

Take 05.40 gm of NH4Cl, and 35.00 ml of 10 M ammonia solution and dissolve in 100 ml of distilled water in a volumetric flask and properly mixing it.

Titration procedure:

  • All glassware should be cleaned and dried according to standard laboratory procedures.
  • Before filling the burette for the titration, rinse it with distilled water and then pre-rinse it with a portion of the titrant solution. Pre-rinsing is required to make sure that all solution in the burette is the desired solution, not a contaminated or diluted solution.
  • Take the unknown stock solution of titrant in a clean and dry beaker then fill the burette using the funnel.
  • Remove air bubbles from the burette and adjust the reading to zero.
  • Take 10.00 ml of calcium chloride solution and pour it into a conical flask.
  • To make it alkaline, add 05 mL of buffer solution previously adjusted to pH 10.
  • Add 2 drops of solochrome black-T indicator.
  • Titrate the sample solution with EDTA until the endpoint is reached. The actual endpoint is indicated by a change in the color of the solution.
  • Properly record the readings of the burette.
  • To get accurate results, repeat the titration three times.
  • Take their mean and calculate the molarity of EDTA.

Observation table:

Sr. No.

Content in conical flask

Burette reading

Volume of titrant used (ml)

Initial

Final

1

 

 

 

 

2

 

 

 

3

 

 

 

 

Mean:


Calculations:

M1V1= M2V2
M2 = V1 M1 / V2

Where,
M1 is molarity of calcium chloride
V1 is volume of calcium chloride
M2 is molarity of disodium edetatesolution.
V2 is volume of disodium edetate solution used

Result:

The strength of the prepared EDTA solution was found to be_____M.


Commonly asked questions on titration of EDTA are as follows.

Why buffer solution is used in EDTA titration?
In EDTA titration, a buffer of ammonium chloride (pH 10) is used as it resists pH change. This is since all reactions involving metal ions and EDTA are pH-dependent.

Why do we standardize the EDTA solution?
Standardization of a prepared EDTA solution is performed to determine its exact molarity.

Which indicator is used in standardizing EDTA?
Eriochrome Black T indicator is used in the complexometric EDTA titration which produces color change from blue to pink.

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