Thursday, December 30, 2021

Assay of calcium carbonate

Learn about the assay of calcium carbonate through a laboratory experiment or practical.

Aim:

To determine the percentage purity of calcium carbonate using standard 0.1 N EDTA (Direct titration).

Reference: Indian Pharmacopeia (IP)

Requirements:

Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.

Chemicals: Calcium carbonate (CaCO3), hydrochloric acid (HCl), disodium edetate (EDTA), and calcon indicator mixture, etc.
Preparation of dilute hydrochloric acid:

Preparation of 0.05 M EDTA solution:

Click here to get the procedure.

Preparation of sodium hydroxide solution:

Take properly weighed 10.00 gm of oxalic acid and dissolve in 50 ml of distilled water in a volumetric flask, and properly mix it. Once it has completely dissolved, make up the volume to 100 ml.

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 properly weighed 01.00 gm of calcium carbonate and dissolved in 10.00 ml water and 03.00 ml dilute hydrochloric acid.
  • Boil for 10 minutes, then cool and dilute with water to 50.00 ml.
  • Titrate with 0.05 M EDTA to within a few ml of the predicted end-point, then add 08.00 ml of NaOH solution and 100 mg of calcon mixture as an indicator, and keep titrating until the color of the solution changes from pink to a blue.
  • To get accurate results, repeat the titration three times.
  • Properly record the readings of the burette.
  • Take their mean and calculate the % purity of calcium carbonate.

Observation table:

Sr. No.

Content in conical flask

Burette reading

Volume of titrant used (ml)

Initial

Final

1

 

 

 

 

2

 

 

 

3

 

 

 

 

Mean:

Calculation:

Each ml of 0.05M EDTA is equivalent to 0.005004 g of calcium carbonate.

% Assay = V x M x F / 0.05 x W x 100 / (100-LOD)

Where,
V is blank reading- sample reading
M is the molarity of 0.05M disodium Edetate
F is factor
W is the sample weight

Result:

The percentage purity of the calcium carbonate (CaCO3) sample was found to be_____.


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