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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