Introduction:
In pharmaceutical analysis, calcium gluconate (Ca(C₆H₁₁O₇)₂) is estimated using complexometric titration with EDTA as the titrant.
The titration is based on the formation of a stable complex between EDTA and calcium ions (Ca²⁺).
Apparatus and reagents:
Burette
Erlenmeyer flask
pH meter or pH indicator
Calcium gluconate solution (sample)
Standard EDTA solution
Buffer solution (pH ~10)
Eriochrome Black T indicator (optional)
Procedure:
1) Preparation of Sample:
Weigh a sample of calcium gluconate (Ca(C6H11O7)2).
Dissolve the sample in distilled water and transfer it to an Erlenmeyer flask.
2) Preparation of the Titrant (EDTA):
Use a standard EDTA solution, typically 0.01 M.
3) Buffering the Solution:
Add a buffer solution to the calcium gluconate sample to maintain a pH of ~10.
4) Add Indicator (optional):
If using Eriochrome Black T, add a few drops. The solution will turn pink due to the presence of calcium ions.
5) Titration:
Titrate the calcium gluconate solution with the EDTA solution from the burette.
As EDTA forms a complex with Ca²⁺, the solution's color will persist (pink if using Eriochrome Black T) until all calcium ions are complexed.
6) Endpoint Detection:
The endpoint is reached when the color of the solution changes, typically from pink to blue (if using Eriochrome Black T) or from a noticeable change in the solution color.
Note the volume of EDTA solution required to reach the endpoint.
7) Calculations:
Amount of Ca(C₆H₁₁O₇)₂ (in grams):
Amount (in grams) of Ca(C6H11O7)2 = (Volume of EDTA × Molarity of EDTA × Molar mass of Ca(C6H11O7)2) / 2
The factor of 2 accounts for the stoichiometry, as each Ca²⁺ ion reacts with one mole of EDTA.