Introduction:
In pharmaceutical analysis, the estimation of magnesium sulfate (MgSO₄) is done using complexometric titration with EDTA as the titrant. This method relies on the formation of a stable complex between EDTA and magnesium ions (Mg²⁺).
Apparatus and reagents:
Burette
Erlenmeyer flask
pH meter or pH indicator
Magnesium sulfate solution (sample)
Standard EDTA solution
Buffer solution (pH ~10)
Eriochrome Black T indicator (optional)
Procedure:
1. Preparation of Sample:
Weigh a sample of magnesium sulfate, dissolve it 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 sample to maintain a pH of ~10.
4. Indicator (Eriochrome Black T):
If using Eriochrome Black T, add a few drops. The solution will turn pink due to the presence of magnesium ions.
5. Titration:
Titrate the magnesium sulfate solution with the EDTA solution from the burette.
As EDTA complexes with Mg²⁺, the solution's color (pink if using Eriochrome Black T) will remain until all magnesium ions are bound.
6. Endpoint Detection:
The endpoint is reached when the color changes, typically from pink to blue (if using Eriochrome Black T), or there is a noticeable color change.
7. Record Volume:
Note the volume of EDTA required to reach the endpoint.
Calculations:
Amount of MgSO₄ (in grams):
Amount (in grams) of MgSO4 = (Volume of EDTA × Molarity of EDTA × Molar mass of MgSO4) / 2
% MgSO₄:
% MgSO4 = (Volume of EDTA × Molarity of EDTA × Molecular weight of MgSO4 × 100) / (Volume of sample × Weight of sample)
The factor of 2 accounts for the reaction stoichiometry, as each Mg²⁺ ion reacts with one mole of EDTA.