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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 of Magnesium Sulfate
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.
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