Estimation of Magnesium Sulfate by Complexometric Titration

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

1. Burette

2. Erlenmeyer flask

3. pH meter or pH indicator

4. Magnesium sulfate solution (sample)

5. Standard EDTA solution

6. Buffer solution (pH ~10)

7. 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.