Estimation of Magnesium Sulfate by Complexometric Titration

Objective:

To estimate the amount of magnesium sulfate (MgSO₄) in a given sample using complexometric titration with EDTA as the titrant.

Principle:

In this titration, magnesium ions (Mg²⁺) react with EDTA (ethylenediaminetetraacetic acid) to form a stable 1:1 complex. The endpoint is detected using an indicator, typically Eriochrome Black T, which changes color when all the magnesium ions have reacted with EDTA.

Requirements:

Reagents:

1. Standard EDTA solution (0.01 M or appropriate concentration).
2. Eriochrome Black T indicator solution.
3. Buffer solution (pH 10): Ammonium chloride-ammonia buffer.
4. Magnesium sulfate solution (unknown concentration).
5. Distilled water.

Apparatus:

1. Burette.
2. Pipette.
3. Conical flask.
4. Beaker.
5. Measuring cylinder.

Procedure:

1. Preparation of Reagents

• EDTA Solution: Dissolve a calculated amount of disodium EDTA in distilled water and dilute to a known volume (e.g., 0.01 M solution).
• The molar mass of disodium EDTA=372.24 g/mol
• Weigh and dissolve 3.7224 g of EDTA in 1L of water for a 0.01 M solution.
• Buffer Solution (pH 10): Mix ammonium chloride and ammonia in a 1:1 ratio. Add sufficient ammonia to maintain pH 10.
• Indicator Solution: Dissolve 0.5 g of Eriochrome Black T in 100 mL of ethanol or water.

2. Preparation of Sample Solution

• Accurately weigh a known amount of magnesium sulfate (MgSO₄) or its sample.
• Dissolve the sample in distilled water and dilute to a known volume (e.g., 250 mL) in a volumetric flask.

3. Titration

• Pipette 25 mL of the magnesium sulfate solution into a clean conical flask.
• Add 5 mL of buffer solution (pH 10) to maintain the required pH for the reaction.
• Add 3-4 drops of Eriochrome Black T indicator. The solution turns wine-red in the presence of magnesium ions.
• Fill the burette with the standard EDTA solution.
• Titrate the solution while swirling the conical flask until the color changes from wine-red to blue. Note the burette reading at the endpoint.

4. Repeat Titration

• Repeat the titration 2-3 times for concordant readings.
• Record the readings and calculate the average volume of EDTA used.

Calculation

Reaction Equation:

1 mole of Mg²⁺ reacts with 1 mole of EDTA.

The calculation formula:

Example Calculation:

Result:

The amount of magnesium sulfate in the sample is 0.0241 g0.0241\ g0.0241 g per 25 mL of solution.