Estimation of Calcium Gluconate by Complexometric Titration

Objective:

To estimate the amount of calcium gluconate in a given sample using complexometric titration with EDTA as the titrant.

Principle:

In this titration, calcium ions (Ca2+) react with EDTA (ethylenediaminetetraacetic acid) to form a stable 1:1 complex. The endpoint is detected using an indicator, usually Murexide or Eriochrome Black T, which changes color when all calcium ions have reacted with EDTA.

Requirements:

Reagents:

• Standard EDTA solution (0.01 M or appropriate concentration).
• Murexide indicator (or Eriochrome Black T).
• Buffer solution (pH 10): Ammonium chloride-ammonia buffer.
• Calcium gluconate solution (unknown concentration).
• Distilled water.

Apparatus:

• Burette.
• Pipette.
• Conical flask.
• Beaker.
• Measuring cylinder.

Procedure:

1. Preparation of Reagents

EDTA Solution: Prepare a 0.01 M EDTA solution by dissolving 3.7224 g of disodium EDTA in 1 L of distilled water.
Buffer Solution (pH 10): Prepare by mixing ammonium chloride and ammonia in a 1:1 ratio and adjusting the pH to 10 using dilute ammonia.
Indicator Solution:
– Murexide is prepared by dissolving 0.2 g in 100 mL of distilled water.
– For Eriochrome Black T, prepared by dissolving 0.5 g in 100 mL of ethanol or water.

2. Preparation of Calcium Gluconate Solution

• Accurately weigh a known amount of calcium gluconate sample (e.g., 1 g).
• Dissolve the sample in a small volume of distilled water.
• Transfer to a 250 mL volumetric flask and dilute to the mark with distilled water.

3. Titration

• Pipette 25 mL of the calcium gluconate solution into a clean conical flask.
• Add 5 mL of buffer solution (pH 10) to maintain the required pH for the reaction.
• Add a pinch of Murexide indicator (or 3-4 drops of Eriochrome Black T).
  – If using Murexide, the solution turns pink.
  – If using Eriochrome Black T, the solution turns wine-red.
• Fill the burette with the standard EDTA solution.
• Titrate the solution with EDTA while swirling the conical flask until the color changes:
  – For Murexide, the color changes from pink to purple.
  – For Eriochrome Black T, 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

Example Calculation:

Results:

The amount of calcium gluconate in the sample is 0.0646 g per 25 mL of solution.