Estimation of Calcium Gluconate by Complexometric Titration

Introduction

• In pharmaceutical analysis, calcium gluconate (Ca(C₆H₁₁O₇)₂) is estimated using complexometric titration with EDTA as the titrant.

• The titration is based on the formation of a stable complex between EDTA and calcium ions (Ca²⁺).

Apparatus and reagents

1. Burette

2. Erlenmeyer flask

3. pH meter or pH indicator

4. Calcium gluconate 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 calcium gluconate (Ca(C6H11O7)2).

• Dissolve the sample 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 calcium gluconate sample to maintain a pH of ~10.

4) Add Indicator (optional)

• If using Eriochrome Black T, add a few drops. The solution will turn pink due to the presence of calcium ions.

5) Titration

• Titrate the calcium gluconate solution with the EDTA solution from the burette.

• As EDTA forms a complex with Ca²⁺, the solution's color will persist (pink if using Eriochrome Black T) until all calcium ions are complexed.

6) Endpoint Detection

• The endpoint is reached when the color of the solution changes, typically from pink to blue (if using Eriochrome Black T) or from a noticeable change in the solution color.

• Note the volume of EDTA solution required to reach the endpoint.

7) Calculations

• Amount of Ca(C₆H₁₁O₇)₂ (in grams):

  Amount (in grams) of Ca(C6H11O7)2 = (Volume of EDTA × Molarity of EDTA × Molar mass of Ca(C6H11O7)2) / 2

• The factor of 2 accounts for the stoichiometry, as each Ca²⁺ ion reacts with one mole of EDTA.