Complexometric Titration Experiment
Determining Calcium Ion Concentration
Introduction
Complexometric titration is a method used to determine the concentration of metal ions like calcium in various substances. This method uses a chelating agent, EDTA, to form a complex with the metal ions. The endpoint of the titration is determined using Patton Reeder's indicator, which changes color from pink/red to blue.
Reaction
The reaction between calcium ions and EDTA is as follows:
\[Ca^{+2} + H_{2}EDTA^{-2} \rightarrow PR + [Ca-EDTA]^{-2} + 2H^{+}\]
PR | Blue color
Ca-PR | Pink/red color
Equipments
- 10 mL and 20 mL pipette
- 250 mL conical flask
- 100, 250, and 500 mL volumetric flasks
- pH indicator paper
- Burette and stand
- 10 mL and 100 mL measuring cylinders
Procedure
- Take a calcium ion sample (eggshell) of about 0.5g in a small beaker or conical flask.
- Add 20mL of dilute HCl and wait until the eggshell dissolves.
- Neutralize the solution with dilute NaOH until the pH is almost 7.
- Transfer the solution to a 100mL volumetric flask and add distilled water up to the mark.
- Pipette out 10mL of the liquid into an Erlenmeyer flask and add 40mL of distilled water and 4mL of 8M NaOH. Swirl for 5 minutes.
- Add 0.1g of Patton Reeder's indicator to the flask.
- Titrate the sample with EDTA solution.
- The endpoint is achieved when the color changes from pink/red to blue.
- Repeat the process until concordant readings are obtained.
Observations and Calculations
| Sr # | Initial Volume (Vi) | Final Volume (Vf) | Volume (Vf - Vi) |
|---|---|---|---|
| 1 | ______ | ______ | ______ |
| 2 | ______ | ______ | ______ |
| 3 | ______ | ______ | ______ |
Average volume of EDTA = ________
Moles of EDTA = Molarity of EDTA × Average volume
Moles of calcium ions = Moles of EDTA
Molarity of calcium ions = moles / Volume = ________
Mass of calcium ions = moles of calcium ions × Molar mass of calcium = ________
Result
Mass of calcium ions = _____________
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