Experiment
Determine the concentration of calcium ions by complexometric titration
Introduction:
Complexometric titration is a type of titration in which an undissociated complex is formed. This method is used to determine the hardness of water, the calcium content in milk, and the amount of calcium carbonate in various solid materials.
In this method, EDTA (ethylenediaminetetraacetic acid) forms a complex with a metal ion. Patton Reeder's indicator is used in this method which is a blue dye. Dye-Metal ion is less stable than the Metal-EDTA complex. That's why when EDTA is added to the Dye-Metal complex it forms the Metal-EDTA complex for the stable association. The change in colour from pink/red to blue indicates the endpoint of the titration.
Reaction:
\[Ca-PR\; + \; EDTA^{-4} \; \rightarrow PR \; + \; [Ca-EDTA]^{-2}\]
PR | Blue colour
Ca-PR | Pink/red colour
Equipments:
- 10 mL and 20mL pipette
- 250 mL conical flask
- 100,250 and 500mL volumetric flask
- pH indicator paper
- Burette and stand
- 10 mL and 100mL measuring cylinder
Procedure:
- Take a calcium ion sample that is eggshell of about 0.5 g in a small beaker or conical flask.
- Add dilute 20mL of dilute HCl and wait till the eggshell dissolve.
- Neutralize the solution with dilute NaOH till the pH is almost 7.
- Transfer the solution to a 100mL volumetric flask and add distilled water up to the mark.
- Pipette out liquid from the sample about 10mL into an Erlenmeyer flask and add about 40mL of distilled water and 4mL of 8M NaOH and swirl the solution for 5 minutes.
- Add 0.1g of Patton Reeder's indicator into the Erlenmeyer flask.
- Titrate the sample with EDTA solution.
- An endpoint will achieve when colour changes from red/pink 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 |
Result:
Mass of calcium ions = _____________