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Determine concentration of calcium ions

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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