ANALYTICAL cHEMISTRY - V

Experiment 6

Principle

• Calcium is a mineral that is an essential part of bones and teeth. The heart, nerves and blood clotting systems also need calcium to work. Calcium is commonly taken by mouth for treatment and prevention of low calcium levels and resulting bone conditions including muscle cramps, weak bones due to low bone density, etc.

• Calcium rich foods include milk and dairy products, broccoli, calcium enriched citrus juices, etc.

• Side effects: Very high dose of calcium can cause kidney stones. Research has found an increased risk of heart attacks and strokes in people taking calcium supplements in addition to a diet high in calcium.

• Dosage: For a 19-50 years old individual the prescribed dosage is 1000 mg/day.

Complexometric titration of calcium with EDTA:

• When calcium ions are titrated with EDTA a relatively stable calcium complex is formed. When indicator is added to a solution containing calcium ions, the calcium - indicator complex is formed. Up on titration with EDTA, the indicator bound calcium ions form calcium - EDTA complex in 1:1 ratio. The indicator is set free and this determines the end point of the titration.

Apparatus required

Filter paper, Conical flask, Beaker, Pipette, Burette, Funnel, Mortar-Pestle, etc.

Chemicals required

Calcium tablet (500 mg), Concentrated HCl, 0.125 N EDTA solution, Eriochrome Black T (as indicator), Buffer pH 10, etc.

Preparation of reagents

1. 0.125 M EDTA solution:

1000 mL 1 M EDTA ≡ 372.24 g

500 mL 0.125 M EDTA ≡ 23.265 g.

2. Buffer pH 10:

Dissolve 17.5 gm NH₄Cl in water and add 142 mL liquor ammonia and dilute it with water in a 250 mL volumetric flask.

Result

1. Amount of calcium in tablet = ___________ mg.

2. % Error = _________ %.

Reference Material

1. G H Jeffery, J Bassett, J Mendham and R C Denney, Vogel's Textbook of Quantitative Chemical Analysis, 5th Edition

2. S. Suzanne Nielsen, Food analysis, 4th Edition

Questions