Edta

Objectives:

1. To examine the colour changes of Eriochrome Black T, an indicator commonly used in EDTA titration, upon complexation with magnesium ions at various pH conditions.

2. To investigate the complexing ability of EDTA.

3. To determine the concentration of magnesium ions in a solution using EDTA.

Materials:

Chemicals

Na2EDTA.2H2O (FW = 372.24), ammonia/ammonium chloride buffer solution at

pH 10, 1 M hydrochloric acid, 1 M sodium hydroxide, Eriochrome Black T,

magnesium nitrate solution.

Apparatus

250 mL volumetric flask, droppers, 20 mL test tubes, 100 mL beakers, 250 mL

conical flasks, 50 mL burettes, 25 mL pipettes, pipette fillers, funnels.

Procedure:

Part 1: Colour changes of Eriochrome Black T upon complexation with magnesium ions

in HCl solution, NaOH solution and NH3/NH4Cl buffer at pH 10.

1. Three test tubes were labelled A, B, and C and 5 mL of 1 M HCl, 1 M NaOH, and NH3/NH4Cl buffer solution at pH 10 were added into the test tube respectively.

2. 10 mL of distilled water and 3 drops of Eriochrome Black T was added into each tube and the colour change of the solution in the test tube was observed and recorded.

3. 1 mL of magnesium nitrate solution was added into each test tube from Step 2 and the colour change of the solution in the test tube was observed and recorded.

Part 2: Preparation of 0.01 M EDTA solution

1. 0.9 g of Na2EDTA.2H2O was accurately weighed into a 250 mL volumetric flask.

2. The volumetric flask was filled up with about 100 mL of distilled water and shaken until all the solids dissolved.

3. The solution was then toped up to the graduated mark with distilled water and shaken to obtain a homogenous solution.

Part 3: Abstraction of magnesium ions from magnesium-eriochrome black T complex using EDTA.

1. Three conical flasks were labelled A, B, C and following solutions were added into the flasks respectively:

Flask A: 5 mL Mg(NO3)2 solution, 90 mL...