Investigation of Complexing Abilityedta

Introduction

Objectives

1. To examine the colour changes of Eriochrome Black T, an indicator commonly used in EDTA titration, upon complexation with magnesium ion 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 titration.

Methodology

Part 1

1. Three boiling tube was labeled as A,B and C and 5ml of the following solution was added 1M HCl, 1M NaOH and NH3/NH4Cl buffer solution at pH 10 in order.

2. Distilled water was added,10ml and 3 drops of Eriochrome Black T was added into each boiling tube . the colour changes was observed.

3. One mL of magnesium nitrate was added into each test tube from part 2 and once again the colour changes was observed.

Part 2

1. Na2EDTA was weighed about 0.9 g and put into volumetric flask.

2. The volumetric cell was filled up about 100mL of distilled water and was shaked until the solid dissolves.

3. Then, the distilled water was added into the solution until graduated mark and shaked to get the homogenous solution.

Part 3

1. Three conical flask was labeled and conical flask A was filled with 5 mL of Mg(No3),90 mL distilled water, 10 mL NH3/NH4Cl buffer solution at pH 10, 10 mL 0.01 M EDTA solution. Conical flas B was filled with 3 drops Etiochrome Black T, 90 mL distilled water, 10mL NH3/NH4Cl buffer solution at pH 10. Conical flask C was filled with 3 drops Etichrome Black T, 90 mL distilled water, 10mL NH3/NH4Cl buffer solution at pH 10, 5 mL Mg(No3)2 solution.

2. The colour chances was observed.

3. Then 10 mL of 0.01 MEDTA was added to conical flask B and C, the colour changes was observed once again.

Result

Part 1

A | B | C |

Initial colour | Final colour | Initial colour | Final colour | Initial colour | Final colour |

Wine red | Remain wine red | Dark red | Remain the same | Dark blue | purple |

Part 3

A | B | C |

Initial colour | Final colour |...