Edta Analysis

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General Chemistry

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Investigation of the complexing ability of ethylene diamine tetra-acetic acid (EDTA) |

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Name: CHENG HUEI SZE

Student ID: BP0913034308

Group: F

Objective

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 titration.

Introduction

Ethylenediaminetetraacetic acid (EDTA) is a compound with 2 tertiary amino groups and 4 carboxyl groups which is widely used as a titrating agent in complexometric titration. EDTA has six complexing groups because there is a lone pair of electrons found on each of the two nitrogen atoms and each of the four carboxyl groups. The structure of EDTA can be shown as following:

The formation of metal ion-EDTA complexes depends on the pH. In EDTA titrations with the use of Eriochrome Black T as an indicator, the solution must be buffered with pH 10, so the metal ions-EDTA complex formation will be preferred as the H+ ions formed upon the ionization of EDTA will be neutralized by the hydroxide ions and the equilibrium position will shift towards the right hand side, favouring the forward reaction. Besides, highly basic condition favours the formation of Y4- form of EDTA, which is the most desirable state.

The reaction of EDTA titration can be expressed in the following equation:

M2+ + H4Y MH2Y + 2H+

Eriochrome Black T is a specific indicator that is commonly used in EDTA titration. It can be represented by the formula H3In as it contains three ionisable protons. In neutral or basic solutions, it forms a doubly...