EDTA Titration

CHEM 1212L

Formal Laboratory Report

I. Introduction: 

The purpose of this experiment was to acquire a more advanced understanding, through active participation, of the process of titration as it is used in the laboratory and its application outside the lab. Percent composition of Mg2+ ions in a measured sample of a magnesium salt was to be determined as a result of this experiment. Specifically, the type of titration executed was complexometric titration of a magnesium salt solution using EDTA (C10H16N2O8). This method involves a volumetric analysis resulting in the formation of a colored complex, indicating the end point of titration. In some experiments, the colored complex can be formed using the organic dye indicator, Eriochrome Black T (C20H12N3O7SNa). This experiment deviated from the lab manual slightly by using calmagite, which makes the color change more visible in the reaction. Concentration of the Mg2+ in the solution can be determined through the calculation of the concentration because the molar ratio is 1:1. Concentration in this experiment was determined visually through titration with an indicator, calmagite, that turns light blue when the reaction between the two liquids was complete, a point which was subject to judgment of the student. Initially, the dye was wine red with a pH of 9.3. When the EDTA was added, a color change was observed. The color change indicated that all the dye had been displaced from the metal cations in the solution and had formed a chelate. A chelate is the complex formed through the process of reversible bonding of a ligand to a metal ion. In this experiment, the ligand was EDTA (ethylenediamine tetraacetic acid). These complexes are stable in a buffer solution. Carrying out the reaction in a buffer solution removes H+ as it is formed, favoring the formation of the cation-EDTA complex so it was assumed that the reaction goes to completion. EDTA has four carboxyl groups and two amine groups, giving it many lone pairs to donate as a Lewis base. Two different equations were used in determining molar concentration, or molarity. The reaction appears as follows:

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Mg2+(aq)  Mg2+(aq)+ calmagite  Mg-calmagite + Mg2+(excess)                                 Mg-calmagite + Mg2+(excess) + EDTA4-  Mg-EDTA2- + calmagite

Pre-Lab Question:

1.        A buffered solution containing lead ions, Pb2+, was titrated to the end point using 37.53mL of 0.10M EDTA. What is the mass of lead ions in solution?

Moles EDTA: (0.03753L)x(0.10M)=0.003753 mol Pb2+

Mass Pb2+: (0.003753 mol)x(207.2 g/mol)=0.778g

II. Procedure: 

        Only plastic laboratory equipment was used for this experiment as opposed to glass to avoid a chemical reaction destroying the glass. The student obtained a bottle of ~0.01M EDTA solution, a bottle of indicator, and a sample of ...

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