Post Lab #5.docx - Post Lab#5 The Determination of...

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Post Lab #5: The Determination of Magnesium by Direct Titration with EDTA Introduction: The purpose of this week’s lab was to perform a titration on a complexation reaction. A complexation reaction is also known as a Lewis acid-base reaction (University of Michigan, 2016). Lewis acids, metal ions, and bases, ligands, were used in this experiment’s complexation reaction. The metal atoms, the acids, can bind with six ligands, bases, at once, sometimes at many different sites. These are multidentate ligands that have higher stability, where pH, ionic strength and metal-ion coordination are all factors in determining the stability (Uchimiya, 2014) An increase in molecules that are converted, means an increase in the entropy of the system, which makes the reaction more spontaneous. Since the reaction increased favorably, this was an example of the “chelate effect”. The chelate effect occurs when the water surrounded by the central metal ion is replaced using multidentate ligands, like EDTA (Clark, 2003).EDTA is a hexaprotic acid that ranges from H 2 Y 2+ to Y -4 . In this week’s experiment, the pH was 10, allowing the EDTA to be in its chelate form, completing the reaction. The end point was found by metal ion indicators, Eriochrome Black T, that formed complexes with metals. Once EDTA was added to the mixture, it reacted with the free Mg 2+ , then the MgIn complex. The anion of EDTA reacted with all polyvalent metal cations in a 1:1 solution. The change from red to blue indicated the endpoint of the titration. Procedure and Materials: 1. Dried MgO 2. 0.5% Eriochrome Black T indicator 3. Dried EDTA 4. Conc. NH 3 5. NH 4 Cl 6. Desiccator 7. 1 L volumetric flask 8. Analytical balance 9. Funnel 10. DI water 11. 250 mL beaker 12. Buret 13. 250 mL Erlenmeyer flasks
Qualitative Observations: In this week’s experiment, there were important qualitative observations that indicated the completion of the titrations performed. The solution that was titrated was colorless until the 0.5% Eriochrome Black T indicator was added, which turned the solution a very dark red. The solution that was in the buret was also colorless. Upon adding the titrant to the solution in the flask, the color changed from dark red to purple, then to blue. We were to stop titrating once the

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