Abstract:

Determination of the stoichiometric ratio and stability constants of iron(Ⅱ)-(1, 10-phenanthroline) complex via UV-Visible spectrophotometry is an important experiment in chemistry and related fields. Because laboratory conditions have been significant improved in recent times, the experimental procedure was optimized systematically in this study. The UV-Visible absorption spectra of the Fe(phen)₃²⁺ complex together with the free ligand were measured to determine the wavelength (λ) for the continuous variation methods. Meanwhile, frontier molecular orbital analysis of the complex provides clear visual evidence that the long-wavelength absorption band corresponds mainly to the metal-to-ligand charge transfer (MLCT) transition. Additionally, the experiments could achieve reliable and unbiased results for the composition and stability constants by analyzing experimental data using the Origin software. It is expected that these improvements and optimizations in the stoichiometric and stability constant determination experiments could help students become acquainted with the scientific experimental method, which is a critical requisite for student learning and development.

Key words: UV-Vis spectrophotometer, Tris(1, 10-phenanthroline)iron(Ⅱ), Method of continuous variation, Stoichiometric ratio of complex, Stability constant