Abstract: “The electronic configuration and chemistry of iron allows for a variety of coordination compounds and complexes to be formed. These complexes consist of the metal ion bound to ligands, which can be nonmetal ions, small molecules such as H2O, NH3, or large molecules including organic ligands. Metal complexes are important to the function of proteins. For example, heme is a coordination complex of an iron ion coordinated to a porphyrin. Heme is a precursor to hemoglobin which can bind oxygen in the blood. Another example is nitrogenase, an enzyme in cyanobacteria that is important in nitrogen fixation. We are developing an inorganic chemistry lab experiment that introduces students to the coordination chemistry of iron by allowing them to relate complex formation to color changes and solubility. The objectives of the experiments presented here are: i) Observe and understand the chemistry of transition metal complexes. ii) Correctly calculate and prepare solutions of known concentrations. iii) Determine and explain changes in color and solubility in terms of metal-ligand interactions. iv) Analyze metal-ligand formation and generate evidence-supported conclusions. Students explore several concepts related to transition metal chemistry, coordination chemistry, oxidation-reduction reactions, and solubility.”
Great presentation! What age group is this experiment designed for? Is this being developed for a freshman level undergraduate chemistry course?
Thank you! This lab is designed for a third-year inorganic chemistry lab, but it could easily be modified to fit a general chemistry curriculum.
Very nice presentation and a very well designed lab experiment.
Have you thought about adding a more quantitative way to measure solubility (Maybe with AA)? As determining if there is a precipitate might be difficult in the brightly colored solutions.
As previously mentioned the pH will be shifting throughout the lab, have you considered directly demonstrating the effect of pH after a single step? For example, having the students take an aliquot of step 4, and adding acid or base and observing the color change.
Thank you for these suggestions! We will certainly take them into account as we develop the experiment further. As the course transitions to more in-person instruction, it may be helpful to split a class into multiple groups. This would allow each group to focus on measuring a different value such as solubility, pH, or absorbance as the experiment progresses.
Nice job and as previous person commented very clear. Also from a pedagogical standpoint, isn’t the oxidation state of the Fe changing in some of these reactions, and does that have an effect on the observed color? As a second question, isn’t the pH changing over the series, and does this have an effect?
Thank you for your questions! Yes, both the pH and the oxidation state of iron change throughout the experiment. These factors will affect the structure of the complex formed, which affects the color seen. Students are given online resources that help them explore the effect of these factors in the experiment.
Well done presentation. The poster was easy to read and the use of techniques to highlight portions of the poster during the presentation was effective (circling sections, expanding figures).
From a pedagogical standpoint, I have two operational questions
1) How long would this lab take an average student both in lab (if you were to do it face-to-face) and in a virtual environment
2) You list pre-lab questions. Have you developed any post-lab questions or application questions based on the observations the student make during the lab. Exploring the concepts of coordination number and geometry might be a useful extension for this lab for each of the structures synthesized
Thank you for your interest in my project! This lab is estimated to take 3 hours, both in person and online. The online lab requires students to complete all the same steps, with the only change being that they watch a video rather than running the reactions themselves. After performing the experiment, students are asked to come up with possible chemical equations and complex structures for certain steps in the experiment. Asking students to predict the complex structure based on the colors observed would definitely encourage deeper thought if added to the post-lab questions.