This lab handout and supplementary materials were developed based on a publication in the Journal of Chemical Education:
Berger, P.; Adelman, N.; Beckman, K.; Campbell, D.; Ellis, A.; Lisensky, G. Preparation and Properties of an Aqueous Ferrofluid. J. Chem. Educ. 1999, 76 (7), 943-48
Students synthesize an aqueous ferrofluid in the magnetite (spinel) structure by mixing solutions of Fe(III) and Fe(II) with ammonia. The magnetite nanoparticles are then coated with surfactant to prevent agglomeration, and students can observe spiking in their ferrofluid. This experiment is a fun way to start out the semester, as it doesn't require a lot of previous knowledge and students get very excited about watching their ferrofluids "dance" with the magnets. It also serves as a memorable example of magnetic properties that can be attributed to unpaired electron spins in a crystal structure, which leads nicely into a materials science component of an inorganic course.
Practice wet lab skills, including: use of volumetric pipet, buret, vacuum trap apparatus, handling of acids and bases
Gain hands-on experience synthesizing magnetic nanoparticles
Play with a memorable example of magnetic properties determined by unpaired electrons and crystal structure
See prep instructions for a full list of all chemicals and equipment required (quantities calculated for a 12-student lab, working individually).
See instructor notes document.
We had 4 hours for this lab experiment, but most students were done early. Could probably be done in a shorter period if necessary (easily in 3 hours, possibly in 2).
Lab notebooks were collected and graded for all students. In addition to a condensed introduction and thorough lab procedure/observations section, students analyzed their x-ray data and submitted calculated particle sizes for their ferrofluids. They compared their measured particle size and rates of ammonia addition with the rest of the class via GoogleDrive. Each student wrote a short conclusion and discussion of experimental error and answered the postlab questions.
Students calculated reasonable particle sizes based on their x-ray data (we had planned to verify their measurements by SEM, but had instrument difficulties and were unable to do so), and made clear observations of their lab procedure. Most students were very excited to play with the ferrofluids and to use a new laboratory technique (XRD) to measure their samples, and comparing their data with the class results added an extra level of interest to the experiment.