These instructions are modified from the experimental details in Berger et al, Journal of Chemical Education, 1999, 26, 7, 943-948. This experiment is only appropriate in a lab environment with personal protective equipment and a fume hood for the ammonium hydroxide step. For all safety information – see the links to the MSDS files listed below. Make sure you complete your own risk assessment.
Step 1 – prepare solutions
Dissolve 67.58 g FeCl3.6H2O in 250 ml of 2 M HCl. (Material Safety Data Sheet)
Dissolve 39.76 g FeCl2.4H2O in 100 ml of 2 M HCl. (Material Safety Data Sheet)
Both solutions should be used within a week of preparation
Step 2 – Add ammonium hydroxide
Caution: Ammonium hydroxide solution is corrosive, harmful and dangerous to the environment. The vapours are also very unpleasant so it’s best to do this in a fume hood. (Material Safety Data Sheet)
Combine 3 ml of FeCl2 solution with 12 ml of FeCl3 solution in a flask and fill a burette with 150 ml of 0.7 M ammonium hydroxide solution.
Add ammonium hydroxide very slowly whilst stirring. A burette or dropping funnel works well for this. A black precipitate of magnetite (Fe3O4) will form.
Step 3 – Collect and wash the magnetite
After addition of ammonium hydroxide is complete, stop stirring and use a strong magnet (e.g. a neodymium iron boride magnet) to settle the black precipitate to the bottom of the flask. Decant off the water and add fresh deionized water. Rinse the precipitate and again decant off the water. Repeat three times to remove excess ammonia.
Step 4 – Functionalize the magnetite particles
Transfer the viscous liquid to a weighing boat using a little extra water if necessary. Use a magnet on the base of the weighing boat to hold the particles while you decant off any excess water. Take away the magnet and add 24 ml of tetramethylammonium hydroxide (25% solution) then stir with a glass rod.
Caution: Tetramethylammonium hydroxide is toxic (Material Safety Data Sheet)
Step 5 – The ferrofluid
Hold a magnet on the base of the weighing boat and let the solid settle to the bottom. Decant off any excess liquid to leave a very viscous black liquid. The viscous liquid should form spikes if a magnet is held underneath the weighing boat. You may need to adjust the amount of water.
NOTE: You need to use a very strong magnet for this to work. A normal magnet will just give you a ‘bubble’ rather than the spikes.
For some beautiful ferrofluids in action, try looking up ‘ferrofluid sculpture’ on Youtube, e.g. this one!
Schneppgroup images by Zoe Schnepp is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.