This is a quick and fun lab that will get lots of oohs and ahhs from your students. Two versions are included. One is for honors or pre-ap chem level and includes a mole or stoichiometry calculation. The other version is appropriate for on-level, middle school, or GTE elementary. You could also use it as an introduction to physical change in upper level chem classes.
Students make a small amount of a supersaturated solution of sodium thiosulfate. After cooling it, they drop a single seed crystal into the solution and watch the entire solution solidify around it. Most students will reheat and do it several times. It is a very engaging activity.
This is a physical change. The lab includes an introduction to supercooling and sodium thiosulfate and how it is produced.
Keywords: chemistry, experiment, supersaturated, supercooling, solidification, crystallization, moles, stoichiometry, Avogadro's number, physical change, crystal, ionic compound, ions, formula units.