Easy-to-grow Rochelle salt crystals are much larger than table salt and way more fun to look at! But these crystals also have important jobs to do: Rochelle salt has been used as a mild laxative, in the process of silvering mirrors, and for its piezoelectric properties. Grow your own Rochelle salt overnight using the simple solution in this chemistry project.
***If you want to experiment further, don’t discard the solution you pour off. Keep it in a clean dry beaker.
For further study, grow one large single Rochelle salt crystal that you can use to experiment with. After completing step 7 above, find your largest crystals. Important: use forceps or tweezers—not your fingers. Carefully knock off any tiny pieces of crystal growing off the large ones so that the remaining crystal is smooth. Being sure not to disturb the solution, gently lower the large crystals (seed crystals) into the beaker. Place it in the refrigerator and leave it undisturbed for a week or longer; the longer you leave it, the bigger your crystals will be! When you check it, you should find several very large Rochelle salt crystals! The crystals below were grown in about two weeks.
A crystal is a hard, solid substance made of molecules that bond together in specific patterns to form a shape with straight edges and flat surfaces. Not all crystals have the same shape or size. The site where a crystal begins to grow, called its nucleation site, determines its size: fewer nucleation sites mean larger crystals, and many nucleation sites produce smaller crystals. Here, you made Rochelle salt crystals, the potassium sodium tartrate that precipitated out from your saturated solution. The process of precipitation in chemistry refers to a solid forming or precipitating within a liquid solution. The most common type of precipitate found is crystallization.