Here you will learn how to prepare Rochelle salt from baking soda and cream of tartar, which are available from a grocery store.
It will involve two chemical steps (reactions) prior to the actual growing of the crystal. The procedures are safe and can be conducted in your kitchen, with appropriate adult supervision.
The only restriction for the purposes of the Crystal Growing contest is that 200 g of cream of tartar is the MAXIMUM starting amount of that reagent that may be used to prepare a given crystal.
HERE's WHAT YOU NEED
NOTE: Some people have gone to bulk food or health food stores where they found a less expensive cream of tartar. Unfortunately, what is sold there as "cream of tartar" frequently has been NOT potassium bitartrate, but rather a mixture of calcium sulfate (Plaster of Paris), monocalcium phosphate, fumaric acid, and corn starch. This mixture definitely WILL NOT WORK. If the sales person cannot guarantee that what they offer is potassium bitartrate, don't buy it, at least for this purpose.
HERE's WHAT YOU DO FOR THE FIRST REACTION
This involves the conversion of baking soda (sodium bicarbonate)[NaHCO3] to sodium carbonate(washing soda)[Na2CO3]
HERE's WHAT YOU DO FOR THE SECOND REACTION
This involves the reaction of cream of tartar (potassium bitartrate formulation only)[KHC4H4O6] with sodium carbonate [Na2CO3] to produce Rochelle salt (potassium sodium tartrate)[NaKC4H4O6].
This should yield about 210 g of Rochelle salt.
You can now recrystallize your Rochelle Salt, by using a single good crystal obtained above or by making a seed crystal.
Now go to procedures for growing single crystals.
It will be helpful to know that about 60 g of Rochelle salt will dissolve in about 100 g of water at room temperature. As you warm the water, you can dissolve more Rochelle salt.
This procedure is adapted from that used by Malgorzata Kaminska, an Ottawa high school student, in her Science Fair project.