Rochelle salt or potassium sodium tartrate is an interesting chemical that is used to grow large single crystals, which are attractive and interesting, but also may be used as transducers in microphones and grammophone pickups. The chemical is used as a food additive to contribute a salty, cooling taste. It is an ingredient in useful chemistry reagents, such as as Fehling's solution and Biuret reagent. Unless you work in a lab, you probably don't have this chemical lying around, but you can make it yourself in your own kitchen.Make Rochelle Salt
You will need:- Cream of Tartar
- Washing Soda or Sodium Carbonate (which you can get by heating baking soda or sodium bicarbonate in a 275°F oven for an hour)
- Heat a mixture of about 80 grams cream of tartar in 100 milliliters of water to a boil in a saucepan.
- Slowly stir in sodium carbonate. The solution will bubble after each addition. Continue adding sodium carbonate until no more bubbles form.
- Chill this solution in the refrigerator. Crystalline Rochelle salt will form on the bottom of the pan.
- Remove the Rochelle salt. If you redissolve it in a small amount of clean water, you can use this material to grow single crystals.
Photo: Rochelle salt crystal grown on Skylab (NASA)
Comments
It has to be “real” cream of tartar, potassium bitartrate. There’s a cheap substitute that uses some other acid and corn starch to make it act like cream of tartar in cooking. But it does NOT work to make rochelle salt. I’ve bought Cream of Tarter from a lot of different sources, and haven’t been able to get this recipe to work. It stops fizzing after I’ve added about 1/4 of the Sodium Carbonate, and the solution is amber colored, probably from the corn starch. Apparently every cooking store is now selling the cheap substitute.
One possible reason for this is that Rochelle salt is might be an ingredient in some designer drugs, and the DEA has asked them to stop selling the real stuff. Or more likely, in today’s business climate where everybody is cutting costs, they’re just selling the cheap stuff because they can get away with it.
It’s possible to obtain potassium bitartrate or cream of tartar by collecting the crystals that precipitate from fresh grape juice that is chilled and undisturbed. The chemical crystallizes from wine also.
Try a homebrew shop. We use Potassium Bitartrate in winemaking to settle out excess tartaric acid. I know it’s available from Presque Isle Winery, piwine.com.
I know Mic cormick sells actual cream of tartar (Potassium bitartrate) as I’ve made KNaC4H4O6 from it in the past.
If you are using Sodium carbonate made from baking soda in the oven (anhydrous) you’ll need to add 22.529 grams to the 80 grams of Potassium bitartrate, but if you are using washing soda bought from the store (decahydrate) you’ll need to add 60.824 grams of Sodium carbonate.
I have tried it two times and it didn’t work the solutions crystallized or hardened but didn’t formed into crystal. Is there online stores that sells the Crystal to buy for Science project instead of retrying????