Saturday, January 2, 2010

Make Potassium Nitrate from Lite Salt

Potassium nitrate (saltpeter) is used for many chemistry projects, most notably for making smoke bombs. I've talked about how you can obtain potassium nitrate at a store or online, but you could make it yourself from easy-to-find ingredients. NurdRage has a YouTube video of this simple inorganic chemical reaction (as well as many other cool chemistry videos).
Potassium Nitrate Ingredients
  • 40 g ammonium nitrate (from an instant cold pack which has ammonium nitrate listed as its ingredient)
  • 37 g potassium chloride (sold as a salt substitute, with potassium chloride listed as the ingredient)
  • 100 ml water
Make Potassium Nitrate Aqueous solutions of ammonium nitrate and potassium chloride are reacted to exchange the ions and form potassium nitrate and ammonium chloride. The ammonium chloride is much more soluble in water than the potassium nitrate, so you will get potassium nitrate crystals, which can be separated from the ammonium chloride solution.
NH4NO3 + KCl → KNO3 + NH4Cl
  1. Dissolve 40 g of ammonium nitrate into 100 ml of water.
  2. Filter the solution through a coffee filter to remove any undissolved material.
  3. Heat the solution with 37 g potassium chloride to dissolve the lite salt. Do not boil the solution.
  4. Filter the solution and either set it in the freezer to chill or else put it in an ice bath so you can observe the crystallization of the potassium nitrate.
  5. Pour off the ammonium chloride solution, leaving the potassium nitrate crystals. You can recover the ammonium chloride, too, if you like.
  6. Once the potassium nitrate crystals are dry, you can use them for chemistry experiments. The resulting potassium nitrate does contain impurities, but it will work fine for pyrotechnics projects and other experiments described on this site.

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