How to Make Potassium Nitrate

How to Make Potassium Nitrate

Make potassium nitrate (saltpeter) from common household ingredients. Potassium chloride from salt substitute and ammonium nitrate from a cold pack are reacted to yield potassium nitrate and ammonium chloride. This is an easy way to make your own potassium chloride if you can't find it in a store or just want to try a fun chemistry experiment.

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 only ingredient)
  • 100 ml water

You should be able to find the ingredients at a grocery store or general store. Cold packs that work using ammonium nitrate contain two pouches. One is filled with water, while the other contains solid ammonium nitrate. Potassium chloride is a common salt substitute, used by people trying to cut their sodium intake. It's sold with table salt and other spices. While it's fine if there is an anti-caking chemical, you'll want to avoid lite salt containing both potassium chloride and sodium chloride because you'll end up with a mixture of sodium nitrate and potassium nitrate from the chemical reaction.

The Chemical Reaction

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. The chemical equation for the reaction is:

NH4NO3 + KCl → KNO3 + NH4Cl

Make Potassium Nitrate

  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.

Examples of Potassium Nitrate Science Projects

  • Perhaps the simplest project you can perform with potassium nitrate is producing purple fire. The purple color results from the excitation of the potassium ion. You could also mix potassium nitrate with alcohol to make a colored fire spray bottle.
  • Potassium nitrate is a key ingredient in a homemade storm glass, which produces crystals in response to atmospheric conditions.
  • Mix potassium nitrate with sugar to make a homemade smoke bomb.
  • Coat paper with a mixture of potassium nitrate and water, let it dry, and apply a match to write a message using fire.
  • Potassium nitrate is used to make black powder.