Potassium chlorate (KClO3) is a useful compound that finds application as an oxidizer, oxygen source, disinfectant, safety match ingredient, firework material, and plant fertilizer. You can buy it, but it’s easy to make potassium chlorate at home using ordinary household bleach (sodium hypochlorite) and salt substitute (potassium chloride).
Potassium Chlorate Materials
You only need two ingredients and some type of filter to make potassium chlorate:
- Chlorine bleach
- Potassium chloride salt substitute
- Coffee filter or filter paper
Be sure to use salt substitute and not “lite salt.” Salt substitute is pure potassium chloride, possibly with a little anti-caking chemical that won’t cause a problem. Lite salt is a mixture of sodium chloride (table salt) and potassium chloride. Lite salt won’t work well because you need potassium to replace the sodium from the bleach to get potassium chlorate.
While not critical, it’s best to use fresh bleach for this project. This is because bleach has a shelf life and decomposes over time, eventually becoming salt water.
Make Potassium Chlorate
- The first step is to convert sodium hypochlorite in bleach into sodium chlorate and sodium chloride. Boil a large volume of bleach (at least half a liter) until crystals start to form. Boiling releases some chlorine compounds into the air, so do this step outdoors or under a fume hood to minimize breathing vapors.
3 NaClO → NaClO3 + 2 NaCl
- As soon as you start to see crystals forming, remove the bleach from heat and let it cool.
- In a separate container, make a saturated potassium chloride solution. To do this, stir salt substitute into water until no more will dissolve.
- Mix equal volumes of the boiled bleach solution and potassium chloride solution. Only mix the liquids together, so avoid getting any crystals or undissolved solid from either solution into the mixture. Mixing the solutions leads to a type of chemical reaction called an exchange or metathesis reaction. The potassium and sodium ions switch places, changing sodium chlorate into potassium chlorate:
KCl + NaClO3 → NaCl + KClO3
The sodium chloride is much more soluble in water than the potassium chlorate is, so it will fall out of solution or precipitate.
- Cool the solution in the freezer. This increases the yield of potassium chlorate.
- Finally, filter the solution through a coffee filter or filter paper. Keep the solid, which is the potassium chlorate. Discard the liquid, which is salt water.
- Let the potassium chlorate dry before using it. Store it in a sealed container until use.
Potassium Chlorate Projects
Here are some interesting potassium chlorate projects to try:
- Make purple fire: Mix two parts potassium chlorate to one part sugar to get purple flames.
- Instant chemical fire: You can ignite the mixture of potassium chlorate and sugar with a drop of sulfuric acid (no match or spark needed).
- Make oxygen gas: Chemistry labs often use potassium chlorate to make oxygen. Heat potassium chlorate together with manganese(IV) dioxide (a catalyst) over a burner. Siphon off the oxygen:
2 KClO3(s) → 3 O2(g) + 2 KCl(s)
Oxygen also forms if you simply heat potassium chlorate until it decomposes, but this type of chemical oxygen generator is risky because too much energy can be released too quickly.
- Dancing charcoal or dancing gummy bear: Heat a small amount of potassium chlorate in a test tube (which produces oxygen gas). Drop in either a small piece of charcoal or a gummy candy and watch it “dance.”
- Make crackers or bang snaps: Wrap together silver fulminate, coarse sand, and potassium chlorate in a paper wrapper to make snappers. Silver fulminate is unstable, so only work with tiny amounts.
Commercial Potassium Chlorate Productions
While the reaction between bleach and salt substitute is quick and easy, it’s not very efficient. Industrially, the Liebig process forms potassium chlorate by reacting chorine gas over hot calcium hydroxide to get calcium chlorate. Adding potassium chloride to get the calcium and potassium ions to switch partners:
6 Ca(OH)2 + 6 Cl2 → Ca(ClO3)2 + 5 CaCl2 + 6 H2OCa(ClO3)2 + 2 KCl → 2 KClO3 + CaCl2
Potassium chloride electrolysis also yields potassium chlorate. Electrolysis of KCl in water forms chlorine at the anode, which reacts with potassium hydroxide (KOH) in the liquid. Potassium chlorate formed by the reaction precipitates out of solution.
Passing chlorine gas over a hot potassium hydroxide solution also produces potassium chlorate, along with potassium hydroxide and water:
3 Cl2(g) + 6 KOH(aq) → KClO3(aq) + 5 KCl(aq) + 3 H2O(l)
This project should only be performed by adults because it involves boiling (heat) and because bleach is an eye, skin, and respiratory system irritant. Be sure to store potassium chlorate away from sulfuric acid or sulfur (which always contains a bit of sulfuric acid).
- Patnaik, Pradyot (2002). Handbook of Inorganic Chemicals. McGraw-Hill. ISBN 0-07-049439-8.
- Seidell, Atherton; Linke, William F. (1952). Solubilities of Inorganic and Organic Compounds. Van Nostrand.
- Zumdahl, Steven S. (2009). Chemical Principles (6th ed.). Houghton Mifflin Company. ISBN 0-618-94690-X.