Summary

Pea sized portions of potassium chlorate and red phosphorus are reacted together by striking with a hammer. Smoke, a loud bang and a flash are observed.

Hazards

• The mixture of potassium chlorate and red phosphorous is shock sensitive!!
• DO NOT STIR THE DRY POWDERS TOGETHER.
• DO NOT USE MORE THAN PRESCRIBED PEA SIZED AMOUNTS.
• KClO is a strong oxidizer. Do not grind the KClO₃.
• Red phosphorus is highly toxic and flammable.

Chemicals and Solutions

• Potassium chlorate, KClO₃ (same size as in #1)

Materials

• Transite board
• Spatula
• Hammer

Procedure

1. Using spatula place a small amount of red phosphorus onto the transite board.
2. Using a clean spatula, carefully place a small amount of potassium chlorate onto the red phosphorus, so that the two match sized piles are touching.
3. THIS MIXTURE IS SHOCK SENSITIVE. DO NOT STIR THE DRY POWDERS TOGETHER.
4. Strike with hammer. A sharp fire cracker like noise, sparks (flaming bits of phosphorus) and smoke are produced.

Hint: Don’t wear your favorite shirt for this demo. Lab coat and goggles are recommended.

Discussion

$$\ce{ 3P4_{(s)} + 10KClO3 -> 3P4O10_{(s)} + 10KCl_{(s)} }$$

$$\ce{ P4 ~~~~~~~ \Delta G = -12.1 kJ/mol }$$

$$\ce{ P4O10 ~ \Delta G = -2697.7 kJ/mol }$$

$$\ce{ KClO3 ~\Delta G = -296.25 kJ/mol }$$

$$\ce{ KCl ~~~~~ \Delta G = -408.77 kJ/mol }$$

$$\ce{ Total ~~~ \Delta G = -9182 kJ/mol }$$

The head of "strike anywhere" matches contain an oxidizing agent such as potassium chlorate together with tetraphosphorus trisulfide, P₄S₃, glass and binder. The phosphorus sulfide is easily ignited, the potassium chlorate decomposes to give oxygen, which in turn causes the phosphorus sulfide to burn more vigorously.

The head of safety matches are made of an oxidizing agent such as potassium chlorate, mixed with sulfur, fillers and glass powder. The side of the box contains red phosphorus, binder and powdered glass. The heat generated by friction when the match is struck causes a minute amount of red phosphorus to be converted to white phosphorus, which ignites spontaneously in air. This sets off the decomposition of potassium chlorate to give oxygen and potassium chloride. The sulfur catches fire and ignites the wood.