Department of Chemistry

Gun Cotton

pdf version

Although this little ball of soft goodness looks innocuous, apply a tiny spark (or heat source of any kind) and the fun begins! Gun Cotton is simply household cotton that has had specific sites on its molecular chain converted into an explosive! Reminiscent of TNT, the gun cotton will burn extremely fast. It all combusts into gases, leaving NO ASH! This is one of the students' favorites as THEY get to explode the cotton!

Materials Preparation

  • Concentrated H2SO4
  • Concentrated HNO3
  • Cotton Balls
  • Ice Bath
  • 250 mL Beaker
  • Ziploc Bag
  • Tongs

Presentation

  • Gun Cotton
  • Wire Coat Hanger
  • Glass Stirring Rod
  • Bunsen Burner (or Lighter)

Preparation

*The gun cotton should be prepared at least 2 days before the show.

Place a 250 mL beaker in an ice bath. Carefully combine 70 mL of concentrated H2SO4 and 30 mL of concentrated HNO3 in the 250 mL beaker.

Using tongs, place 6 cotton balls in the acid mixture.  Cover the beaker with a watch glass, and let it sit overnight in the ice bath.

The following morning, thoroughly rinse the cotton balls with water. One way to do this is to immerse each piece (using tongs) in three successive cups of water (~250 mL).  Use fresh water for each piece of cotton.

Place the gun cotton on paper towels in a safe location to dry.  Once they have dried, they should be stored in a Ziploc bag.

Presentation

Place a piece of gun cotton on the end of the wire coat hanger.

Heat the glass stirring rod in the flame for approximately 1 minute.

Have your partner hold the gun cotton on the wire, making sure to point it away from their body. Touch the hot glass rod to the cotton.

*This procedure was adapted from:Summerlin, L. R., Borgford, C. L., Ealy, J. B. Chemical Demonstrations; American Chemical Society:  Washington, DC, 1988; Vol. 2, pp 105-106.

Shakhashiri, B. Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry; TheUniversity of Wisconsin Press:  Madison Wisconsin, 1983; Vol. 1, pp 43-45.

Background

This demonstration deals with the conversion, storage, and release of energy.  Using chemical means, we are changing ordinary cotton into explosive gun cotton.  Cotton is made of cellulose, a naturally occurring polymer with the structure seen below.

Diagram

Concentrated H2SO4 activates the nitric acid, which then nitrates the cellulose. The final product is called trinitrocellulose and has -NO2 groups in place of the -OH groups, as seen below. 

Diagram

When the gun cotton touches the hot glass rod, the following decomposition reaction takes place:

Diagram

The products of this reaction are all gases, and therefore no ashes should be produced.

Safety Concerns

Use extreme care when handling concentrated nitric and sulfuric acids.  Immediately neutralize any spills with NaHCO3 and thoroughly rinse them with water.