Introduction

Balloons filled with hydrogen and containing metal salts are ignited.  When the balloon explodes, the characteristically colored flame for that metal is seen.

2H2(g) + O2(g) → 2H2O(g)

Supplies

Short List

  •   Time tape
  •   String
  •   Balloons
  •   Matches
  •   Earplugs
  •   Goggles
  •   Fire extinguisher
  •   Yardstick
  •   Candle

Chemicals

  •   Various metals (see “Test Flames” demo for salts)

Prior to Lecture  (prep time ~ ? min.)

1.     Fill desired number of balloons with small amounts (<0.5g) of desired metal salts.  See “Flame Test” demonstration for list of metals and the colors of their flames.

2.     Immediately before lecture, inflate balloons with hydrogen.  Attach ~6ft. strings to each.  Tape the ends of the strings to the floor or the lecture table at such a height that the balloons can be reached with the candle on the yardstick.

Assemble the following:

  •   Yardstick with candle attached
  •   Time tape

To Conduct Demonstration

  1. Caution the audience to cover their ears and to expect a loud explosion.  Wear earplugs if desired.

  2. Light the candle on the end of the yardstick and lower the lights.
  3. Bring the candle under the balloon until the tip of the flame touches the balloon.  Be prepared for an explosion.  DO NOT LIGHT THE STRING ON FIRE!

Reaction Time: Leave for the rest of the class period

Safety 

This is best performed outside or in a very large lecture room.  The explosions can shoot out salt particles, and the resulting smoke can be irritating.  Hearing damage can occur with especially large balloons.