Teachers may want to conduct this demonstration to show how varying the proportions of the two gases affects the resultant bang when the balloon is ignited. As an end of term or 'filler' lesson, teacher may just want one balloon filled with a mixture of two parts hydrogen to one part oxygen (the best mix for the biggest bang).
Teachers may require balloons filled with just air, just hydrogen, just oxygen, air and hydrogen and oxygen and hydrogen to compare the differences when ignited. This will obviously take some setting up. Gases from cylinders are required instead of chemically generated gases as it is difficult (but not impossible) to achieve sufficient pressure to inflate a balloon using the latter.
Small round party balloons should be used for this demonstration and they should not be filled too far in advance of the demonstration.
Equipment typically required (per demonstration)
Once filled, the balloons are ignited one at a time. The balloon is anchored securely to a clamp stand and lit with a taper attached to the free end of a metre rule.
- Party balloons (small)
- Metre rule with taper attached to one end
- Safety screen
- Eye protection
- Ear defenders
- clamp and stand
- Oxygen (oxidising agent)
- Hydrogen (Extremely flammable)
Always ensure there is nothing combustible directly above the balloon or near to it on the bench.
Some of the balloons will explode with an almighty bang and so it may be useful to have a go at this demonstration first without an audience.
Students should either wear defenders or place their fingers firmly in their ears to protect them from the bang. The demonstrator should wear eye and ear protection.
The equation for this exothermic reaction is:
2H2(g) + O2(g) → 2H2O(g)