HYDROGEN BALLOON
It is possible to fill a balloon with hydrogen safely in the lab, see the balloon
floating and again safely, ignite the gas.
You need :
1 250 mL conical flask with a ‘pronounced lip’
about 100 mL of 1 to 2 mol L-1 NaOH
1 round balloon
1 A-4 size sheet of Al foil
Cotton thread
1 ice cream container with cold water
1 taper candle (or) on a long stick
 Use at least a 250 mL conical flask, preferably with a fairly
pronounced ‘lip’ on it.
 Place 1.5 to 2 cm depth of 1 or 2 mol L-1 NaOH in flask.
 Obtain 1 A4 sized sheet of Al foil, tear this into strips and loosely
crumple into small balls.
 Obtain a round balloon (preferably not from the $2 shop) and blow it
up to stretch the balloon. Let it down again.
 Place the crumpled Al foil into the flask and wait for the reaction to
start. This can be quite slow, (3 – 4 minutes). Be patient at this stage.
 Once the reaction has started, place a balloon over the neck of the
flask.
 The reaction will then become very exothermic. Once the reaction is
underway, stand the flask in an ice cream container with 5 cm depth of
cold water.
 Once the reaction has ceased (5 minutes) due to the Al foil having all
reacted, remove the balloon and tie it off using a knot in the neck of
the balloon. Cut off any surplus balloon rubber and tie some light
cotton thread around the neck of the balloon. The balloon will inflate
almost to about a 15cm diameter.
 The balloon should float.
 You can safely ignite the balloon full of hydrogen, but since this has no
oxygen the reaction is not an explosion, but still a significant reaction.
Graeme Tinkler- Cashmere H/S