You need aluminum, sodium hydroxide and some water. Then, also, a container like a flask, or a bottle (even a plastic bottle would do, but it should be hermetic). Also, the balloon itself. It would be good to have some hygroscopic/absorbent cotton wool (it would be helpful to stop the bubbles not going out of the bottle to the balloon), but it is not necessary if the neck of the bottle is high enough or the reaction speed is controlled. Also, you have to prepare some thread to close the balloon, but it is not necessary if you can close the balloon by making a knot.
- Create the water solution of sodium hydroxide
- Put it into the bottle
- Add aluminum into the same bottle
- Put the balloon on the neck of the bottle
- Wait and control reaction
2 Al(s) + 6 NaOH(aq) → 3 H2 (g) + 2 Na3AlO3(aq)
Using 54 grams (2 MOLs) of Aluminum you can produce 6 grams (3 MOLs) of hydrogen (H2), which will have 67.2 liters of volume under the atmospheric pressure. (Of course, because the balloon creates some pressure, the actual volume will be smaller.)
You don't have to worry much about the amount of water, but it is important to control the concentration of it, because during the reaction, if you add too little of water, it will be much likely that the bubbles (foam-like structure) will develop.
For 54 grams of Al you need 240 grams of Sodium Hydroxide.
- If you use the plastic bottle, it can start melting because of heat, so be prepared for cooling it (large amount of cold water would do)