Thursday, 15 November 2007

DIY Hydrogen Plant

In this post we'll be looking at a way of making hydrogen from some basic kitchen ingredients. Many thanks to Aston for helping me out with this project.

You will need...
  • Aluminium foil
  • Caustic soda. Check the packet and make sure you are buying sodium hydroxide.
  • A glass bottle. Glass is far better than plastic as it is going to get very hot.
  • Rubber gloves
  • Old clothes
  • A garden
  • Party balloons

1) Change into your old clothes and put on the rubber gloves. Caustic soda is nasty stuff and you don't want to get it over yourself.
2) Fill the glass bottle around a third full with cold water.
3) Add caustic soda crystals a little at a time. Shake the bottle every time you add more crystals to dissolve them. When the water starts to become cloudy and there are crystals left in the bottom of the bottle stop adding - the water has become saturated and there isn't any point putting any more in. Feel the bottom of the bottle. Does it feel warm?
4) Make some aluminium foil torpedoes that you can drop into the neck of the bottle.
5) Drop some torpedoes into the bottle, give the bottle a swirl and then wait for a few

You should start to see the aluminium start to fix and bubble. The water will get very hot and may well start to boil. You should see wisps of steam coming out of the top of the bottle.

If you have a balloon handy then pull it over the top of the bottle and watch it inflate...

Tie off the balloon and let it go. It floats away!

The balloon is full of hydrogen. Apart from being lighter than air hydrogen has another interesting property to all of us kitchen experimenters - it's highly explosive!

As the reaction is going on, put a lit match to the top of the bottle. What happens?

How does that work then?

Sodium hydroxide and aluminium react very strongly with each other. So why the slight delay before the reaction starts in earnest? That's because the foil will be coated with a thin layer of oxide, which the soda has to react with before we get to the reaction with the aluminium proper...

2Al(s) + 6NaOH(aq) → 3H2(g) + 2Na3AlO3(aq)

For the non-chemically minded, that's lots of hydrogen - H2(g)!

The reaction between aluminium and caustic soda is exothermic. This means that it gives out (a lot of) heat.

And remember: hydrogen filled balloons may be fun to play with, but this is the sort of thing that can happen if you are not too careful...