My husband has been doing some science demonstrations with the kids recently. Here’s a picture from one of them. He used a 9 volt battery to separate water into hydrogen and oxygen. All that was required was adding a bit of magnesium sulfate (Epson salt) to the water and then dropping the battery in. He positioned two test tubes above the electrodes to collect the separated elements. Can you guess from the picture (and the formula of water) which test tube holds which?
He held a small candle to the hydrogen tube to hear it pop, and tried to use the oxygen tube to re-ignite an extinguished candle. Then he put the battery back in with a single jar on top to collect the mix of both hydrogen and oxygen. When a significant amount had accumulated he used a lit match to create an impressive burst of fire.