Hydrogen is a colourless gas with no smell, so we cannot identify it by looking at it. We use a chemical test instead. The test for hydrogen uses a burning splint.
Collect the gas in a test tube. Hold a lit splint at the open end of the tube. If the gas is hydrogen, it burns rapidly with a squeaky pop sound. The pop is a small explosion as the hydrogen burns with oxygen from the air.
The hydrogen reacts with oxygen to make water: 2H2 + O2 → 2H2O. This is why hydrogen is described as a clean fuel, because the only product is water.
The test needs a lit splint, not a glowing one. Other gases such as nitrogen or carbon dioxide do not pop. They simply put the flame out.
