3.12 - Tests for hydrogen and carbon dioxide
Learn how to distinguish two colourless gases using a chemical test: hydrogen gives a squeaky pop with a lighted splint, while carbon dioxide turns limewater cloudy. You will connect each method to its observation and explain why a flame going out is insufficient evidence.
Testing for hydrogen
Collect a small sample of gas in a test tube, then hold a lighted splint at its mouth. Hydrogen burns rapidly with oxygen from the air and produces a squeaky pop. A glowing splint is not the hydrogen test.
The reaction forms water:
Use only a small sample because hydrogen is flammable. Wear eye protection, keep the tube pointing away from people and keep the flame at the mouth, where the gas meets air.
Testing for carbon dioxide
Bubble the gas through limewater, a solution of calcium hydroxide. Carbon dioxide makes the limewater turn cloudy or milky because a fine white solid, calcium carbonate, forms.
The delivery-tube outlet must be below the limewater surface so that the gas bubbles through it. Use a small volume of limewater, avoid splashes and never suck liquid or gas by mouth.
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