Test for hydrogen using a lit splint
Chemical analysis • Identification of common gases
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Definition and purpose of the test
Hydrogen gas is a colourless, odourless, flammable gas. The lit-splint test identifies the presence of hydrogen by producing a distinctive auditory signal rather than a colour change. The test aims to confirm hydrogen quickly using minimal apparatus and a visible/audible effect. The test does not measure concentration precisely. Very small amounts of hydrogen may produce a weak or absent sound, and large uncontrolled volumes create a fire hazard. Controlled sample sizes and adherence to safety precautions ensure a clear result.
Apparatus and setup
Apparatus includes a test tube or gas collection container, a method to collect the gas (displacement of water or direct collection), and a wooden splint that can be ignited. The splint should be lit, then blown out to leave a glowing ember rather than a full flame to reduce risk and improve control. The gas sample sits near the mouth of the container. The lit splint is held close enough to interact with escaping gas but not inserted deeply. Correct setup prevents premature ignition inside the tube and limits the amount of gas that can ignite, reducing hazard.
Observation and chemical explanation
The primary observation is a sharp ‘squeaky pop’ or small explosive sound when the glowing splint meets the escaping gas. The sound occurs because hydrogen reacts rapidly with oxygen in air: 2H2 + O2 → 2H2O. Rapid combustion releases energy and causes a brief expansion of gases, producing the audible pop. The presence of the pop indicates hydrogen combined with oxygen to form water vapour. No pop suggests hydrogen is absent, present in very low concentration, or that the test was not performed correctly (for example, wrong splint position or insufficient gas sample).
Limitations and safety considerations
The test gives a qualitative result only. The pop sound confirms hydrogen but does not quantify purity or concentration. Other experimental errors can lead to false negatives, such as leaks, dilution of the gas, or using a full flame rather than a glowing splint. Safety considerations include using small gas volumes, wearing eye protection, keeping flammable materials away, and ensuring good ventilation. Large accumulations of hydrogen present explosion risks, so controlled, small-scale testing prevents dangerous outcomes.
Key notes
Important points to keep in mind