International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

How can you test for the presence of hydrogen gas?

1. By using a lit splint to check for a pop sound

2. By exposing it to a flame to check for combustion

3. By observing a color change in litmus paper

4. By measuring its density with a scale

The correct answer is: By using a lit splint to check for a pop sound

The presence of hydrogen gas can be tested by using a lit splint to check for a pop sound. This is a classic method in chemistry known for its simplicity and reliability. When hydrogen gas is ignited, it reacts with oxygen in the air to produce water vapor, and this reaction is highly exothermic. The characteristic "pop" sound that occurs is due to the rapid expansion of gases from the reaction, which creates a small explosion. This auditory signal is a clear indicator of hydrogen. Other testing methods mentioned, while valid for other gases or substances, do not specifically indicate hydrogen. For example, exposing hydrogen to a flame may not produce a specific identifiable sound, making it less reliable for distinction. Observing a color change in litmus paper is inappropriate, as hydrogen is a neutral gas and does not affect acid-base indicators. Measuring density would also not provide direct evidence of hydrogen's presence, as density alone is not a qualitative test for gases without context or comparison. Therefore, the lit splint test is the most effective way to confirm hydrogen gas.