Identification of Gases

This lesson covers the tests for common gases as required by the AQA GCSE Chemistry specification (8.1.2). You need to know how to test for and identify hydrogen, oxygen, carbon dioxide, and chlorine. These gas tests are fundamental to chemical analysis and appear regularly in exams — both as standalone questions and within the context of reactions that produce gases.

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Why Do We Test for Gases?

Gas tests allow chemists to:

• Identify unknown gases produced in chemical reactions.
• Confirm that a predicted reaction has taken place.
• Monitor industrial processes.
• Ensure safety — some gases (e.g., chlorine) are toxic.

You must be able to describe the test AND the positive result for each gas.

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Test for Hydrogen (H\u2082)

Feature	Detail
Test	Hold a burning splint near the mouth of the test tube containing the gas
Positive result	The hydrogen burns with a squeaky pop
Why it works	Hydrogen is flammable and reacts explosively with oxygen in the air: 2H\u2082 + O\u2082 \u2192 2H\u2082O

When Hydrogen Is Produced