Diffusion of gases on a microscale

An illustration with red and blue circles representing particles of two gases mixing

Source: Royal Society of Chemistry

Try this class practical to explore the diffusion of gases and how relative molecular mass affects rate of diffusion. Includes kit list and safety instructions.

In this experiment, students observe the diffusion of ammonia and chlorine gases as a result of their interaction with copper(II) sulfate and potassium iodide/starch solutions. They look out for colour changes and patterns as the gases react with drops of the test solutions, and record their observations.

The practical is suitable for various levels with differing degrees of interpretation. For example, by reflecting on their observations, students can develop their understanding of the properties of gases, considering rate of diffusion as a function of relative molecular mass.

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