This list provides a range of activities and demonstrations, together with background information and suggested teaching strategies, which explore diffusion. The use of models and analogies here can aid understanding and students should be challenged to use a simple particle model to explain what they observe.
The resources link to following statements in the curriculum:
• diffusion in terms of the particle model
• diffusion in liquids and gases driven by differences in concentration
• Brownian motion in gases
Visit the secondary science webpage to access all lists: www.nationalstemcentre.org.uk/secondaryscience
Links and Resources
This resource shows you how to carry out the classic demonstration on diffusion where two invisible gases travel down a tube from opposite ends and react where they meet to form a white solid. When you open the file, scroll down the list then click on “diffusion”.
It’s recommended that you talk through the reaction with students before starting this demo. You can mix the two solutions together and show that they react to produce a new white solid. In this situation it is helpful to refer to the hydrochloric acid as a solution of hydrogen chloride. Students should be able to write a word equation for the reaction and more able students will be aided in their understanding by seeing the symbol equation. This way, pupils will have a better understanding of what is happening when they see the white “smoke” form.
When carrying out the demonstration, minimise the time delay between inserting the cotton wool in either end by preparing both beforehand and leaving them on the petri dish until needed.
Challenge the class to explain why the solid doesn’t form in the middle of the tube. There’s no need to discuss molecular mass at this level, but most should appreciate that the ammonia must have travelled more quickly than the hydrogen chloride.
You can ignore the “read me” file since it refers to the DVD which was originally sent out to schools. The accompanying safety notes simply refer you to the hazchem cards 6 and 47a and may now be out of date.
Chapter five of this resource provides a series of student experiments designed to reinforce the concept of diffusion. There are both teacher notes and student worksheets here to use although teachers may want to produce their own updated student worksheets based on these.
Activity two (coloured crystals in solid gelatin) is particularly recommended since it is so visible. The experiment works equally well in petri dishes of agar where it is probably easier to observe and where holes can be made with straws instead of cork borers. However, the other three activities are worth doing too and taken together this would be a good hands on lesson for students to experience diffusion for themselves.
Perfume is often used to teach diffusion since if you can smell it then the particles must have travelled to your nose. If you have plenty of time, you might like to work through this whole sequence of these activities where students extract their own scents and develop their literacy skills by writing for a teenage magazine.
However you could base a just single lesson around this resource, finishing off a topic on diffusion and the particle model with students using steam distillation to extract the smelly molecules in orange peel. Students will enjoy developing their practical skills and teachers could challenge them to explain how they can smell their resulting product.
Usefully two versions of the student sheets are provided. Choose the version most suitable for how you want to run the lesson and the ability of your students.
Chromatography is often taught as a means of separating mixtures but it also shows diffusion in action and is strong evidence for the particle theory of matter. You’ll need to install the software on your own computer before using it but it's worthwhile because there’s plenty of good stuff here that you’ll almost certainly want to use in other lessons too. For this topic choose main resources and then scroll down to chromatography.
After students have set up chromatograms with felt pens or food colouring, this resource would be good to use while they wait for their chromatograms to run. Teachers will find the animation useful as they talk through what is happening at the particle level. However, few labs will have access to class sets of equipment capable of raising the beaker to meet the solvent as shown in their diagram! The speeded up film will help students to appreciate the whole process
This short video shows how Brownian Motion can be demonstrated using polystyrene balls rather than a smoke cell. Careful explanation is needed throughout this demonstration so that students do not think that the moving dots they see under the microscope are atoms or molecules.