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.