This sub unit develops on what the student has learned from Visible Holes and focuses on Invisible Holes. To understand the existence of invisible holes and processes of substances being able to pass these holes, students have to enter the world of particles. To introduce them to this “new world”, surprising and fascinating phenomena are used, such as the “sieving of different dyes”. Following this, the students are invited to develop a series of experiments to investigate properties of sieves, particles and diffusion processes.

This can be followed by questions whether all membranes (plastics) are the same (Activity 2.1). Different polymer films can be investigated and polymer films can be made with different levels of plasticizer and retested (Activity 2.5).  Do they all have the same structure? Additionally, different compounds can be used on the same films to determine the pore size (Activity 2.2).

As an application, the leaching of plasticisers from packaging will be explored and can link to food packaging and possible hazards (Activity 2.5). Leading questions throughout the unit allow the students to progress from activity to activity as well as develop activities of their own.

Students can examine the uses of holes in dialysis membranes, in polymers used for absorbance, and in other polymer packaging materials.

Student level: 
Mid secondary school level, students of age 13-15