Activity 2.1 - Membranes with invisible holes

• To draw conclusions from observations
• To explain the phenomenon through the existence of invisible holes and the movement of particles
• To distinguish alternative explanations and debate with peers

The teacher could either demonstrate the phenomenon as shown in the underlying experiment and let the students develop questions or start with a context of wrapping food. Worksheet 2.1 offers a possibility to investigate different plastic wrappings. Examples of investigations could be:

1. Iodine diffusing into a soluble starch solution

(i) No membrane

(ii) Jam pot cover

(iii) Plastic bag/cling film

(iv) Latex glove

2. Vinegar diffusing into water with Universal indicator

(i) No membrane

(ii) Jam pot cover

(iii) Cling film/ roasting bag

Students match results to models of particles.

The teacher could either demonstrate the phenomenon as shown in the underlying experiment and let the students develop questions or start with a context of wrapping food. Worksheet 2.1 offers a possibility to investigate different plastic wrappings. Examples of investigations could be:

Teacher should encourage a discussion of possible reasons and let the students deal with and encourage the development of the idea of particles of different sizes or membranes with holes of different sizes as one explanation.