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Use iodine to test the amazing property of semi-permeability

Suitable For

Grade 2



Time Required

 <12 Hours



What’s it about?

Semi-permeability is the ability of a material to allow only a certain size of molecule to pass through it. The walls of animal and plant cells both have this property to be able to feed themselves, and at the same time remove waste as well as protect them from substances that might be harmful to them. This science experiment demonstrates the amazing property of semi-permeability:

Topics covered

Permeability, Indicator, Iodine

What will I need?


Procedure (Method)

Unfortunately, this section is only available in the e-book version of the project.

How does it work?

Unfortunately, this section is only available in the e-book version of the project.

In this science experiment we use a chemical reaction that changes the colour of an ‘indicator’ (iodine) in the presence of ‘starch’. When the iodine in the bowl comes in contact with the starch-water in the bag, a deep purple-blue coloured substance is formed inside the plastic bag, indicating that the iodine has penetrated through the permeable bag and turned blue in the presence of starch.

A starch molecule is one of the largest, most complex, food molecules and due to its size, it cannot penetrate through the bag back into the bowl of water; hence the light yellow colour of the iodine water in the bowl remains the same. The plastic bag acts as a cell wall letting in the ‘simple’ iodine molecules, but the large starch molecules could not pass through.

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