Science Club – Diffusion

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Arrival Craft: Colour mixing sheet colourmixing

Introduction: One of the big rules of science is that things move from an area of high concentration to an area of low concentration. There is a basic sense of fairness about chemistry and substances like to spread themselves out as evenly as they can.

If we put a drop of water in the middle of a piece of filter paper, what will the water do?

The water will spread as far as it can, moving from an area of high concentration to an area of low concentration.

We can use this to separate out the colours of felt tip pens, this is called chromatography.


Individual Task: Give out felt tip pens and coffee filter paper so children can have a go at chromatography. chromatography


Break for drink and snack.


Second Half: Diffusion isn’t only good for finding the colours in felt tip pens. It can also be used to spread flavour around.

Why are the holes in tea bags the size that they are? What would happen if we had a tea bag without any holes in it? What would happen if we had a tea bag with huge holes in it?

To make this a bit more interesting, I put a normal tea bag in some water, then cut big holes in the side of another teabag and put that in water too. As the children predicted, the teabag with big holes in got tea leaves in the water.

We call the material that tea bags are made of a semi-permeable membrane. Membrane means skin or covering. Permeable means something that lets things through. Semi means some. So, semi-permeable membrane just means a covering that only lets some things through.

Individual Task: Make tea bags. This had the potential to get very messy! I put out bowls with different types of leaf tea, spices, and edible flowers. I gave the children empty teabags and encouraged them to mix their own special blends of tea.

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