Get the kids to make your cup of tea: Investigating Teabags!

I love a good cup of tea. In fact I cannot actually function without one first thing in the morning. If you’re like me, then this investigation is definitely needed in your house, so that you can ensure your kids are equipped with the best tea making skills and have the best scientific knowledge to back up what makes a good cup of tea! This investigation looks at diffusion through a partially permeable membrane.

So firstly we want to know what type of teabag makes the best drink?

Is is a square, a pyramid or a circle bag?

What you will need

A stopwatch/timer (most mobile phones have them on now)

A piece of white paper

A pen

3 clear glass or plastic cups (you are going to add hot water, so not thin ones that could crack)

Circle, triangle and pyramid tea bags

Thermometer or kettle

Method

1. On the piece of white paper draw a cross with a marker pen

2.Place the glass over the cross

3. Add the circle bag

4. Boil water from the kettle  and measure out 150ml (if you have a thermometer you can improve reliability by keep the temperature constant)

5. Pour over the teabag and start the stop watch

6. Time how long it takes for the cross to disappear

7. Repeat with the pyramid and square bag.

8. To make the investigation results more accurate repeat with each teabag three times.

Record your results in a table

Results explained

So which teabag was quicker?

You should find that the pyramid teabag was the quickest.

Why do you think this is?

As the water is added to the teabag it causes the tea leaves to move and triggers diffusion of the leaves. Diffusion is defined as the movement of a substance from an area of higher concentration to an area of lower concentration. There are lots of tea molecules in the bag and none outside. The leaves themselves can’t pass through the bag but their  smaller particles containing colour and flavour can (the teabag itself acts as the partially permeable membrane). The addition of heat (from the hot water) to the tea bag causes its molecules to move much faster than at room temperature. This energy is more readily released in a shorter period of time than a tea bag filled with room temperature or cold water. The teabag shape affects the surface area and the pyramid due to it 3D shape provides more sides for diffusion to take place and more area in the middle for the tea molecules to move around in spreading the stain of colour.

Ok, so now they know which is the best teabag to use and how to let it brew…so I suggest you ask for a nice cuppa now!