What it shows
Particles move faster in hot water, so colour from a tea bag spreads, or diffuses, much faster there than in cold water. Measuring the time to colour a glass shows how temperature affects diffusion and dissolving.
The science
Water and tea molecules are always moving, and the movement is faster when it is hotter. Fast water molecules knock tea particles out of the leaves and spread them through the glass quickly. In cold water the same process happens, but far more slowly, so the colour spreads in a thin plume.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- 3 identical tea bags
- 3 clear glasses
- Cold water, tap water and warm water, around 60 C (adult mixes)
- A stopwatch
- A white paper to put behind the glasses
- A thermometer
- A notebook
Safety
For this project: An adult must heat the water and pour it. Warm water above 50 C can scald, so children should not pour it.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
7 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Fill glass 1 with cold water, glass 2 with tap water and glass 3 with warm water of equal volume.
Place a white paper behind the glasses to see the colour clearly.
Drop one tea bag in each glass at the same moment and start the stopwatch.
Note how long the colour takes to reach the bottom of each glass.
Take photos every thirty seconds for five minutes.
Compare the final colour darkness after ten minutes, not stirring the tea at any time.
Write a short statement linking the temperature to the speed of spreading.
What you should see
The warm water glass turns dark within a minute, the tap water takes several minutes and the cold glass shows only a thin plume. Higher temperature gives faster diffusion.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01What is diffusion?
The spreading of particles from where they are many to where they are few.
02Why does heat speed it up?
The particles move faster.
03Why must we not stir?
Stirring mixes by force and hides the diffusion.
04Where else do you see diffusion?
Smell of food spreading through a house.
Take it further
Repeat with a drop of ink or food colour and a spoon of sugar, and compare dissolving rates.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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