What it shows
Coloured sweets often use a mix of dyes, and water carrying them up paper moves different dyes at different speeds. You split the colours of several sweets and learn how to separate a mixture without any chemicals.
The science
Water climbs the paper by capillary action and carries the dyes along. Dyes that dissolve well in water and cling little to the paper travel farther, while sticky ones stay near the start. This separation of a mixture on paper is called chromatography.
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.
- Colourful sugar-coated sweets (gems or candy balls), 5 colours
- Coffee filter or blotting paper, 4 strips
- A tall glass or jar
- Water and a pinch of salt
- A pencil and a ruler
- A dropper
- Tape to fix the strip
Safety
For this project: Do not eat the sweets used in the test and wash your hands. If anyone is allergic to food dyes, an adult handles the sweets.
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.
Draw a pencil line 2 cm from the bottom of the filter paper, and put a small dot on it for each candy colour.
Wet each sweet slightly with a drop of water and touch the dye to its own spot on the line.
Pour about 1 cm of water, with a pinch of salt, in the glass; the water level must stay below the pencil line.
Tape the top of the strip to a pencil laid across the mouth of the glass so the strip hangs straight with its tip just in the water.
Wait until the water climbs to near the top, then take out the paper and let it dry.
Mark how far each coloured band travelled and measure it in millimetres.
Compare the colours between sweets and note which ones show more than one dye.
What you should see
Some sweets produce a single band while others split into two or three dye bands, which shows that they are mixtures. The pattern is like a fingerprint of each colour.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01What does chromatography separate?
The substances in a mixture, using their different speeds in a moving liquid.
02Why must the pencil line be above the water?
So the dyes do not dissolve straight into the dish.
03What makes the water rise?
Capillary action in the paper fibres.
04Why use pencil, not pen?
Pen ink would also run and spoil the test.
Take it further
Compare a green sweet to a mix of blue and yellow and see whether they match.
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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