What you need to make sweet rainbows
- Paint brush
- 2x 250 cm3 Beaker
- Two paper clips
- Chromatography paper
- Pack of assorted food colours
What to do
- Draw a pencil line 1 cm from the bottom of the chromatography paper.
- Use a clean paintbrush and clean water to remove the colour from a Smartie. Paint the colour in a small spot on to the line on the chromatography paper.
- Clean the brush and paint the colour of another Smartie on a small spot about 2 cm from the previous spot. Repeat this until all the colours are on the paper.
- Then repeat the process adding a drop of each food colouring with a clean paintbrush.
- Using the pencil write the name of each colour by the corresponding spot.
- Roll the paper into a cylinder, hold in place with paper clips. Put the cylinder in a beaker containing 1 cm of water. Allow the water to rise up the paper.
- When it reaches the top take the cylinder out of the water, carefully unroll it and examine it.
What you may notice
Smartie colours are made up of more than one colour!
The science behind it all
Chromatography allows us to separate complex mixtures into their individual components. As water is absorbed up the paper, it carries the components or colors with it. Some components of the food colouring travel farther than others, causing the different colors to spread out so you can see them.
Many dyes are also made up of multiple colors. You may even find that some of the ‘standard’ colours in the food colourings contain more than one colour. You should be able to compare the standard colours to those of the Smarties to discover which standard colours they contain.
Beyond the science
Chromatography can be used to separate far more complex mixtures than food colourings. It can be used to separate very complex mixtures with great precision. It can even be used to separate things that are very similar, for example proteins that vary by only a single amino acid. At the same time it can also be used to separate delicate items. In fact, chromatography can purify basically any soluble or volatile substance if you have the right equipment.