Inside many black pens is a rainbow of colour trying to get out. Black ink is often made from a blend of other colours
In this activity, learners can try out paper chromatography to separate this mixture of inks.
Children will develop their working scientifically skills by:
- Using appropriate scientific language and ideas to explain, evaluate and communicate their methods and findings.
- Drawing conclusions and raising further questions that could be investigated, based on their data and observations.
- Asking their own questions about scientific phenomena.
- Use knowledge of solids, liquids and gases to decide how mixtures might be separated.
- Compare and group together everyday materials on the basis of their properties, including their solubility.
Children will learn:
- That certain colours and dyes are made up from a mixture of colours, and these can be separated by using techniques such as chromatography.
- Filter paper (eg a coffee filter)
- Plastic or paper bowl
- Black felt tip pen
- Cup of cold tap water
- Draw a few spots on the filter paper
- Rest the filter paper on the bowl to catch any drips
- Dip your finger in the water to get a drop on the end and let it fall onto the spots
- Watch what happens to the ink – is the black ink really black?
What’s the chemistry?
Being able to separate mixtures is really useful. There are lots of different types of chromatography – from simple methods like this, to sophisticated machines like liquid chromatography–mass spectrometry (LC-MS) which can separate a mixture and measure the mass of the components all at the same time.
Suggested activity use
This activity could be used with a whole class, with learners working in small groups, investigating how to separate colours. They could start by investigating a black pen and could then move to look at different coloured pens and sweets, observing the results closely.
You may need to experiment with a range of black pens beforehand, as some pens work better than others.
Filter paper will be required as certain papers are not absorbent enough to separate the colours out effectively.
- Handout | PDF, Size 3.57 mb
- Handout | PDF, Size 0.32 mb
This activity was demonstrated by the RSC at the Big Bang Fair 2014, and is a featured resource in our autumn 2015 ‘Get colourful with chemistry’ theme.