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.

Skill development

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.

Learning objectives

  • 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.

Concepts supported

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.

Equipment

  • Filter paper (eg a coffee filter)
  • Plastic or paper bowl
  • Black felt tip pen
  • Cup of cold tap water

Procedure

  1. Draw a few spots on the filter paper
  2. Rest the filter paper on the bowl to catch any drips
  3. Dip your finger in the water to get a drop on the end and let it fall onto the spots
  4. 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.

Practical considerations

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.