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.

Downloads

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Additional information

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.