Sometimes in science, one black can be as different to another black as most black is to white. Confused? You won’t be if you try the experiment below.
CHROMATOGRAPHY TEST
When a crime is committed sometimes a few chemicals might be left behind. For example, a patch of mud, a paint stain, or some ink. These chemicals can be analysed and sometimes matched to a suspect to potentially convict them of the crime.
Chromatography is just one process that can be used to analyse such chemicals. You needn’t look further than your home to find all the scientific equipment you need to try this chemical detective procedure.
WHAT YOU NEED:
• Filter paper (coffee filters work well)
• As many non-permanent felt tip pens as you can find.
• Plastic cups (you’ll need one more cup than the number of pens you have)
• Jug of water
WHAT YOU DO:
1. Cut the coffee filter paper into long strips about 3cm wide (with the grain of the paper running along the length of each strip, not across its width). You’ll need one more strip than the number of textas you have.
2. Use one of the textas to draw a tiny dot about 2cm from the end of one of the filter paper strips. Repeat for each texta (using a different piece of filter paper each time).
3. Ask a friend to use one of the pens to draw a tiny dot 2cm from one end of the final strip of filter paper. Don’t let them tell you which pen they’ve used. This is for them to know and you to find out! Label this final strip of paper with a question mark at the top.
4. Pour a little water into each plastic cup (enough to just cover the base of each cup).
5. Place each strip of filter paper into a different cup (placing the ink dot at the bottom). The paper should touch the water at the base.
6. Fold the top of the paper into a little ‘hook’ over the lip of the cup so it doesn’t fold up and fall into the cup. Place each texta next to the cup with its corresponding ‘ink sample’.
7. Watch as the water rises and the ink of each pen separates into a rainbow pattern of colours! Which pattern matches the pattern from the mystery ink dot?
CONCLUSIONS
As you’ve just learnt, black isn’t always black! Sometimes a rainbow of colour lurks beneath the inky darkness. The chemical technique you used to unlock these colours is called chromatography.
In our experiment (an example of ‘paper chromatography’) water rises through the filter paper carrying parts of the ink with it as it climbs. Most inks are made from a variety of different coloured inks. Each colour will dissolve differently in water. The colours that dissolve best get carried the highest on each piece of paper and those that don’t dissolve as well aren’t carried as high.
DID YOU KNOW?
Chromatography was initially developed as a way of separating coloured substances from plant leaves. The word literally means ‘colour writing’. The term now refers to processes used to separate both coloured and non-coloured substances.
Chromatography can be used to determine the components of many ‘mystery’ combinations of chemicals, including gases. The process can also be used to purify chemicals.
4. Pour a little water into each plastic cup (enough to just cover the base of each cup).