New draft Experiences and Outcomes within Materials - Forensic Science 

CSI:Primary - Forensic Science       Activity challenge   
 Experiment

Draft Outcome

I can use my knowledge on separation techniques to solve problems or challenges in a scientific way.   SCN 234AA  

 CSI:Primary - Forensic Science

Activity Challenge - In a crime scene scenario, examples of which can be found online, a written message was left, and when the suspects were searched, each one was found to have a black pen. These pens were all different so this gives us a chance to match up the ink in the pen with the ink left in the message.

Paper chromatography can be used to  investigate the inks. Black ink often contains other colours too. We need to try and separate the colours in our inks.

Experiment

Cut 5 squares from the kitchen roll (about 8 cm square)

Label each piece of paper in a corner using a biro or permanent marker – A, B, C, D and X

Use Pen A to make a dot of ink in the centre of the square of paper labelled A. Do the same for samples B, C and D. Try to make the dots about the same size. Put your papers on a tray and add two drops of water on to each of the ink spots.

Now we need to investigate the sample from the message.

Cut a small section of the message (about 3-4 mm). Try to just have black ink without too much white paper round it.

Take the X-marked square of kitchen roll paper and carefully put the sample with the black ink in the centre. Put it on the tray and add two drops of water as before.

The water will move out through the paper and will separate out any colours that might be in the ink.  Different colours will be carried for different distances through the fibres of the paper. Leave these samples to continue moving.

Most felt tip pens have washable ink. This means that the ink will dissolve in water and be carried along with the water moving through the fibres of the paper. However, the coloured inks will each have different chemicals in them and this will affect the rate at which they move. If you are using a pen with ink that is not washable, you will find that the ink dot does not spread out with water. These pens may say “permanent ink” or “non-washable ink”. You will notice that they smell different from the washable ones.

Look at your five sample papers.

Does sample X look the same as any of the others?

 Can any of the suspects be eliminated because their pen does not match?

It would appear that sample A and X are from the same pen.

Materials - Useful websites