In this activity, students will explore chromatography, and solve a mystery.
Inks, paints, and dyes consist of particles of colour that are dissolved or suspended in a liquid base. When you write, the liquid part dries and leaves just the colour behind.
When the water creeps up filter paper on which a note has been written in felt marker, it contacts the dried colour. The colour molecules in the ink are dissolved and wicked up the strip with the water by capillary action. The more soluble a molecule is in water, the farther it will be carried by the water, higher up the paper.
Different colours are made of different sized molecules, that disolve differntly into water, some get carried further and faster than others. This process is called chromatography: the separation of a mixture by passing it in solution or suspension through a medium in which the components move at different rates.
In this activity: A mystery culprit has left behind a note and the students are asked to determine which of the 4 suspects wrote the note. Each suspect owns a different marker. Each brand of marker will have a different combination of pigments; by separating out these pigments and comparing them we can find out which pen was used to write the note.
Teacher Tip:Permanent marker and dry-erase board inks are not water soluble, so the water will not be able to dissolve its pigments to carry them up the strip. Be sure to use Washable felt pens with water soluble ink.