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Activity

Chromatography with coloured marker pens

Summary: 
Students separate the colours in pen ink using chromatography.
Science content (2016 curriculum): 
Chemistry: Physical Changes, Solutions, Mixtures and Separating (2, 4, 5, 6)
Science topic (2005 curriculum connection): 
Physical Science: Properties of Objects and Materials (grade K)
Physical Science: Properties of Matter (grade 2)
Physical Science: Chemistry (grade 7)
Materials: 
  • container e.g. large yogurt tub
  • water to fill pot to a depth of about 1cm
  • white coffee filter, cut into strips (use a template for students to make them the correct length for the pot)
  • coffee stirrer sticks
  • small binder clips
  • water soluble pens
Procedure: 

Cut a strip of filter paper. For a class of students you will want to make a cardboard template of the correct length for students to trace around before cutting.
Make a line of pen colour near one end of the filter paper. (This line position can be on the template).
Clip the strip to the binder clip, slide onto the stick, then rest the stick over the pot. The end of the strip should dip in the water, but the coloured dot should be above the water level. (The template would be matched with the pot and water depth used.)
Allow the water to creep up the filter paper and separate the colours in the ink.
Remove the strip from the water before they run off the top, and lay the paper to dry.

Black, brown, blue, green colours usually work well. The darker colours are generally a mixture of more colours.

How does chromatography work?
The coloured dye molecules in the ink of the pen are attracted to both the water that it is in, but also the surface of the filter paper. Each different colour is attracted to the water or the filter paper to different extents. As the water moves up, the dye molecules that are most attracted to the water will move along fast with it. If the dye molecules are mostly attracted to the paper, they will get stuck to the paper and not move along with the water at all. Most colours are attracted to both the water and the paper, so will travel with the water for a while, then stick to the paper for a while. Depending on the relative attraction of a dye to the water and the paper, a colour will travel at its own rate. The differing rates of travel separate out the colours.

Chromatography can be used for separating mixtures of molecules in a solution. This technique is used a lot by chemists and forensic scientists.

By mixing the colours put on the filter paper, then cutting and mounting the best patterns, some great art work can be made.

Alternatively, students make dots of marker colour on filter paper pieces laid flat, then use the Q-tips to drip and smear drops of water over the colours to separate them.

Notes: 

Try the Exploratorium version: http://www.exploratorium.edu/science_explorer/black_magic.html

See the activity Chromatography with the ink pens (black) for a forensics use of the method to identify the pen that wrote a note

Grades tested: 
Gr K
Gr 1
Gr 2
Gr 3
Gr 4
Gr 5
Gr 6
Teacher: 
Brenda Koch
Donna Greening
Fiona Laporte
Gretchen Bartlett
Ingrid
Jane Kemp
Sonia Ko
Sonja Watson
Teaching site: 
Aboriginal Focus Elementary
General Gordon Elementary Science Club
ingridscience afterschool
Maple Grove Elementary
Laurier Elementary
Activity originally developed and delivered: 

Gordon Elementary Science Club