by Nirvan Garg, 11

Apparatus:

• A strip of porous paper (such as kitchen towel)
• A pencil and ruler
• A brush pen or marker
• Water
• A cylindrical container to hold the water

Procedure:

1. Fill the bottom of the container with a small amount of water. It should be quite shallow and not very deep.
2. Take the paper, and draw a line through the centre lengthwise using the ruler. After this, draw another line, perpendicular to the first, parallel to the width, but make sure that this line is towards the bottom of the paper. However, it should not be very close to the edge.
3. Take the brush pen or marker and draw a singular dot at the place where both lines intersect.
4. Tape the other end of the paper, away from the dot, to a pencil.
5. Lower the paper strip into the container, ensuring that the paper touches the water, BUT THE INK DOT DOES NOT. The pencil acts as a stopper, ensuring that the paper does not fall into the water.
6. Leave for at least two hours. When you return, you should see different colours, at different heights along the paper.

Explanation:

Chromatography is a method to separate mixtures. The idea is that in a mixture, each constituent has a different solubility in the solvent (in this case water). The ink of the brush pen/marker is a mixture of multiple dyes. As each dye has a different solubility, it dissolves in the water and travels up the paper at a different rate, and we can see the constituents separated.