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Chromatography with food colors

A lot of substances, we use every day are mixtures. Sometime we want to find out what is in a mixture or a given substance is mixture or not. There are a lot of methods to find, how many compounds present in a substance. One of the method is Chromatography. Chromatography is derived from the Greek words “Chromo=Color and gram=bands”. As the name suggests, this method separates the mixture by formation of colored bands. This method works only if the mixture is made up of colored components. If the components of the mixture is colorless, then this method won’t work. There are different methods of doing Chromatography. The method we are going to use here is paper Chromatography. And the mixture we are going to use is food colors or ink mixture (try red and blue).

Things needed:
  • Chromatography paper or filter paper
  • Food colors or ink mixture
  • Pencil
  • Beakers
  • Capillary tube
Experiment:
  1. Take a filter paper and cut it into 1 X 6 inch rectangular strips or use a Chromatography paper. Draw a horizontal line 4 cm form one end of the paper using pencil.
  2. Using a fine capillary tube, put a drop of the mixture in the middle of the line. Let it dry. Again put a drop on the same spot and let it dry. Do this 5 or 6 times. More repetition is necessary if the mixture has weak concentration.
  3. Tape the strip to a pencil and let the pencil sit across the beaker, the strip will hand down into the beaker.
  4. Pour water into the beaker until it barely touches the bottom of the strip. Note that the mixture should not touch the water.
  5. Leave the strip hanging in the water until the water wets the top of the strip. After the water reaches the top, take it out and let it dry.
Observation:

As the water rises up the paper, it carries the components of the mixture with it. Some components will travel faster than the other, causing the different colors to spread out.

How many colors do you see?

Try the experiment mixing two or more food color or ink.

Try this:

You can do this experiment with permanent marker or highlighter (non primary colors). Just put a dot using the marker or highlighter on the pencil line instead of food color. Since the marker/highlighter pigment won’t dissolve in water, you have to use Iso propyl (rubbing) alcohol, instead of water in the beaker.