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Chromatography

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Chromatography is used as a means of separating mixtures. The word itself means ‘colour writing’. Chromatography can separate colours in order to see what colours make up that specific colour.

Chromatography experiment Materials:

  • Glass Jar
  • Glass rod
  • Filter paper
  • Scissors
  • Paper clip
  • Markers (different colours)
  • Pencil
  • Water

Method:

  • Cut the filter paper into a strip long enough to touch the bottom and top of the glass jar
  • With a pencil draw a horizontal line 2-3 cm from the bottom of the filter paper
  • Using your marker, draw a dot under the line you have just drawn
  • Pour 1 cm of your water (solvent) into the jar glass
  • Hang the paper into the jar (ensuring that the solvent is below the marker dot)
  • Place your rod over the top of the glass jar and wrap the remaining paper around it and secure it under the rod with a paper clip
  • When the water has reached the top of the paper, take it out of the jar and allow it to dry
  • Repeat the experiments using different coloured markers.

Question and answer

Q: How does this work?

A: The solvent (water) carries the multiple dyes in the ink dot up the paper.

Q: Why are some colours higher up on the paper than others?

A: If the dye is not very soluble, it comes out of the solution early therefore it appears at the bottom. If the dye is very soluble, it is carried by the water further up the paper.

Q: Does this experiment work on all paper?

A: No. The paper you use must be absorbent paper other examples include chromatography paper or paper from the side of a newspaper

Q: What if the dye is not water soluble?

A: If the dye is not water soluble, then you can use alternative solvents such as propanone, alcohol or hexane

What is paper chromatography used for?

  1. Forensic science: Forensic scientists can use chromatography in order to separate substances in a crime scene
  2. Art: Artists use chromatography to identify the breakdown of colours in order for them to remake the colours they need
  3. Food Colourings: food scientists can check that food companies are only using the appropriate food colourings