GCSE Combined Science (AQA)

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Chromatography

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Atomic structure and the periodic table A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes

Chromatography

5:47 Separation of Mixtures
Spec 4.1.1.2
Previous Fractional Distillation Next Development of the Atomic Model
  • Chromatography is used to separate mixtures of soluble substances.
  • It allows the separation of different substances dissolved in a solvent.
  • Chromatography is a physical process, not involving chemical reactions or creating new substances.
  • Example: Black ink can be separated into four colored pigments.
  • The process involves several steps:
  • Step 1: Draw a pencil line (baseline) near the bottom of filter paper.
  • Step 2: Add colored solutions as spots along the pencil line.
  • Step 3: Lower the paper into a solvent without submerging the pencil line.
  • Step 4: Dissolved substances move up the paper with the solvent.
  • Step 5: Results in a chromatogram showing spots for each dissolved substance.
  • Chromatograms help distinguish between pure and impure substances.
  • Pure substances show one spot on a chromatogram.
  • Impure substances show multiple spots, indicating different pigments.
  • Chromatograms can identify substances by comparing them with known substances.
  • Two substances are likely the same if their dots travel the same distance and are similar in color.
  • Example: Brown dye is likely a mixture of red, yellow, and blue dyes.
  • Further technical details about analyzing chromatograms are covered elsewhere in the course.

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