Chromatography
Chemistry: Cambridge International GCSE Supplement, topic 12.3.1
Chromatography
Chromatography is a process that separates a mixture into its different components.
2 phases
- Substances are picked up and carried by a mobile phase (liquid or gas).
- The mobile phase then moves through a stationary phase (solid or viscous liquid).
Separation of substances
- Depends on the distribution of a substance across the 2 phases:
- A substance moves far if it's more attracted to the mobile phase.
- A substance doesn't move far if it's more attracted to the stationary phase.
Strength of attraction
- Different components can sometimes be equally attracted to a solvent.
- Therefore, the number of spots a mixture produces can vary depending on the solvent used.
Locating agents
- Chromatography can also be used to separate colourless components in mixtures.
- Locating agents are used to show where the spots are.
- Locating agents bind with the components of the mixture and can form coloured products, which locate the compounds.
- In other cases, we can locate the spots under a UV lamp.
Test yourself on Chromatography
A substance in a mixture is much more strongly attracted to the stationary phase than the mobile phase during chromatography. How far would this substance travel up the paper?
How many chromatography spots are produced by pure samples, and why?