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Combined Science: Chemistry

GCSE · Edexcel · higher

QuestionsFlashcards

Group 1
- Group 1 (Alkali Metals)
  5
- Group 1: Reactivity & Electronic Configurations
  3
Group 7
Group 0

Interpreting Chromatograms Flashcards

All 6 cards in this deck

In paper chromatography, what are the mobile phase and the stationary phase?: Mobile phase = the solvent running through the paper; stationary phase = the paper.
Why do the substances in a mixture move different distances up chromatography paper?: They have different solubilities in the solvent, so they move at different rates over the paper.
What does a chromatogram show for a pure substance?: A single spot. An impure substance (mixture) gives two or more spots.
What is the formula for the $R_f$ value?: $R_f = \frac{\text{distance moved by the spot}}{\text{distance moved by the solvent front}}$
Rearranged: distance moved by spot $= R_f \times$ distance moved by solvent front.
A spot from a mixture has the same $R_f$ value as a known pure substance run in the same solvent. What does this suggest?: The mixture probably contains that substance.
In paper chromatography, which substance in a mixture ends up furthest up the paper?: The one that is most soluble in the solvent. It travels with the moving solvent for more of the time, so it gets furthest from the start line.