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Spectroscopy and Chromatography

Paper and thin-layer chromatography

  • 3 things to know
  • Unit A2 2

Overview

Two phases in paper chromatography, two phases in thin-layer chromatography and two-way chromatography.

What you need to know

Answer each one before you reveal it.

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Key term

On what principle does all chromatography separate a mixture?

Key term

What are the two phases in paper chromatography?

Key term

What are the two phases in thin-layer chromatography?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    On what principle does all chromatography separate a mixture?

    Model answer

    The components distribute themselves differently between a stationary phase and a mobile phase, so each travels at its own rate.

  2. 2

    What are the two phases in paper chromatography?

    Model answer

    The water held in the fibres of the paper is the stationary phase, and the solvent moving through it is the mobile phase.

  3. 3

    What are the two phases in thin-layer chromatography?

    Model answer

    A thin layer of silica or alumina on a plate is the stationary phase, and the solvent rising through it is the mobile phase.

  4. 4

    Why is the base line drawn in pencil?

    Model answer

    Ink would dissolve in the solvent and travel up the plate with the sample.

  5. 5

    Why must the base line start above the level of the solvent?

    Model answer

    If the spots were below the surface they would dissolve into the solvent in the tank rather than move up the plate.

  6. 6

    Why is the tank covered during a run?

    Model answer

    To keep the atmosphere inside saturated with solvent vapour, so the solvent does not evaporate from the plate and distort the separation.

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