Lesson 19C.1

19C.1 Chromatography and Rf values Quiz: Pearson Edexcel Chemistry, Unit 19

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 19C.1, Chromatography and Rf values: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 19: Modern Analytical Techniques II, written with Revision Ninja.

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The 20 questions

  1. What is the Rf value if a spot travels 3.0 cm and the solvent front travels 6.0 cm?

    • 0.25
    • 2.0
    • 0.50
    • 3.0

  2. What is the stationary phase in paper chromatography?

    • The solvent that moves up the paper, carrying the dyes
    • The glass plate under the paper, which supports the sample
    • Water held in the cellulose fibres of the paper
    • The dye being separated, which is held by the paper

  3. What is the stationary phase in thin-layer chromatography on a silica plate?

    • A thin layer of silica gel
    • The solvent that rises up the plate
    • A layer of wax on the plate
    • A sheet of cellulose mixed with water

  4. Why is the origin line drawn in pencil rather than ink?

    • Ink would dissolve and run with the solvent, interfering with the separation
    • Pencil marks react with the solvent to form coloured spots that interfere with the reading
    • Ink gives a weaker reading of the Rf value, which makes the spots harder to measure
    • Pencil is cheaper than ink, so it is preferred for routine work in a school laboratory

  5. Why must the solvent level be below the origin line at the start of a chromatogram?

    • So that the paper absorbs more solvent
    • So that the sample does not dissolve into a pool of solvent at the base
    • So that the solvent evaporates before reaching the sample
    • So that the Rf value is larger than one

  6. A spot travels 4.2 cm and the solvent front travels 7.0 cm. What is the Rf value?

    • 0.60
    • 1.67
    • 0.42
    • 0.70

  7. A spot travels 2.5 cm and the solvent front travels 10.0 cm. What is the Rf value?

    • 0.75
    • 4.00
    • 0.25
    • 0.40

  8. A compound has the same Rf as a standard run under identical conditions. What can be concluded?

    • It is an isomer with a different molar mass
    • It must be a different compound, since Rf values never match
    • It may be the same compound, though this is not proof on its own
    • It is definitely the same compound, since Rf values are unique

  9. Which statement describes high performance liquid chromatography, HPLC?

    • A type of column chromatography in which a liquid solvent is pumped through the column at high pressure
    • A gas chromatography technique with a liquid mobile phase, which uses a column held at a fixed temperature
    • A thin-layer technique using a silica plate, in which the solvent rises up the plate by capillary action
    • A paper technique with a cellulose stationary phase, in which the sample is spotted onto the paper

  10. What is the mobile phase in gas chromatography, GC?

    • An inert carrier gas, such as helium or nitrogen
    • Water vapour from the injector
    • A liquid solvent such as ethanol
    • Silica gel that moves through the column

  11. In column chromatography, what causes different components to separate?

    • Different colours, which determine how fast each moves
    • Different densities, which control the flow rate of the mobile phase
    • Different melting temperatures, which decide which passes first
    • Different retention times, from different interactions with the stationary phase

  12. What is the advantage of combining GC with mass spectrometry, GC-MS?

    • MS separates the components, and GC then identifies them by colour
    • GC makes compounds more volatile so MS can weigh them
    • MS removes the carrier gas so GC can run faster
    • GC separates the components and MS identifies each one from its mass spectrum

  13. A longer retention time in gas chromatography most likely indicates what?

    • The component moves faster through the column, because it has a weaker link to the stationary phase
    • The component interacts more strongly with the stationary phase
    • The component is more soluble in the carrier gas, so it is carried more slowly through the column
    • The component has a lower boiling point, so it is less volatile and stays in the column longer

  14. Why does the choice of solvent affect the Rf value of a compound?

    • Solvents change the colour of the compound only, which in turn alters the position of the spot
    • Solvents change the molar mass of the compound, so the spot moves a different distance on the plate
    • Solvents remove the stationary phase from the plate, so the spot moves freely up the paper surface
    • Different solvents change how strongly the compound partitions between the mobile and stationary phases

  15. Two spots lie 1.5 cm and 3.0 cm from the origin, and the solvent front is at 6.0 cm. Which spot has the greater affinity for the mobile phase?

    • The spot at 1.5 cm, which has the greater molar mass only
    • The spot at 3.0 cm, which has the higher Rf of 0.50
    • The spot at 1.5 cm, which has the higher Rf of 0.50
    • Both spots have equal affinity, since they use the same solvent

  16. A spot moves 3.6 cm and the solvent front moves 8.0 cm. What is the Rf value?

    • 0.55
    • 2.22
    • 0.36
    • 0.45

  17. Two GC peaks have retention times of 4.2 and 6.8 min under identical conditions. Which statement is correct?

    • The second component has a lower boiling point
    • The second component is retained longer on the column
    • Both components elute at the same time
    • The first component is retained longer on the column

  18. Why must Rf values be reported together with the solvent and stationary phase used?

    • Rf depends on conditions, so comparison needs identical solvent and stationary phase
    • Rf values depend only on the size of the spot on the plate, which is why spots must be kept small
    • Rf values are constant for every compound regardless of conditions, so they can always be compared directly
    • Rf values are always larger than one for pure substances, so a value below one indicates an impurity

  19. What does an Rf value of 1.0 mean?

    • The compound is the same substance as the solvent, so the spot and the solvent front coincide exactly
    • The compound did not move from the origin, so it has a very strong attraction for the solvent
    • The compound moved with the solvent front, so it has no affinity for the stationary phase
    • The compound was decomposed by the solvent during the run, so the spot shows only the breakdown product

  20. What does an Rf value of 0 indicate?

    • The compound stayed on the origin, so it is held strongly by the stationary phase
    • The compound evaporated during the run, so no spot was left on the plate for measurement
    • The compound has the same Rf as the solvent, so it is carried up the plate with the mobile phase
    • The compound moved with the solvent front, so it has no attraction for the stationary phase at all

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