Paper Chromatography and the Rf Value · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Split the ink, read the spots

Science · Matter & Materials · ages 14-15
Name ______________________   Date ____________

  1. Drawing the baseline in pen is fine because pen stays put.

    Circle one:   True   False

  2. What separates the dyes on the paper?

    • Each dye splits its time between paper and solvent differently
    • The paper shakes the dyes apart
    • Heavier dyes sink to the bottom

  3. A spot centre sits 3 cm above the baseline. The solvent front sits 10 cm above it. What is the Rf value?

    Answer: ______________

  4. Why must spots start above the solvent level?

    • So they wash off faster
    • So the run finishes sooner
    • So the sample does not dissolve off in one blob

  5. A strip shows two well separated spots. What is the sample?

    • A pure substance
    • A mixture of at least two substances
    • Pure solvent

  6. An unknown pen matches a known one only when what holds?

    • Every spot lines up with the same Rf values on the same run
    • Both pens cost the same
    • Both strips are the same size

  7. A dye barely moves in water but sprints in a saltier mix. What does that show?

    • Water is useless for all dyes
    • The dye changed colour
    • Solubility drives the race, so analysts tune the solvent

  8. Tom dips the paper so the solvent covers his spots. The result is one smeared blob. What went wrong?

    • He used pencil instead of pen
    • The solvent washed the sample off before the race began
    • He marked the front too early
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Split the ink, read the spots W1-mt_BAcCcz11ls-s1

  1. False · Pen ink dissolves and joins the race. Use pencil.
  2. Each dye splits its time between paper and solvent differently · Different splits between paper and liquid give different climbing speeds.
  3. 0.3 · Divide spot distance by front distance: 3 divided by 10 is 0.3.
  4. So the sample does not dissolve off in one blob · Dunked spots wash off before the race begins.
  5. A mixture of at least two substances · Each spot is one substance, so two spots mean a mixture.
  6. Every spot lines up with the same Rf values on the same run · Shared conditions plus matching spots make the match real.
  7. Solubility drives the race, so analysts tune the solvent · The method is tunable: pick the solvent that splits your pair.
  8. The solvent washed the sample off before the race began · Spots must start above the solvent or they never get to race.
Worksheet · LightMySky