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1CH0 · CP2.11Core practical investigationsCore

CP2.11: Ink Chromatography and Distillation

Use the approved paper, solvent and sample preparation. Place small sample spots on a pencil baseline above the initial solvent level. If a spot is submerged, the sample can dissolve directly into the reservoir rather than starting a controlled chromatographic separation. Pencil avoids introducing soluble ink from the baseline itself.

35 min Video by Pearson UK & International Schools Core practical investigations
Pearson Edexcel (9-1) GCSE Chemistry Core Practical - distillation and paper chromatographyCurated by Kepler, not produced by us. Watch it before the notes below.
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Before you start

  • Use your teacher’s tier checklist: this overview can include Higher-only material, and is not a tier-specific revision list.
  • Pearson Edexcel separate GCSE Chemistry 1CH0. Preserve the specification’s core-practical reference and any explicitly required subparts.
  • Distinguish a solute, a solvent, a mixture and a pure substance.
  • Use the centre’s approved supervised method, apparatus, heating and disposal arrangements. Written preparation does not replace performing and recording the practical activities.

Watch, pause, try

Video by Pearson UK & International Schools. The Pearson demonstration includes both ink-separation techniques. This core practical requires chromatography and simple distillation, with separate explanations of what each method achieves.

Viewing focus: Explain both required ink-separation methods

After watching, attempt these questions before opening the answers. You can also use the written lesson below.

After watching 1: Why do chromatography and distillation answer different separation questions?

Show answer and reasoning

Chromatography compares migration of detected components through the stationary/mobile system. Distillation recovers suitable volatile material through vaporisation and condensation.

After watching 2: How must distances be measured when calculating a chromatographic Rf?

Show answer and reasoning

Measure component and solvent-front distances from the same baseline, using matching units and a justified spot-centre rule.

What you'll be able to do

  • Explain both required ink-separation methods
  • Calculate Rf and a stated distillation recovery
  • Evaluate composition and purity claims from the two methods
1

Keep the sample above the initial solvent

Use the approved paper, solvent and sample preparation. Place small sample spots on a pencil baseline above the initial solvent level. If a spot is submerged, the sample can dissolve directly into the reservoir rather than starting a controlled chromatographic separation. Pencil avoids introducing soluble ink from the baseline itself.

The solvent moves through the paper, and components have different interactions with the moving solvent and stationary material. Different migration distances can separate a mixture. Use comparable conditions when placing reference samples alongside an unknown, and avoid overloading a spot so bands become difficult to distinguish.

A paper chromatogram has a common baseline, a solvent front 80 millimetres above it and a spot centre 25 millimetres above it. The example Rf is 25 divided by 80, about 0.313.
Scroll the diagram to see the full view.
Original measurement schematic. Read both distances from the baseline and use the spot centre. A reference at the same height supports a comparison, not a unique identity proof.
2

Measure from one origin

Mark the solvent front at the appropriate time before it becomes difficult to identify. Measure the component distance from the baseline to a justified spot centre and the solvent distance from that same baseline to the front. Distances from the bottom edge or from different origins cannot be combined into a valid Rf.

Rf = component distance ÷ solvent-front distance. Use the same units for both lengths; the ratio has no unit. A broad or streaked spot introduces positional uncertainty. Record the actual observations and measurement convention rather than selecting whichever edge produces an expected reference value.

3

Compare evidence under comparable conditions

An unknown component matching a reference spot under the same run conditions supports a possible identity. It does not uniquely prove identity because different substances can have similar migration. Rf depends on the chromatographic conditions, so comparisons across different solvents or papers need caution.

Several resolved spots support a mixture. One visible spot does not prove complete purity: components may overlap, fail to move or escape the detection method. Explain what was detected and propose a suitable further separation or detection comparison rather than treating one chromatogram as a universal chemical fingerprint.

4

Complete the second ink-separation method

Pearson CP2.11 includes simple distillation as well as paper chromatography. In an appropriate aqueous ink, a suitable volatile solvent can be vaporised and condensed while non-volatile dyes remain. The condenser removes energy from vapour; its cooling water is separate from the recovered distillate.

Follow the approved Bunsen-heating and apparatus method, with a correctly interpreted vapour path and receiver. Distillation recovers a suitable volatile component; chromatography separates detected components by their relative interactions. Explain which fraction contains the target after each method and why neither a clear liquid nor one visible spot is a universal purity proof.

A schematic simple-distillation apparatus shows a heated mixture, a thermometer bulb at the exiting vapour path, a sloping condenser with separate lower coolant inlet and upper outlet, and an open receiver collecting condensed distillate.
Scroll the diagram to see the full view.
Original schematic, not to scale or an assembly procedure. The gold path is heated vapour and the blue continuation represents collected condensate. Cooling water follows a separate jacket path, entering lower and leaving upper. The thermometer samples exiting vapour.
5

Worked applications

Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.

Example 1A spot centre is 25 mm above the baseline and the solvent front 80 mm above it. Find Rf.
1Use the common origin and matching units.
225/80 = 0.3125.
Answer
Rf ≈ 0.313, with no unit.
Example 2Two samples give one spot at the same height on one run. Is identical composition established?
1The spots show similar migration under those conditions.
2Different components can co-migrate or remain undetected.
Answer
No; the match supports a comparison but does not uniquely establish composition.
Example 3A suitable ink sample begins with 20.0 cm³ liquid and gives 12.5 cm³ collected distillate. Calculate volume recovery.
1Recovery = 12.5/20.0 × 100.
2This compares collected with starting liquid volume.
Answer
62.5% volume recovery, not 62.5% purity.

Common mistakes to avoid

Giving Rf a length unit.
It is a ratio of two lengths in matching units.
Measuring the component from a different origin to the solvent.
Use the baseline for both distances.

Key takeaways

  • You can explain both required ink-separation methods.
  • You can calculate Rf and a stated distillation recovery.
  • You can evaluate composition and purity claims from the two methods.

Apply it in an exam

Question 1: A suitable ink sample begins with 20.0 cm³ liquid and gives 12.5 cm³ collected distillate. Calculate volume recovery.

Show answer and reasoning

62.5% volume recovery, not 62.5% purity.

  • Recovery = 12.5/20.0 × 100.
  • This compares collected with starting liquid volume.

Explore further

Return to this tomorrow

Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.

  • Which distances define Rf?
  • Does a single visible spot prove complete purity?

Test yourself

Answer a few questions, then review anything you missed.

Next step

Keep practising

Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.

Browse practice topics

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