O-Level Chemistry Chromatography & Distillation Diagnostics

TL;DR
Chromatography and distillation remain signature separation techniques in Paper 3, and SEAB expects candidates to justify solvent choices, apparatus setups, and fraction cuts.
Planning credit hinges on stating control variables (baseline height, condenser direction, heating rate), while MMO/PDO marks come from disciplined observation recording and diagrammatic support.
ACE answers should reconcile Rf trends, fraction purity, and error sources, then recommend refinements grounded in SEAB's apparatus expectations.

Continue the Separation Sprint

Pair these diagnostics with the rest of our O-Level Chemistry Experiments hub so every Paper 3 routine—from qualitative analysis to titration—has a matching rehearsal guide.

1 | Where separation appears in the syllabus

• SEAB lists separation techniques (e.g., paper chromatography, filtration, distillation) within the Paper 3 practical techniques and expects candidates to plan, observe, present data, and evaluate outcomes (SEAB syllabus).
• When writing plans, cite realistic school-lab apparatus from the syllabus’ apparatus/material guidance list (e.g., thermometers, measuring cylinders, tubing, and common glassware).

2 | Planning pointers for chromatography

1. Aim & reference. “Separate food dye components using paper chromatography and calculate Rf values.”
2. Control variables. Baseline height, solvent depth (below baseline), spot size/spacing, temperature, and solvent type.
3. Method outline.
   • Draw a pencil baseline ~1.5 cm from the bottom edge; mark origin points equally spaced.
   • Apply samples using capillary tubes, allowing spots to dry between applications.
   • Place the strip into a covered beaker containing solvent to just below the baseline; maintain a saturated atmosphere to prevent solvent evaporation.
   • Remove the strip once the solvent front is ~1 cm from the top, mark the front immediately, and dry the chromatogram.
4. Risk & safety. Note flammability or toxicity of organic solvents; recommend working in a ventilated area and wearing safety goggles.
5. Data usage. Plan to measure travel distances (mm) for each component and compute Rf values with significant figures matching the measurements.

3 | Planning for simple and fractional distillation

1. Aim. Example: “Separate ethanol from an ethanol–water mixture via fractional distillation.”