Simulation of Paper chromatography
Simulation description
This is a 3D paper chromatography simulation for the AQA GCSE Chemistry required practical on separating coloured substances and calculating Rf values.
Pupils work through four guided steps. They begin by choosing an ink sample from four options: black ink, green ink, purple ink, or brown food dye. They then set up the chromatography paper, which appears with a pencil baseline drawn 1 cm from the bottom and a spot of the chosen ink placed on it. Next they lower the paper into a beaker of solvent (by dragging, or via a single button in no-drag mode), with the solvent surface deliberately sitting below the baseline so the spot isn’t washed off. The solvent then rises up the paper by capillary action, carrying the different coloured components to different heights, and pupils watch the ink separate into distinct spots in real time. Finally the results card measures the distances and works out the Rf value for each colour.
A live card on screen shows the solvent front rising in centimetres and a progress bar, mirroring what pupils would actually measure in the lab. Optional labelled measurement lines mark the baseline and solvent front on the paper. The results screen presents a table of each colour’s distance moved, the solvent distance, and its Rf, plus a worked example, an explanation of why more soluble substances travel further, and the reminder that Rf is always between 0 and 1 with no units. Pupils can then rerun with a different ink to compare.
Each ink is modelled as a genuine mixture (black separates into three dyes, for instance), so the core idea lands: a pure substance gives one spot, a mixture gives several, and Rf identifies each. The full ClassAdapt Adapt accessibility suite is available throughout (theme, spacing, text size, colour-vision filters, reduce motion, no-drag mode, and more).
Suggested class activity
“Which dyes are in the ink?” — an Rf investigation (about 25–30 minutes)
Start by asking pupils to predict, before running anything, how many colours they think black ink is really made from. Most will say one, which sets up the surprise.
Have pupils run all four ink samples one at a time, recording in a results table for each: the number of spots seen, each colour, its distance moved, the solvent distance, and its calculated Rf. Ask them to complete the Rf calculation by hand for at least one colour before checking it against the simulation’s results card, so they’re practising the formula rather than just reading it off.
Then move to the reasoning questions: Which colour travelled furthest, and what does that tell you about its solubility and its attraction to the paper? Why must the baseline be drawn in pencil and not pen? Why does the solvent have to start below the baseline? Which inks share a component (for example, a yellow dye appears in several), and how can you tell?
Finish with a short discussion or exit question: “An unknown ink gives a spot with Rf = 0.60 in the same solvent. Looking at your table, which ink might it contain, and why is Rf more reliable than colour alone for identifying it?” This pushes them toward the key exam idea that Rf values, measured under the same conditions, are what actually identify a substance.
For stretch, ask pupils to sketch what a chromatogram of a pure dye would look like (a single spot) versus a mixture, and to explain why forensic scientists might use this technique.