Chromatography & Rf Lab

Chromatography & Rf Lab is a 3D analytical chemistry simulation of paper and thin-layer chromatography (TLC). A cellulose strip spotted with a mixture along its pencil baseline hangs inside a sealed glass developing chamber with its bottom edge dipped in a mobile-phase solvent pool. As capillary action draws the solvent front upward (ds), mixture components partition differently between the polar stationary paper and the rising mobile solvent, separating into distinct coloured bands (dx). Students can switch between Spinach Leaf Pigments, Black Marker Ink, and Food Dyes, tune solvent polarity, click any separated spot, and drag a 3D graduated centimeter ruler next to the chromatogram to verify Rf = dx / ds.

• Select Leaf Pigments and click each of the four separated spots from bottom to top: Chlorophyll b, Chlorophyll a, Xanthophyll, and Beta-Carotene.
• Drag the yellow 3D centimeter ruler next to the paper strip so its 0 cm mark aligns with the pencil Baseline, then read dx and ds to verify Rf = dx / ds.
• Change Elution progress from 30% to 95% and confirm that while both dx and ds grow as the solvent rises, their ratio Rf stays constant.
• Adjust the Solvent polarity slider and observe how polar pigments shift their migration distance relative to the non-polar carotene spot.
• Switch Mixture type to Black Marker Ink or Food Dyes to identify which dye component is most soluble in the mobile phase.

1. 1Calculate the retention factor Rf = dx / ds from the distance traveled by a solute spot (dx) and the solvent front (ds).
2. 2Explain how chromatography separates molecules based on competition between adsorption to the stationary phase and solubility in the mobile phase.
3. 3Explain why the baseline origin line on a chromatography strip must be drawn in pencil (graphite) rather than ink.
4. 4Predict why Rf values stay constant for a given compound, stationary phase, and solvent system regardless of how far the solvent front runs.

Questions teachers ask