Chemistry
Chemistry
Problem
A student spots two dyes at the origin of a cellulose paper chromatogram and develops the plate in a 1-propanol/water solvent system. Dye X contains multiple –OH and –NH₂ groups, whereas Dye Y consists largely of non-polar hydrocarbon chains. Which statement best predicts their relative Rf values? a) Dye X will have a larger Rf because its polar groups increase solubility in the polar mobile phase and allow it to move farther. b) Dye Y will have a larger Rf because it interacts weakly with the polar stationary phase and travels farther with the solvent front. c) Dye Y will have a smaller Rf because its non-polar chains are poorly soluble in the propanol/water solvent and therefore remain near the origin. d) Dye X and Dye Y will have identical Rf values because both experience hydrogen bonding to the solvent and the paper.Intuitive explanation
The key to chromatography is understanding polarity matching: dyes that are more similar in polarity to the mobile phase travel farther, while those that interact strongly with the stationary phase stay closer to the origin. Since 1-propanol/water is a polar solvent system, the non-polar Dye Y will dissolve readily in it and move with the solvent front, whereas Dye X's many hydrogen-bonding groups will stick to the polar cellulose paper through intermolecular attractions. This means Dye Y will have the higher value—the core insight is that like dissolves like.
Intuitive explanation
The key to chromatography is understanding polarity matching: dyes that are more similar in polarity to the mobile phase travel farther, while those that interact strongly with the stationary phase stay closer to the origin. Since 1-propanol/water is a polar solvent system, the non-polar Dye Y will dissolve readily in it and move with the solvent front, whereas Dye X's many hydrogen-bonding groups will stick to the polar cellulose paper through intermolecular attractions. This means Dye Y will have the higher value—the core insight is that like dissolves like.