After hexane is removed from a mixture of two organic dyes by evaporation
CHEMISTRY · Single correct · A Level · Chemistry · Chromatography · Chromatography
Problem
After hexane is removed from a mixture of two organic dyes by evaporation, the residue is analyzed by thin-layer chromatography (TLC) on polar silica gel using a moderately polar solvent system. The more polar dye is observed to travel a significantly shorter distance than the less polar dye. Which of the following statements BEST explains this observation?
(a) The more polar dye is less soluble in the moderately polar mobile phase, so it partitions less into the mobile phase and therefore moves a shorter distance.
(b) The more polar dye experiences stronger London dispersion forces with the mobile phase, so its upward migration is slowed.
(c) The more polar dye forms stronger dipole–dipole and hydrogen-bond interactions with the polar silica surface than with the mobile phase, so it is retained longer on the stationary phase.
(d) Because the more polar dye has a greater molar mass, its diffusion is slower, so it lags behind the less polar dye on the TLC plate.