Thin-Layer Chromatography (Cambridge (CIE) A Level Chemistry): Flashcards

A stationary phase is a polar solid coating (typically silica or alumina) on a metal sheet, to which solute molecules adsorb and across which they are separated.

The solvent front is the furthest point the mobile phase travels up the plate. The baseline must be above the solvent level so the sample spot dissolves in the mobile phase rather than washing directly into it.

The R_f value is calculated as the distance travelled by the component divided by the distance travelled by the solvent.

False. More polar components have lower R_f values because they are more strongly attracted to the polar stationary phase and travel shorter distances.

Pencil is inert and does not react with the sample components or the solvent. Ink would dissolve in the mobile phase and interfere with the separation.

An R_f value is the ratio of the distance travelled by a component to the distance travelled by the solvent front in chromatography, used to identify substances by comparison with reference data.

Uncoloured components can be identified by viewing the plate under UV light or by treating it with ninhydrin, which reacts with certain compounds (e.g. amino acids) to produce coloured spots.

False. A less polar mobile phase is less effective at carrying polar components, so they remain closer to the baseline. A more polar mobile phase increases the R_f of polar substances.

In TLC, component separation depends on the solubility of each component in the mobile phase and its interaction with the stationary phase.