Chromatography Techniques (5C) Practice Test

A researcher purifies a small-molecule inhibitor from a crude reaction mixture using silica gel column chromatography (polar stationary phase). The mixture contains four neutral compounds at room temperature: hexane (H), ethyl acetate (EA), acetophenone (AP), and aniline (AN). The column is initially eluted with 100% hexane, then switched to 30% ethyl acetate in hexane (v/v) after 5 column volumes. No acid/base modifiers are used. Which component is expected to elute first under the initial 100% hexane mobile phase conditions?

Assume relative polarity increases in the order: H < EA < AP < AN, and that more polar compounds interact more strongly with silica.

A lab compares thin-layer chromatography (TLC) of a mixture of two analgesics on silica plates (polar stationary phase) using two different mobile phases. Spots are visualized under UV, and $R_f$ values are recorded.

Mobile phase 1: hexane:ethyl acetate = 8:2 (v/v)

Mobile phase 2: hexane:ethyl acetate = 2:8 (v/v)

Compound X is more polar than compound Y. Based on the setup, which outcome is most consistent with switching from mobile phase 1 to mobile phase 2?

Assume both compounds are neutral and remain chemically unchanged during development.