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2023 O Level Chem P1 Q3 — Chromatography Solution

Chromatography 2023 O Level Pure Chemistry · Paper 1 · Q3

Question

Solution Y contains a mixture of flavourings. Solution Y and four other solutions, A, B, C and D, are analysed by chromatography. The result is shown in chromatogram 1. The chromatogram is then sprayed with a locating agent. This is shown as chromatogram 2. Which solution contains the same mixture of flavourings as solution Y? Question diagram

Question diagram

A
B
C
D

Correct answer: D

Video Solution

Explanation

Answer: D. Two solutions are the 'same mixture' only if their spots line up at the same \(R_f\) values in both chromatograms. Chromatogram 1 shows the coloured components only; chromatogram 2 (after the locating agent has been sprayed) reveals additional colourless components.

Solution Y has a specific set of spot heights in both chromatograms. Matching the complete pattern column-by-column against A, B, C, D: only solution D shows exactly the same combination of spots as Y at every \(R_f\) value across both chromatograms, with no extra spots and no missing spots.

Solutions A and B are missing spots that Y has (they share some components but not all). Solution C has a different combination of spot heights from Y — even if some spots happen to align, the full pattern doesn't match. Only D's full set of spots — visible in chromatogram 1 plus colourless ones revealed in chromatogram 2 — matches Y's full set.

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