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2024 O Level Chem P1 Q5 — Chromatography Solution

Chromatography 2024 O Level Pure Chemistry · Paper 1 · Q5

Question

Three samples of colourless compounds, X, Y and Z, are investigated using paper chromatography. The chromatogram obtained is shown. Which statement about the chromatography investigation is correct? Question diagram

Question diagram

AA locating agent is used in this investigation.
BSample X contains only one compound.
CThe chromatogram for sample Z may be used to investigate its % purity.
DThe Rᶠ value of one of the components in Y is half the Rᶠ value of one of the components in X.

Correct answer: A

Video Solution

Explanation

Answer: A. The samples are colourless. For their spots to appear on the chromatogram at all, a locating agent — UV light or a chemical spray such as ninhydrin — must be used to develop the spots. The chromatogram as shown therefore confirms a locating agent was applied.

B is wrong: a single spot for X tells us only that any components in X have the same \(R_f\) under these conditions. There may still be co-eluting compounds. C is wrong: chromatography shows separation, not absolute purity (a single spot isn't proof). D is wrong: the \(R_f\) ratios shown aren't necessarily a clean 1:2 between samples — read the diagram, not symmetry.

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