Q6 V3Consider the following TLC plate of compounds X, Y and Z developed using a suitable mobile phase on a polar stationary phase. Which of the following is correct?

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Question restatement: The TLC plate shows three components X, Y and Z developed on a polar stationary phase with a suitable mobile phase. We must choose which statement is correct about their relative polarity and Rf values.

Option a: 'Z is more polar than X and has a higher Rf value than X.' On a polar stationary phase, more polar compounds interact more strongly with the stationary phase, which lowers their Rf (they travel less). If Z were more polar than X, Z would typically have a lower Rf, not a higher one. Additionally, claiming Z has a higher Rf than X contradicts the expected trend for a polar stationary phase. Therefore this statement is inconsistent with the usual TLC polarity behavior and is unlikely to be correct.

Option b: 'X is the most polar component and has an Rf value of 0.80.' If X were the most polar, it would interact most strongly with the stationary phase and would move the least, giving a relatively low Rf. An Rf of 0.80 suggests considerable movement up the plate, which would be unusual for the most polar compound on a polar stationary phase. This makes the statement questionable and likely incorrect.

Option c: 'Z is more polar than Y and has a higher Rf value than Y.' If Z were more polar than Y, Z should have a stronger interaction with the stationary phase and thus a lower Rf than Y. Claiming that Z has a higher Rf than Y contradicts the premise that Z is more polar. Therefore this option is inconsistent with the polarity–Rf relationship on a polar stationary phase and is not correct.

Option d: 'Y is the least polar component and has an Rf value of 0.78.' This aligns with the general principle: on a polar stationary phase, the least polar compound interacts least with the stationary phase and travels farther with the mobile phase, yielding a higher Rf. An Rf of 0.78 is a plausible value for a component that travels well up the plate but not to the solvent front, and labeling Y as the least polar fits the reported trend. This option is consistent with standard TLC behavior and matches the provided answer key.

Summary of reasoning: In TLC on a polar stationary phase, polarity inversely affects mobility: more polar compounds have lower Rf due to stronger interaction with the stationary phase, while less polar compounds move farther and have higher Rf values. Applying this to the options, only statement d coherently matches the expected polarity–Rf relationship and the given hint that Y is least polar with a relatively high Rf (0.78).

MUF0042 Chemistry Unit 2 - Semester 2, 2025

Q6 V3Consider the following TLC plate of compounds X, Y and Z developed using a suitable mobile phase on a polar stationary phase. Which of the following is correct?

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