Q5 V1 A student used paper chromatography to separate two components, I and II, in a solution. A spot of the solution was initially placed at the origin. The following results were obtained. [table]
| Distance Solvent front | 8.0 cm Component I | 4.0 cm Component II | 1.0 cm behind Component I
[/table] The Rf value of Component II is closest to

Question

BlackTom AI · Accepted Answer

To approach this chromatography question, let’s first restate what is being asked and list the given options clearly.
Question restated: In paper chromatography, the solvent front traveled 8.0 cm. Component I moved 4.0 cm from the origin. Component II is stated to be 1.0 cm behind Component I. The Rf value of Component II is asked for, choosing from the given options: a) 0.13, b) 0.38, c) 0.25, d) 0.68.
Now, evaluate each option one by one.
Option a (0.13): This value would imply a very small ratio of distance traveled by II to the solvent front. Since the solvent front is at 8.0 cm, 0.13 corresponds to a distance of about 1.04 cm (0.13 × 8.0). That is far less than the position described for II (which is either 4.0 cm or 3.0 cm from origin depending on interpretation). Therefore, 0.13 cannot be correct for II’s Rf.
Option b (0.38): If Component II is 1.0 cm behind Component I, and Component I is at 4.0 cm, then II’s distance from the origin is 3.0 cm. The Rf value is distance II traveled divided by the solvent front distance: 3.0 cm / 8.0 cm = 0.375, which rounds to 0.38. This matches the option closely, making it a plausible and correct value.
Option c (0.25): An Rf of 0.25 would correspond to a distance traveled by II of 2.0 cm (0.25 × 8.0). That would place II either at 2.0 cm from the origin, which contradicts the stated position (3.0 cm or 4.0 cm), so this option is inconsistent with the given data.
Option d (0.68): An Rf of 0.68 would imply II moved about 5.44 cm from the origin (0.68 × 8.0). This is far from the described positions (3.0–4.0 cm), so this value is not supported by the measurements provided.
Putting the pieces together, the only value that aligns with II being 1.0 cm behind I (and I at 4.0 cm) while the solvent front is at 8.0 cm is Rf = 3.0 / 8.0 = 0.375, which is approximately 0.38. The other options fail to match the distances implied by the data or misinterpret the relative positions.
In summary, option b is the value that best corresponds to the described scenario, while the remaining choices are inconsistent with the measured distances and the definition of Rf (distance traveled by component divided by distance traveled by solvent front).

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