Final answer:
Both students suggest valid methods for using thin layer chromatography (TLC) to identify compounds by comparing the spots of unknown and known substances. Student 2 proposes separate TLC plates, while Student 3 recommends using the same TLC plate for direct comparisons, which can be more effective due to reduced variability in experimental conditions.
Step-by-step explanation:
When discussing how thin layer chromatography (TLC) could aid in the identification of a compound, the correct scientific reasoning is provided by both Student 2 and Student 3, with a slight preference for the method described by Student 3 due to convenience and direct comparison. In TLC, a baseline is applied where a drop of the solution containing the unknown compound is placed. A solvent then moves up the plate by capillary action, carrying the compounds at different rates, thus separating them.
The rational approach for identification involves comparing the unknown with known standards. TLC plates show compounds as spots, which can be visualized under UV light or by staining. The positions of these spots are represented by the retention factor (Rf), which is the ratio of the distance traveled by the compound to the distance traveled by the solvent. Comparing the Rf values and the pattern of spots provides information on the compound's identity.
Student 2 suggests using separate TLC plates to compare spots of unknown and known compounds, which is one valid method. However, running an unknown and a known compound side by side on the same plate, as suggested by Student 3, allows for more direct comparison, minimizing variables such as differences in TLC plate adsorbent, solvent composition, and environmental conditions.
Therefore, while both students use correct scientific reasoning, the technique proposed by Student 3 is more effective for direct comparison as it eliminates some possible variables that could affect the results.