Final answer:
The questions address common practices in analytical chemistry, specifically chromatography and gel electrophoresis, focusing on the rationale behind certain procedures and the interpretation of results. The importance of preventing contamination and ensuring accurate results is emphasized.
Step-by-step explanation:
The questions posed seem to relate to techniques used in analytical chemistry, such as chromatography and gel electrophoresis, which are utilized for separating and analyzing compounds. Chromatography involves the separation of compounds based on their movement through a stationary phase, while gel electrophoresis separates molecules based on their charge and size under an electric field.
- A pencil is used to mark the paper in chromatography because ink from a pen may dissolve and interfere with the compounds being separated, potentially contaminating the sample.
- Each sample requires a different capillary tube to prevent cross-contamination between samples, which could lead to inaccurate results.
- In amino acid chromatography, not touching the paper is important because oils and contaminants from the skin can interfere with the separation process and result in unclear or inaccurate chromatograms.
- Identical Rf values do not necessarily indicate identical molecules, as different compounds can travel the same distance under certain conditions; structural differences and other factors can cause similar Rf values.
As for the ranking of chromatograms based on separation and the answers to analytical calculations such as retention times, capacity factors, and selectivity factors, these would be determined by the actual data from the chromatograms, which is not provided here. Therefore, these calculations cannot be performed without the specific data.