Question

The correct statements among the following, for a "chromatography" purification method is:

• A. Organic compounds run faster than solvent in the thin layer chromatographic plate.
• B. Non-polar compounds are retained at top and polar compounds come down in column chromatography.
• C. Rf of a polar compound is smaller than that of a non-polar compound.
• D. Rf is an integral value.

Answer 1

The Correct Option is C

To solve this question, we need to evaluate the statements regarding the chromatography purification method and determine the correct one among them.

Let's analyze each given statement:

• Statement 1: Organic compounds run faster than solvent in the thin layer chromatographic plate.
  In thin layer chromatography (TLC), compounds move up the plate based on their affinity to the stationary phase and their solubility in the mobile phase. Organic compounds do not inherently move faster than the solvent; rather, it depends on their interaction with the phases. This statement is generally incorrect.
• Statement 2: Non-polar compounds are retained at top and polar compounds come down in column chromatography.
  In column chromatography, the stationary phase is usually polar (e.g., silica gel), while the mobile phase is non-polar. Non-polar compounds move faster through the column and elute first, while polar compounds are retained longer. This statement is incorrect as described.
• Statement 3: Rf of a polar compound is smaller than that of a non-polar compound.
  The retention factor (Rf) is the ratio of the distance traveled by the compound to the distance traveled by the solvent front. In TLC, polar compounds interact more strongly with the polar stationary phase and thus travel less than non-polar compounds. Therefore, this statement is correct.
• Statement 4: Rf is an integral value.
  The Rf value is a ratio and is typically a decimal between 0 and 1, not an integral value. This makes the statement incorrect.

Therefore, the correct statement among the given options is "Rf of a polar compound is smaller than that of a non-polar compound."

Answer 2

Non-polar compounds have a higher value of R_f than polar compounds in chromatography.
Thus the correct answer is Option 3.