This question is about paper chromatography - AQA - GCSE Chemistry - Question 3 - 2021 - Paper 2

To determine the Rf value for the dye in the food coloring, follow these steps:

1. Prepare the Chromatography Paper:

   • Draw a pencil line near the bottom of the chromatography paper.
   • Place a small spot of the food coloring on this line.

2. Set Up the Beaker:

   • Fill a beaker with a suitable solvent (e.g., water or alcohol).
   • Ensure the solvent level is below the pencil line on the chromatography paper.

3. Assemble the Apparatus:

   • Place the chromatography paper into the beaker, ensuring it stands upright and the dye spot is above the solvent level.

4. Allow the Solvent to Travel:

   • Cover the beaker with a lid to prevent evaporation.
   • Wait for the solvent to travel up the chromatography paper until it nearly reaches the top.

5. Mark the Solvent Front:

   • Once the solvent has traveled, mark the highest point it has reached on the paper (the solvent front).

6. Dry the Paper:

   • Remove the paper from the beaker and allow it to dry.

7. Measure Distances:

   • Measure the distance from the start line to the center of the dye spot.
   • Measure the distance from the start line to the solvent front.

8. Calculate Rf Value:

   • Use the formula (R_f = \dfrac{\text{distance moved by substance}}{\text{distance moved by solvent}}) to determine the Rf value.