GCSE Chemistry Required Practical: Calculating Retention Factors

Key Stage 4

Meaning

Use a Chromatography experiment to produce a Chromatogram and calculate the Retention Factors (R_f) for they dyes found within different inks.

Method

1. Take a piece of chromatography paper of width 6cm and height 10cm.
2. Using a ruler draw a line with pencil across the width 2cm up from the end.
3. Add a dot of each unknown sample on the pencil line at 1cm intervals.
4. Suspend the chromatography paper in a suitable solvent just below the pencil line with most of the paper above the solvent.
5. Wait until the solvent stops rising up the paper.
6. Remove the paper from the solvent and draw a pencil line at the boundary between the dry and wet areas, then leave the paper to dry completely.
7. Use a ruler to measure the distance that the solvent has traveled up the paper.
8. Use a ruler to measure the distance that the different dyes have traveled up the paper.
9. Use the following equation to find the Retention Factor for each dye:

\[R_f = \frac{d_c}{d_s}\]

Where:

R_f = Retention Factor

d_c = distance moved by the chemical

d_s = distance moved by the solvent