Chemistry · May / June 2023 · Paper 11 · Question 39

A paper chromatography experiment is used to find an $R_f$ value for Fe$^{3+}$(aq). The chromatogram is shown. [chromatogram diagram with solvent front, starting line, distances y and x, and Fe$^{3+}$ spot] To make the spot containing Fe$^{3+}$(aq) more visible, the paper is sprayed with aqueous sodium hydroxide so that a precipitate of iron(III) hydroxide forms. In the chromatogram, the $R_f$ of Fe$^{3+}$(aq) is given by ......1...... and the colour of the precipitate is ......2...... . Which row correctly completes gaps 1 and 2?

1. Agap 1: $\frac{x}{y}$, gap 2: red-brown
2. Bgap 1: $\frac{x}{y}$, gap 2: green
3. Cgap 1: $\frac{y}{x}$, gap 2: red-brown
4. Dgap 1: $\frac{y}{x}$, gap 2: green

As printed in the paper