(a)     State how you could tell whether the ink was a single substance or a mixture of components.

(b)     Explain how paper chromatography separates the components.

(c)     The \({R_{\text{f}}}\) value of the components of the ink could be measured. Define the term \({R_{\text{f}}}\).

(d)     State one factor that would alter the \({R_{\text{f}}}\) value of a particular component.

(a)     whether chromatogram had just one spot or number of spots / OWTTE;

Allow “component/dot / OWTTE” for spot.

(b)     different components have different attractions/affinities/bond strengths/solubilities for two phases / OWTTE;

components strongly absorbed/adsorbed by stationary phase move less / components weakly absorbed/adsorbed by stationary phase move more / components not very soluble in mobile phase move less / components very soluble in mobile phase move more / OWTTE;

(c)     distance travelled by component divided by distance travelled by solvent (front);

Allow spot/solute for component.

Accept R_f represented as an equation.

Do not allow just retention factor.

(d)     (nature of) solvent (used) / (type of) paper / temperature / pH;

Parts (a), (c) and (d) were well done. In (d) some candidates stated that solubility is a factor. However solubility depends on conditions and is not a factor per se. In (b) although often candidates stated that different components have different affinities for the two phases, some did not mention the two phases and others did not refer to comparative movement to score the second mark (e.g. components very soluble in the mobile phase will travel further / OWTTE). One G2 comment stated that the command term "explain" was not appropriate for this question. This was discussed at grade award and the senior examining team felt that this indeed was the most appropriate command term for the nature of the question asked.