Purity and separating mixtures

Medium

A forensic scientist analyzes a sample of black ink from a suspicious handwritten document using paper chromatography.

The black ink is compared to four reference inks: A, B, C, and D.

At the end of the experiment, the scientist records the following measurements:

Distance travelled by the solvent front: $\text{ cm}$
Distance travelled by ink A: $\text{ cm}$
Distance travelled by ink B: $\text{ cm}$
Distance travelled by ink C: $\text{ cm}$
The spots from the black ink sample are located at: $\text{ cm}$ and $\text{ cm}$

Answer the following questions:

The start line on the chromatography paper is drawn in pencil rather than ink. Explain why.

[2]

Reference ink D is insoluble in the solvent used. State where the spot for ink D will be located at the end of the experiment.

[1]

Use the recorded data to identify which of the reference inks (A, B, or C) is present in the black ink sample.

[1]

Calculate the $R_f$ value for ink B using the equation:

$solventR_f = \frac{\text{distance travelled by the substance}}{\text{distance travelled by the solvent}}$

Give your answer to 2 significant figures.

[2]

Purity and separating mixtures Questions