1. 1
   A food scientist places a small spot of a sports drink extract near the base of a strip of chromatography paper, dips the base in a solvent, and allows the solvent to rise up the paper.

   (a)

   Which part of the apparatus acts as the stationary phase during this separation?

   [1 mark]

   • AThe chromatography paper
   • BThe solvent
   • CThe pencil baseline
   • DThe beaker holding the solvent

   (b)

   In the same experiment, which substance acts as the mobile phase as the separation takes place?

   [1 mark]

   • AThe paper
   • BThe dye spot
   • CThe solvent
   • DThe pencil line

   (c)

   After the run, the scientist finds that the sports drink extract has separated into three distinct spots. Explain, in terms of relative solubility, why the components of the extract have moved different distances up the paper.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student runs an unknown ink sample alongside three reference dyes, X, Y and Z, on the same sheet of chromatography paper. After the solvent front has travelled 8 cm, the unknown ink produces two spots, one of which lines up at exactly the same height as reference dye Y.

   (a)

   What can the student conclude?

   [1 mark]

   • AThe ink is a pure substance identical to dye Y
   • BThe ink is a mixture that contains a substance with the same identity as dye Y
   • CThe ink cannot contain dye Y because two substances never travel the same distance
   • DThe ink and dye Y must have been dissolved in different solvents

   (b)

   The student notices that reference dye Z produces only a single spot when run on its own. What does this indicate about dye Z?

   [1 mark]

   • ADye Z is definitely a mixture of two substances
   • BDye Z reacted with the paper
   • CDye Z did not dissolve in the solvent
   • DDye Z is likely to be a single, pure substance

   (c)

   One spot from the unknown ink travels 5.6 cm from the baseline, while the solvent front travels 8.0 cm from the baseline. Calculate the Rf value of this spot, giving your answer to two decimal places, and state what an Rf value represents.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A forensic technician suspects a sample of green ink used to forge a signature is a mixture of dyes, not a single pure pigment. The technician plans to run paper chromatography using a non-aqueous solvent because the ink does not dissolve well in water.

   (a)

   Describe how the technician should set up and carry out the chromatography experiment to test the ink sample.

   [3 marks]

   (b)

   After running the chromatogram, the technician sees that the green ink has separated into a blue spot and a yellow spot at different heights, while a genuine reference sample of green ink produces only a single green spot. Explain what this result shows about the suspect ink, and suggest one improvement the technician could make to increase confidence in the identification.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A quality control team at a sweet manufacturer must determine whether a batch of red food colouring, recently received from a new supplier, is a single pure compound or a mixture of dyes, before it can be approved for use in sweets.

   (a)

   Describe, in detail, how the team could use paper chromatography to investigate the purity of the red food colouring, including how the results would be interpreted to reach a conclusion.

   [6 marks]

   (b)

   The team finds that the red food colouring separates into three spots. To identify the individual dyes, they decide to run the sample alongside five known reference dyes on the same chromatography paper, and to calculate Rf values for every spot. Evaluate this approach as a method of identifying the dyes present, discussing both its strengths and its limitations.

   [6 marks]

   Total for question 4: 12 marks

End of questions