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P, Q, R and S are mixtures of food colourings - Edexcel - GCSE Chemistry Combined Science - Question 2 - 2016 - Paper 1
Question 2
P, Q, R and S are mixtures of food colourings. They are investigated using paper chromatography. Figure 4 shows the chromatogram at the end of the experiment. (i) W... show full transcript
Worked Solution & Example Answer:P, Q, R and S are mixtures of food colourings - Edexcel - GCSE Chemistry Combined Science - Question 2 - 2016 - Paper 1
Step 1
(i) Which mixture contains an insoluble food colouring?
Answer
To determine which mixture contains an insoluble food colouring, we observe the chromatogram shown in Figure 4. An insoluble coloring will not travel up the paper, appearing as a spot at the starting baseline. Upon examination of the options:
- Mixture P appears to have no movement, indicating it is likely insoluble.
- Mixture Q, R, and S show visible spots indicating solubility. Therefore, the answer is A: mixture P.
Step 2
(ii) Give a change that could be made to the experiment to obtain an Rf value for the insoluble colouring.
Answer
To obtain an Rf value for the insoluble colouring, the following change could be made: Use a solvent system capable of dissolving the insoluble dye or heat the paper chromatography setup to increase solubility. This would allow the dye to dissolve and move up the paper, enabling the calculation of its Rf value.