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P, Q, R and S are mixtures of food colourings - Edexcel - GCSE Chemistry - Question 3 - 2016 - Paper 1
Question 3
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 - Question 3 - 2016 - Paper 1
Step 1
Which mixture contains an insoluble food colouring?
Answer
To determine which mixture contains an insoluble food colouring, we refer to the chromatogram in Figure 4. An insoluble food colouring will not move up the paper and will appear as a spot at the baseline. Observing the chromatogram, it is clear that mixture P has spots at the baseline while the others have separated. Therefore, the answer is:
A mixture P.
Step 2
Give a change that could be made to the experiment to obtain an Rf value for the insoluble colouring.
Answer
To measure an Rf value for the insoluble food colouring, we could modify the experimental setup by selecting a different solvent that may dissolve the insoluble colourant, allowing it to travel up the paper. Alternatively, we could physically remove the insoluble colourant from the baseline and find its position in the solvent front.
Step 3
Explain, by referring to Figure 4, which mixture is separated into the greatest number of soluble food colourings by this chromatography experiment.
Answer
In Figure 4, mixture Q displays the greatest number of distinct spots separated from each other, indicating multiple soluble food colourings. This separation occurs because each dye travels different distances on the chromatography paper based on its solubility in the solvent. Mixture Q, having the most spots, signifies that it contains various soluble colourings, while other mixtures have fewer spots.