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Purity and separating mixtures

Purity and separating mixtures

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Question 19

A food scientist analyses a sample of green food coloring using paper chromatography.

The green food coloring is compared to four known dyes: P, Q, R, and S.

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

  • Distance travelled by the solvent front: 7.5 cm7.5 \text{ cm}7.5 cm
  • Distance travelled by dye P: 2.1 cm2.1 \text{ cm}2.1 cm
  • Distance travelled by dye Q: 4.7 cm4.7 \text{ cm}4.7 cm
  • Distance travelled by dye R: 6.2 cm6.2 \text{ cm}6.2 cm
  • The spots from the green food coloring sample are located at: 4.7 cm4.7 \text{ cm}4.7 cm and 3.2 cm3.2 \text{ cm}3.2 cm

Answer the following questions:

a.

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

[2]
b.

Dye S is insoluble in the solvent used. State where the spot for dye S will be located at the end of the experiment.

[1]
c.

Use the recorded data to identify which of the known dyes (P, Q, or R) is present in the green food coloring.

[1]
d.

Calculate the RfR_fRf​ value for dye Q using the equation:

Rf=distance travelled by the substancedistance travelled by the solvent R_f = \frac{\text{distance travelled by the substance}}{\text{distance travelled by the solvent}} Rf​=distance travelled by the solventdistance travelled by the substance​

Give your answer to 2 significant figures.

[2]
Markscheme

Purity and separating mixtures Questions

  1. GCSE
  2. /Chemistry
  3. /Purity and separating mixtures

46 exam-style questions on OCR GCSE Chemistry Purity and separating mixtures. Each one has a worked solution and a mark scheme showing where the marks go.

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