A sports drink manufacturer produces a new energy drink containing water, sugar, food colouring, vitamins and flavourings. Explain why this energy drink is described as a formulation rather than a pure substance, and explain how paper chromatography could be used to show that the food colouring in the drink is not a pure substance.

WJEC A-Level Chemistry (Wales) — 1.3 Chemical bonding · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

A formulation is a mixture made up of a number of pure substances that are combined in specific proportions for a particular use. The energy drink contains water, sugar, food colouring, vitamins and flavourings – more than one substance that are not chemically bonded together, so it is a mixture rather than a pure substance.

Paper chromatography can show that the food colouring is not pure. The colouring is applied as a spot on a strip of paper (the stationary phase). A solvent (mobile phase) is allowed to rise up the paper by capillary action. The different components of the colouring dissolve in the solvent and are carried upward, but they have different solubilities and affinities for the paper. Consequently they travel different distances, giving separate spots. If the colouring were a pure substance it would give only one spot; the appearance of more than one spot proves it is a mixture.

Examiner tips

  • Use the definition of a formulation – mixture of pure substances in fixed proportions.
  • Explain that the drink contains several distinct substances not chemically combined.
  • Describe the paper chromatography set‑up and how components move with the solvent.
  • State that a single spot indicates purity, multiple spots indicate a mixture.

Common mistakes

  • Confusing a mixture with a solution; not emphasising the lack of chemical bonding.
  • Failing to mention that the solvent is the mobile phase and the paper is the stationary phase.
  • Assuming the colouring is pure because it looks uniform; not recognising multiple spots on the chromatogram.

Mark scheme (5 marks)

  1. A formulation is a mixture designed for a particular use / made up of exact quantities of pure substances
  2. The energy drink contains more than one substance / element or compound not chemically combined, so it cannot be a pure substance
  3. In paper chromatography the food colouring (mobile phase / solvent) travels up the paper (stationary phase), carrying the components of the colouring with it
  4. Different substances in the food colouring travel different distances up the paper because they have different solubilities in the solvent
  5. If the food colouring produces more than one spot on the paper, it is not a pure substance / a pure substance would produce only one spot

Key terms in this question

formulation · pure substance · paper chromatography

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