A drinks manufacturer produces two products: a bottle of water labelled 'pure still water' and a sports energy drink described as 'a carefully designed mixture of water, glucose, salts and vitamins in exact quantities'. Explain why the sports energy drink is a formulation but the bottled water is not, and describe one technique that could be used to show that the bottled water is a pure substance.

Eduqas A-Level Chemistry — 1.1 Atoms, molecules and stoichiometry · 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 designed for a particular use and is made up of exact quantities of pure substances. The sports energy drink contains more than one substance – water, glucose, salts and vitamins – which are mixed together but not chemically combined, so it is a mixture and therefore a formulation.
The bottled water contains only one substance – H₂O – so it is a pure substance and not a formulation.
One technique to show that the bottled water is a pure substance is to measure its melting point (or boiling point). A pure substance has a sharp melting/boiling point, whereas a mixture melts/boils over a range of temperatures. A sharp, single temperature reading would confirm the water is pure.

Examiner tips

  • Define a formulation as a mixture of exact quantities of pure substances; state that the drink contains multiple components. Explain that bottled water is a single component, hence not a formulation. Mention a suitable technique – melting/boiling point – and why a sharp point indicates purity.

Common mistakes

  • Confusing a mixture with a pure substance; claiming the water is a mixture. Using a technique that does not distinguish purity, e.g. density alone. Failing to explain why a sharp melting/boiling point indicates purity.

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 sports energy drink contains more than one substance / contains water, glucose, salts and vitamins mixed together (not chemically combined)
  3. The bottled water is not a formulation because it contains only one substance / is a pure substance / is not a mixture
  4. Named suitable technique: measuring the melting point of the water (or stating it melts/boils at a specific/sharp temperature)
  5. A pure substance has a sharp melting/boiling point whereas a mixture melts/boils over a range of temperatures, so a sharp reading would confirm the water is pure

Key terms in this question

formulation · pure substance · mixture

Related

More Atoms, molecules and stoichiometry questions

▶ Try answering this question with AI marking (free) →