Explain why a liquid takes the shape of its container but cannot be compressed into a smaller volume.

OCR GCSE Chemistry A: Gateway Science (J248) — C1.1 The particle model · Explain · 4 marks · View as Markdown

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

A nurse draws a liquid medicine into a syringe. When the nurse pushes the plunger with the needle blocked, the liquid does not compress. However, the liquid had previously poured freely into the syringe, filling the space available.

Model answer (4 marks)

1. In a liquid the particles are close together, almost touching each other.
2. Because there is no significant space between the particles, they cannot be pushed closer together, so the liquid cannot be compressed.
3. The particles are arranged randomly, not in a fixed or regular lattice.
4. The particles can slide past one another, allowing the liquid to flow and take the shape of its container.

Examiner tips

  • Use the word "close together" or "touching" for point 1. Mention "no significant space" for point 2. State "random arrangement" for point 3. Explain "particles can move past each other" for point 4.
  • common_mistakes
  • :
  • Confusing a solid’s fixed arrangement with a liquid’s random arrangement. Saying the liquid can be compressed instead of explaining why it cannot.

Mark scheme (4 marks)

  1. Particles in a liquid are close together / touching
  2. There is no (significant) space between particles for them to move into, so the liquid cannot be compressed
  3. Particles in a liquid are arranged randomly (not in a fixed/regular arrangement)
  4. Particles can move past each other, allowing the liquid to flow and take the shape of the container

Key terms in this question

liquid · compress

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