# A student places a crystal of purple potassium manganate(VII) at the bottom of a beaker of cold water. After ten minutes, a faint purple colour is visible throughout the water. The student then repeats the experiment using hot water. Explain why the purple colour spreads through the hot water more quickly than through the cold water.

> Cambridge International IGCSE Chemistry (0620) — 1.2 Diffusion · Explain · 4 marks

## Mark scheme (4 marks)

1. Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration
2. In hot water the water (and potassium manganate(VII)) particles have more kinetic energy
3. Particles in hot water move faster
4. Therefore the potassium manganate(VII) particles spread / mix throughout the water more quickly

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-places-a-crystal-of-230a50df) · Published by Druglandscape Ltd.