The particulate nature of matter - Chemistry - page 7

Questions
1 When a jar of coffee is opened, people in all parts of the
room soon notice the smell. Use the kinetic theory to
explain how this happens.
2 Describe, with the aid of diagrams, the diffusion of
nickel(ii) ii ) sulfate solution.
3 Explain why diffusion is faster in gases than in liquids.

Brownian motion
Evidence for the movement of particles in liquids
came to light in 1827 when a botanist, Robert
Brown, observed that fi ne pollen grains on the
surface of water were not stationary. Through his
microscope he noticed that the grains were moving
about in a random way. It was 96 years later, in
1923, that another scientist called Norbert Wiener
explained what Brown had observed. He said that
the pollen grains were moving because the much
smaller and faster-moving water particles were
constantly colliding with them (Figure 1.16a).
This random motion of visible particles (pollen grains)
caused by much smaller, invisible ones (water particles)
is called Brownian motion (Figure 1.16b), after the
scientist who fi rst observed this phenomenon. It was used
as evidence for the kinetic particle model of matter (p. 3).

Figure 1.14 Hydrochloric acid (left) and ammonia (right) diffuse at
different rates.

Figure 1.16a Pollen particle being bombarded by water molecules.

a b
Figure 1.15 Diffusion within nickel(ii) ii ) sulfate solution can take days to
reach the stage shown on the right.

Figure 1.16b Brownian motion causes the random motion of the visible
particle.