Another way that a mixture can be made is through diffusion.

Diffusion is the spreading out of particles. Moving from a high concentration to a low concentration.

For example, look at the diagram below, in which pink ink is dropped in to a beaker of water. Because of the motion of molecules in water, the ink particles slowly mix with the water. The overall process is diffusion between the pink ink particles and the water particles.

Ink Diffusion Steps

1. When the ink is dropped in the beaker, the ink particles are bundled together at the top right. This means that there is a high concentration of ink at the top right of the beaker (there are a lot of ink particles per volume of water).

2. Diffusion means the ink particles will spread out from that high concentration to a low concentration. Which is why in the second beaker, the ink has spread out, but there is still a low concentration of ink on the left and bottom of the beaker.

3. In the third beaker, the ink particles have successfully spread across the beaker, which means the ink has been diffused in the water.

For diffusion to take place, there needs to be a difference in concentration, which is called a concentration gradient. For example, in the ink example above, the ink particles spread to the areas of the beaker where there was an uneven amount of ink particles relative to the water. The ink particles continue to diffuse if there is a concentration gradient

Diffusion in gases

This process tends to happen in gases, allowing substances to mix together. As gas particles are very spread out, they are able to move and vibrate quickly.

For example, a spray of perfume in one corner of the room will diffuse to the other side of the room, which will soon cause the whole room to smell of the perfume.

Diffusion in Root Hair Cells

In plants, root hair cells have a lower concentration of water inside the cell than in the soil (where there is a high concentration of water). Water molecules will move by diffusion, from the high concentration outside the cell to the low concentration inside the cell.

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Factors Affecting the Rate of Diffusion

FactorImpact on the Rate of Diffusion
TemperatureAs the temperature increases, the rate of diffusion increases. This is because the particles have more energy, so they will be moving faster
Size of particlesThe smaller the particle, the higher the rate of diffusion
State of MatterDiffusion does not take place in solids and diffusion is faster in gases than in liquids