Mixtures

A mixture contains different substances that are not chemically joined to each other. For example, a packet of sweets may contain a mixture of different coloured sweets. The sweets are not joined to each other, so they can be picked out and put into separate piles.

A mixed pile of sweets is separated into four piles of different colours - red, green, yellow and purple
A horse-shoe magnet pulls iron filings out of sulfur powder
A magnet pulling iron filings out of sulfur powder

A mixture of iron filings and sulfur powder can easily be separated using a magnet. The iron filings are attracted to the magnet but the sulfur powder is not.

Dissolving

Dissolving is one way to make a mixture. For example, when salt is stirred into water, the salt dissolves in the water to make salt solution. In a solution:

  • the substance that dissolves is called the solute
  • the substance that the solute dissolves in is called the solvent

In salt solution, salt is the solute and water is the solvent. The particles of solute and solvent are completely mixed together.

Science presenter Jon Chase defines the terms solute, solvent and solution

Diffusion

Diffusion is another way to make a mixture. Particles of different substances mix together during diffusion. This happens:

  • quickly in gases, because their particles are able to move quickly in all directions
  • slowly in liquids, because their particles can move around each other, and they can push other particles around
  • not at all in solids because their particles can only vibrate on the spot
At first, the gas represented by red particles is concentrated on one area. After diffusion, they are no longer concentrated in one area and are mixed in with other gas particles in a more random wayDiffusion quickly spreads particles throughout a gas

Diffusion explains why the smell of cooking spreads through the house, and why a drop of paint spreads on its own through a jar of water.

You can find out more about diffusion in this Physics study guide.