# Mixtures

## Mixtures

A mixture contains more than one substance.

#### Solutions

A mixture of salt and water is clear; you cannot see the salt. A mixture like this is called a solution.

We say the salt has dissolved. The salt is described as the solute and the water as the solvent.

solute + solvent = solution

When salt and water are mixed, the water particles get between the salt particles and separate them. The separate particles are too small to be seen, which is why the solution appears clear.

#### Suspensions

When a solid is placed into a liquid such as water and does not dissolve we say it is insoluble. Chalk is insoluble in water and appears as white specks when placed in the liquid. A mixture like this is called a suspension. In a suspension the particles of solid do not dissolve but form clusters that are large enough to be seen.

#### Disperse systems

Some mixtures have insoluble 'bits' in them which unlike a suspension are evenly spread throughout the other substance they are in.

Foams contain bubbles of gas (usually air) which are dispersed through a solid or liquid. An example of a foam is hair mousse.

Emulsions are made up of two immiscible liquids. Tiny drops of one are dispersed in the other. An example of an emulsion is eye make-up remover.

Gels are usually formed when a solid is mixed with a liquid. They have large molecules that attract each other, forming a web.

#### The effect of temperature on dissolving solutes

As you add sugar to water it dissolves quite slowly (at room temperature).However, eventually no more sugar will dissolve even with stirring. The solution is said to be saturated.

In the diagram below, notice that some of the sugar dissolves, but not all of it. The sugar that doesn't dissolve falls to the bottom of the beaker.

Stirring the water may make some more sugar dissove, but add more and more and - eventually, it will stop dissolving.

A saturated solution is one that can dissolve no more solute at that temperature.

So what happens when you heat the sugar solution?

At room temperature in the diagram above, there was some sugar left at the bottom of the beaker. But as the temperature is increased more of the sugar is dissoved. So sugar is more soluble in hot water!

If a solid is soluble in a liquid, it usually gets more soluble as temperature rises!