Solids, liquids, and gas can sometimes be mixed together. For example, you can have a mixture of two or more solids, or you can mix a solid with a liquid. Sometimes, when a solid mixes with a liquid, the solid disappears. The solid is said to have dissolved, and this type of mixture is called a solution. It is fairly easy to separate any mixture back into the different things that formed it.
Separating mixtures
Mixtures can be separated back into their different parts. Choosing the correct method depends on what type of things the mixture is made up of.
Sieving
Sieving can be used to separate a mixture of solids, but the solids must be different sizes. Liquids containing large solids can also be separated by sieving. For example: a mixture of solids is passed through a sieve. The small bits of solid pass through the holes in the sieve. The sieve stops the big bits of solid from getting through.
Filtering
Mixtures of solids and liquids can be separated by a process called filtration. The mixture is passed through a fine mesh, such as filter paper, which holds back the solid bits, but allows the liquid through. For example: a mixture of a solid and a liquid is passed through filter paper. The liquid passes through the tiny holes in the filter paper. The filter paper stops the solid bits from getting through, even very small pieces of solid, such as grains of sand.
Evaporating
When a solid has dissolved in a liquid to form a solution, it cannot be separated by filtration. The solution must be heated until the liquid evaporates, leaving the solid behind. For example: a solution of sugary water is heated in a pan. The hot water evaporates. Eventually, all the water evaporates and solid sugar is left behind in the pan.
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