Reversible changes and separation methods

In a nutshell

Many changes are reversible. Reversible changes include the separating of some materials and a change of state.

Mixing materials

Materials can be mixed together.

Example

Solids can be mixed with liquids by dissolution.

Most of the time these mixtures can be separated again afterwards, there are a number of ways this can be done.

Note: Sometimes when substances are mixed with others they change form. Some of these mixtures are still reversible.

A solution is a solid that is dissolved in a liquid.

Example

Sugar dissolved in water forms sugar water (sweet drinks).

Science; Materials; KS2 Year 5; Reversible changes and separation methods

Reversible changes

A reversible change will end up with the same substances you started with.

Separation processes

Filtration

Filtration is the separation of a solid-liquid mixture using a filter. The solid and liquid products are formed separately, where the liquid falls through the filter but the solid will be trapped, not passing through. A filter contains small holes to collect solid products.

Procedure

1.	Add a separating funnel to the conical flask.
2.	Insert some filter paper into the funnel.
3.	Pour the mixture through the filter paper.
4.	Collect the liquid in the flask below and the solid that is trapped on the filter paper.

Example

Filtering the salt from the water in salt water. Salt will be left on the filter paper and the water in the flask.

Science; Materials; KS2 Year 5; Reversible changes and separation methods

1.	Beaker containing the mixture.
2.	Filter paper.
3.	Residue.
4.	Funnel.
5.	Conical flask.
6.	Filtreate.

Sieving

Sieving is the separating of larger solids and smaller solids. Smaller solids will pass through the sieve. Compared to filters, sieves will have much larger holes.

Example

Separating large rocks from smaller stones in dirt.

Evaporation and condensation

Evaporation and condensation is used to separate a solution (solid dissolved in liquid) by heating and cooling to form the original solid and liquid.

procedure

1.	Heat the solution and evaporate the liquid.
2.	Collect the left over solid when all of the liquid has evaporated.
3.	To collect the liquid the solution must be cooled (condensed) while it evaporates.

Change of state

A change of state is always a reversible process.

Examples

When heated, a solid metal will melt to a liquid metal. However, after being left to cool the liquid metal will harden turning back to a solid metal.
When a solid ice cube is heated it will melt into liquid water. When the liquid water is placed in a freezer it will turn back into a solid ice cube again.