The components keep their identity
Mix two things together and then take them apart again. What comes back out tells you what a mixture really is.
Activity 3.1.1 — method
Take about a teaspoon of hydrated copper sulphate and about a teaspoon of naphthalene. Grind them together in a mortar with a pestle until they are thoroughly mixed. Tip the mixture onto a sheet of paper and look at it.
At a glance you can no longer see that there are two substances there. What you have made is a mixture of two compounds. Now get them back.
Activity 3.1.2 — method
Put the mixture into a small beaker, add about 50 ml of water and stir well. Fit a filter paper into a glass funnel and filter the mixture into a second beaker. Let the solid left on the paper dry, then look at it on a watch glass. Look at the liquid that came through as well.
The observation
The powder left on the filter paper is naphthalene. The liquid that came through is blue, so it holds the copper sulphate — dissolved in the water rather than destroyed by it. Both substances came back.
Three things that activity shows
Every one of these is part of what the word mixture means.
The components do not react
Grinding copper sulphate with naphthalene made no new substance. The chemical nature of each component is unchanged by being mixed.
Each component keeps its identity
The naphthalene was still naphthalene and the copper sulphate was still copper sulphate — which is why the blue colour was still there to see.
Physical methods can separate them
Filtering is a physical operation: no reaction, no heat of reaction, nothing chemical. It was enough to pull the mixture apart.
So a mixture is
Mixture
Matter in which two or more components are mixed together without being chemically changed, and which can be separated again into those components by physical methods.
Component
Each substance that has been mixed in is called a component of that mixture. It is the word this whole chapter is built on.