Practise Using Correct Terms for Describing Pure Substances

All matter can be subdivided into being pure or impure.

Pure substances are made up of only one type of element or one type of compound. As soon as there is even one molecule of a different element or compound in a pure substance, it turns it into an impure substance. 

So, if you drop a cube of sugar into a beaker of water, once the sugar particles have dissolved and mixed with the water molecules, it is an impure substance. 

The words you use when answering questions about pure and impure substances are really important. If you use a wrong word in your answer, it can change the whole meaning and so you may get the answer wrong.

Let's look at an example.

Question: What is a pure substance in chemistry?

Jodey's answer: A pure substance is made of only one thing.

What do you think of Jodey's answer? Which part would you change if you could?

'A pure substance is made of only one thing'

The use of the word 'thing' here would mean that Joedy's answer wouldn't get any marks. That's because a thing can be anything! It could be a biscuit, or a log!! "A pure substance is made of only one biscuit" 

It would be better if she changed the word 'thing' for 'element or compound'. A pure substance is made of only one element or compound. That's better, you'd get the marks for that answer now Jodey!

Let's try some questions!