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What is a Pure Substance ?

A pure substance is comprised of a single chemical element or compound.

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Lesson 2A: page 1 of 13

What is a pure substance ? That seems like an easy question, doesn’t it ?
A pure substance is any chunk of matter that has the same composition throughout.
That means that all of the molecules or atoms in the chunk of matter must be the same species.
If a beaker contains ONLY water molecules, then it contains a pure substance.
We have to be careful and not look at any chunk of matter smaller than about 100 mm. If we look much closer than that, we may start to notice the properties of individual molecules and atoms.
For example, we might notice that the oxygen in a water molecule doesn’t have the same properties as one of the hydrogen atoms.
So, we are really talking about a macroscopic piece of matter. This is called the continuum scale.

What is a Pure Substance ?

Ch 2, Lesson A, Page 1 - What is a Pure Substance ?