What pure means here
Show on a big screenA jeweller sells "22 carat gold". Here 22 carat means 22 parts in 24 are gold. Is it a pure substance?
A particle is a tiny piece of a substance.
- Two samples, before you look inside.
- Sample A: every particle is the same. One substance.
- Sample B: two kinds of particle. A mixture.
A pure substance has only one kind of particle. A mixture has two or more substances. Each one is a component of the mixture. The other 2 parts of 22 carat gold are other metals. So it is a mixture.
A physical step, such as using a sieve, makes no new substance. To react is to change into a new substance.
The rule
A pure substance has only one kind of particle. It cannot be split by physical steps. A mixture has two or more substances. Each one is still there. The substances do not react with each other.
| Ask this | Answer | Which kind |
|---|---|---|
| How many substances are in here? | One | Pure substance |
| How many substances are in here? | Two or more | Mixture |
Watch out!
A label that says "pure" does not decide it. Count the substances.
Sort seven samples. Count the substances in each.
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Try the lab to finish this lesson.