What is pure

The idea

In science a pure substance has no other substance in it: it consists of the same type of particles and cannot be separated into other kinds of matter by any physical process; it is either an element or a compound.

The word pure

A pack of milk says 'pure'. A scientist uses the word 'pure' in a different way.

In science, what does a pure substance contain?

• Only one kind of particle
• Anything that looks clean
• A little of everything

Pure or not

Open both tabs.

Pure in science

In common use, pure means unadulterated, with nothing cheaper added. In science, a pure substance has no other substance in it. Something that looks pure can still be impure if it is made of more than one substance.

A pure substance has no other substance in it and consists of the same type of particles. It cannot be separated into other kinds of matter by any physical process.

Notes

A pure substance has only one type of particle.

Check yourself

In science, a pure substance consists of …

A pure substance cannot be separated into other kinds of matter by any …

In common use, 'pure' means …

A product made of more than one substance is, for a scientist …

• different kinds of particles. That would be a mixture.
• the same type of particles — correct. Yes!
• only liquid particles. A pure substance can be a solid, liquid or gas. It has the same type of particles.
• thought. A physical process cannot separate it.
• name. No physical process separates it.
• physical process — correct. Yes!
• unadulterated, with nothing cheaper added — correct. Yes!
• one kind of particle. That is the meaning in science.
• very expensive. In common use pure means unadulterated.
• pure, because it looks pure. If it has more than one substance, it is not pure.
• impure, even if it looks pure — correct. Yes!
• always an element. It is a mixture, not an element.