Pure and Impure Substances

What are pure substances made of?

One substance only (one element or one compound).

What is an example of a pure element?

Oxygen (O₂).

If you zoom in on pure oxygen gas, what would you see?

Oxygen atoms only (in pairs as O₂).

What is an example of a pure compound?

Water (H₂O).

If you zoom in on pure water, what would you see?

Water molecules only.

What are mixtures or impure substances made of?

More than one substance (two or more elements or compounds together).

What is a common example of a mixture of gases?

Air (mixture of oxygen, water vapor, carbon dioxide, nitrogen, etc.).

Name four examples of mixtures mentioned.

Air, milk, sea water, fruit juice, paint.

Is gold an example of a pure or impure substance?

Pure (if not mixed with anything else).

Do pure substances have a single melting/boiling point or a range?

A single melting and boiling point.

At what temperature does pure water melt?

0°C.

At what temperature does pure water boil?

100°C.

Do impure substances melt and boil at a single temperature or over a range?

Over a range of temperatures.

What happens to the melting point graph line for an impure substance?

It is not flat; melting happens over a range of temperatures.

What happens to the boiling point graph line for an impure substance?

It is not flat; boiling happens over a range of temperatures (boiling point gets higher than 100°C for impure water).

How can you identify a pure substance using melting and boiling points?

It has specific, single melting and boiling points (e.g., water melts at exactly 0°C and boils at exactly 100°C).