1. 
What is a pure substance?

2. 

A pure substance melts and boils at temperatures.

3. 
The boiling point of oxygen is −183 °C.

4. 

Pure water has a melting point of 0 °C and a boiling point of °C.

5. 
What is the melting point of sulfur?

6. 

Common salt (sodium chloride) has a melting point of 801 °C and a boiling point of °C.

7. 
At room temperature (25 °C), which of these substances is a liquid?

8. 

If the melting point of a substance is below 25 °C and its boiling point is above 25 °C, the substance is a at room temperature.

9. 
Carbon dioxide sublimes at atmospheric pressure instead of melting into a liquid.

10. 

Copper has a melting point of 1083 °C and a boiling point of °C.

11. 
An impure substance often melts or boils over a range of temperatures instead of at one precise point.

12. 

Because of its impurities, seawater freezes below 0 °C and boils 100 °C.

13. 
When all the water in seawater has evaporated, what is left behind?

14. 

Seawater is impure .