How can physical properties be used to identify substances?

If you match the physical properties of an unknown substance to the properties of a known substance, you now know what you've got. For example, if you know that compound X is bright yellow and screams when you poke it, an unknown sample that is yellow and screams that you poke it is probably compound X.

Of course, chemicals usually don't scream. Here are some of the properties you might consider using instead:

• Melting and/or boiling point

• Examination of spectra (if you've got the right gear, that is).

• Hardness

• Color

• Smell

• Stickiness, shininess, viscosity, etc. Pretty much anything you can imagine.