How to Spot Pure Substances

how do you tell if an object is a pure substance without even knowing anything about it besides the color, shape texture, size, and so forth?
- anonymous (age 11)
Missouri, America :)

Phrases like "pure substance" don't have precise meanings that everyone agrees on. However, grabbing the Wikipedia definitions, which center around having a definite chemical composition, there is one type of pure substance that you could spot by eye. Say you see something that has all the symptoms of being a single crystal- the sharply defined faces, special angles at the points, etc. That crystal will often be a pure substance in the "definite composition" sense.  It could, however, consist of more than one type of molecule. Some crystals, called solid solutions, can keep their crystalline form with a variable ratio of some of the components, so there's no guarantee without some much less superficial data.

Mike W.

(published on 10/03/2011)