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Q & A: Why is Air a mixture?

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Q:
give me one reason why we believe that air is a mixtur?
- carolyn (age 17)
newcastle tafe, australia
A:
The best reason I can think of for why we believe that air is a mixture is that freezing air slowly yields different liquids at different temperatures. Liquid nitrogen has a different boiling point than liquid oxygen. They also freeze at different temperatures. If air were only 1 compound, then air in its entirety would have a single boiling point and a single freezing point.

Jason (w. mike)

(republished on 07/24/06)

Follow-Up #1: air mixture?

Q:
air is not a mixture because of scientists freezing it and finding different liquids, it is a mixture because the compounds that make up air e.g. oxygen (o2), Carbon dioxide (co2) and the most important Nitrogen which is an element and makes up 78.09% of air are not chemically bound in the way that compounds are because they can be separated easily and there has been no change in state to any of the compounds or elements in air! and I'm only 12 years old HA HA!!
- Jon Harvey (age 12)
Birmingham, United Kingdom
A:
Jon- Your description of air and your definition of mixtures are good. However, we were asked why we believe that air is a mixture. In other words, we were asked for evidence. The sort of facts you cite were not discovered by reading textbooks but by doing real experiments. Once the experiments are done,  somebody can use our discoveries and put them in textbooks, and kids can read the claims and believe them. Usually they'll be right, but if nobody asked what the evidence was we'd never find out when they're wrong.

Mike W.

(published on 01/28/09)

Follow-up on this answer.