Re: What exactly is air?

This will arrive too late for the paragraph you have to write -- I'm sorry, but even mad scientists have deadlines. And besides, your teacher wants you to search for the answer yourself.

A "mixture" is any combination of two or more substances. Air certainly is that. There are three major classes of mixtures.

• suspensions are mixtures where one substance is divided into visible particles (.1 mm or larger) and dispersed through a second substance. Oil-and-vinegar salad dressing is a good example.
• colloids are mixtures in which the particles are too small to be seen visually, but still apparent through a light or electron microscope. Colloids can be classified by the phases of the particles and the substance they're mixed in.
  

  		Particle phase
  		solid	liquid	gas
  surrounding phase	solid	certain alloys	jelly	aerogel
  	liquid	ink	milk	shaving cream
  	gas	smoke	fog	none

  
  All colloids are able to scatter light -- that's why they generally appear white or hazy.
• solutions are mixtures in which the two substances are combined right down to individual molecules. There are no clusters of molecules anywhere. The substance being mixed is the "solute", and the substance doing the mixing is the "solvent". The terms "solid", "liquid", and "gas" don't apply to individual molecules, so a solution is generally wholly solid, liquid, or gaseous, unlike the colloids above.

  Air is a mixture of oxygen and nitrogen (and a few other things). It is almost completely transparent (when there's no smoke or dust), so it's probably not a colloid. The molecules of oxygen and nitrogen are intermixed completely, with no "lumps" of either. Therefore, air is a solution of a gas in a gas.

  I got the definitions of solution and colloid from Encyclopedia.com.

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