UCSB Science Line (2024)

Yes, indeed. A combination of lowtemperatures and high pressures results in thedifferent components of air condensing out asliquids. Air is about 78% nitrogen and 22%oxygen (the remaining components are mostly carbondioxide, water and argon, all in very smallquantities and can be neglected). First, theoxygen condenses into the liquid at 90.2 K (whichis negative 182.9 degrees C,) and then nitrogencondenses into the liquid at 77.4 K (which isnegative 195.75 degrees C). This process ofcondensation is in fact used industrially toseparate nitrogen and oxygen. When cooled further,these liquids freeze into solids.

Air is made up of several different gases,which all freeze at different temperatures. If youwere to place an air-tight box into an incrediblycold freezer, the gases would freeze at differenttimes as the box cooled, and so theoretically, youwould get layers of different frozen gases. However, there are so few molecules of any gas inair relative to the volume it occupies, youprobably wouldn't be able to see the layers. Instead, when you opened the box (assuming youcould do so without melting the crystals orfreezing yourself), you would probably just see afew crystals sprinkled on the bottom of the box.

The first gas to freeze would be water vapor. This is why the air is so dry in very coldplaces. Then carbon dioxide would freeze, and thennitrogen. The last gases to freeze would be oxygenand argon. At absolute zero, all the atoms in thedifferent gas molecules would merge into one atom(see the question this week on absolute zero ).

For scientists living at the South Pole in thedead of winter it can get as cold as minus 80degrees Celsius. This makes it very hard for themto breath outside without a special air supply. Atsuch cold temperatures, the carbon dioxide freezesand drops out of the air. (Remember that it isthe amount of carbon dioxide in our blood, not theamount of oxygen, that triggers our brain to takea breath. The scientists would pass out simply by"forgetting" to breathe.)

Yes, you can freeze air, and yes, eachingredientof air will freeze at a different temperature, sothat if you were to take a jar of air and slowlymake it colder and colder, each differentingredient would freeze into a different layer,just as you suggest.

Water, for example(which is often present in air as humidity),freezes at 32 degrees Fahrenheit, or 0 degreesCelsius. You can see this happen sometimes on coldnights, when there is frost on the windows. Thisfrost is moisture which used to be in the air andthen froze in a layer onto your window. If yourwindows got really cold: about -200 Celsius or-330 Fahrenheit, then the nitrogen in the airwould liquefy on your window, and at about -220Celsius or -365 Fahrenheit, it would freeze solid,giving you a layer of solid nitrogen. The otheringredients of air freeze at intermediatetemperatures.

The only gas which doesn'tfreeze solid is Helium. It liquefies at -270Celsius or -450 Fahrenheit, but it will neverfreeze solid unless you squeeze quite hard on it.