carbon dioxide

A heavy colorless gas CO₂ that does not support combustion, dissolves in water to form carbonic acid, is formed especially in animal respiration and in the decay or combustion of animal and vegetable matter, is absorbed from the air by plants in photosynthesis, and is used in the carbonation of beverages.

The CO₂ molecule is linear with the carbon atom in the centre between two oxygen atoms which are both double bonded to it.

O=C=O

Although the bonds are quite highly polarised as they are colinear there is no permanent dipole on the molecule. There is however a vibration mode of the molecule that bends it out of line and generates a temporary dipole moment.

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In liquid form carbon dioxide is used in fire extinguishers for electrical and similar fires as it does not conduct electricity. However it is not a good idea to use it on computer equipment as it can scramble magnetic information (due to the temporary dipole) - that's why they used to use Halon in computing centres.

Solid carbon dioxide is more commonly referred to as dry ice. It is a white powdery solid.

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Carbon dioxide is toxic in relatively high concentrations. This is because haemoglobin works by complexing with oxygen or carbon dioxide to carry them round the body (oxygen in/carbon dioxide out). This is a very finely balanced equilibrium and if the external carbon dioxide concentration rises too high then it prevents the red blood cells from picking up oxygen in the lungs. This is the reason that the Apollo 13 astronauts had to get their carbon dioxide scrubbers working again (despite not being low on oxygen).

Carbon Monoxide on the other hand forms so stable a complex with haemoglobin that neither oxygen nor carbon dioxide can displace it at atmospheric pressures.

Thanks to Tiefling and Rollo who told me that this explanation was not originally clear enough.

High school sophomores have firm convictions:

Neil Armstrong never walked on the moon.
We will all die in 2012.
Aliens walk among us.

In class I try to avoid opinions. In the short run, many of my lambs will remain confused. It is not my job to convince Amanda that Neil Armstrong walked on the moon--as soon as I use my position of authority to make a point, I've lost my chance to teach a child how to think.

It is my job, however, to make them skeptics, to have a sense of what we do not know, to suspend judgment while using their God-given senses and rationality to come to their own conclusions, conclusions that might change should new evidence become available. As a result, I fear that some day a mother will tell my principal that I did not vigorously dispel the notion of aliens, of rigged moonwalks, of the impending doom 3 short years away.

Or maybe the parents believe these things, too.

One of the hardest things in high school science is convincing kids that gas is made of stuff. Bring in a chunk of dry ice, place it on the teacher's desk, and let it sublimate its way to nothingness.

"What happened to the dry ice?"
(My students look puzzled at the idiot asking the question)
Um, it, uh, disappeared?
"Yes, but what happened to the carbon dioxide?"
(Eyes roll. The teacher is either really deaf, really slow, or reaaaaaalllly annoying.)
We already told you.

And they did.

An American artist (from L.A., in a dish of delicious irony) has sculpted a giant box of flashing images, to represent a metric ton of carbon dioxide. It was unveiled for the UN Climate Change Conference in Copenhagen, and will travel a bit for the next few years, proving that all sides are capable of lunacy.

I would be impressed if the box swelled up with rising temperatures, or shrunk when a high pressure weather system passes through. But it doesn't. A reporter or two has mentioned that the cube represents the volume of CO₂ at standard pressure--but fail to mention temperature. Maybe the ideal gas law is too complicated to discuss. (It's not. But it's more fun to be mesmerized by flashing boxes of lights than to think.)

If you want to show children how much a ton of carbon dioxide weighs, show them the solid product of a very common reaction. Show them a block of oak, a cup of sugar, or a bowl of salad. Ask them where most of the plant "stuff" comes from. Take them outside and show them your town's largest oak tree. Comes from the same stuff.

CO₂ + water --> plant stuff and (bonus!) oxygen

The oxygen comes from the water, it turns out. All the carbon dioxide ends up in the wood. It works the other way, too. Burn sugar completely, and you get this:

plant stuff and oxygen --> CO₂ + water

You can show this in class. I keep a propane torch handy. Light it, briefly aim the flame at something cool and non-flammable (the faucet on my desk makes a good target), and see the water vapor fog up on the object. It amazes me every time.

Water from fire. (When you hold your hand over a lit grill you can get the same effect--that's not sweat on your palms.)

The global warming "debate" has broken down into camps of rival religious groups. You can still read the science behind the news. Good science requires skepticism, a point lost in the noise from the mob.

Science gives us knowledge, but not wisdom.

Technology gives us power, but not principle. Power without principle, knowledge without wisdom, will spell the end of our species, though perhaps not through global warming. There may be a reason intelligence per se is not an adaptation found in most species.

Life has been around for here for over 3 billion years, and I've no reason to believe it won't be around for billions more. I know I won't be around to see it. It would be nice, though, if one of my descendants does.