Search results matching tags 'teaching science' and 'fire'

Elementary science: playing with fire

Anonymous — Sun, 17 Jul 2011 17:33:00 GMT

Fire is obvious, so it seems. Pretty much every child recognizes the flame of butane lighter is the same as the flames on the stove or on a lit candle.

A child sees that a fire makes solids things smaller. The grown-ups tell children that fire consumes, that the logs burned up, that fire reduces things to ash.

And pretty much every adult who believes this still lives in the world of alchemy, hoping to turn urine into gold—how else explain the popularity of state lotteries and the Tea Party?

My September sophomores know what fire is, no surprise, since September sophomores know everything there is to know about anything.

Before I ever say the words respiration or calorie, I ask them about fire—a few look confused (a good sign in science class), but most give me a knowing smile—they know what it is, they “just can’t put it into words” and when they do, they describe the properties of fire. Not a bad start.

I ask them what you need for a fire, and they know that—fuel, oxygen, something to light it—somewhere in elementary school they learned about the fire triangle.

I then pretend to take out a box full of pure oxygen, and ask them what would happen if I lit a match in it.

***

Most of my sophomores know the photosynthesis/respiration equation before they get to my class:

C₆H₁₂O₆+ 6O₂ => 6CO₂ + 6H₂O with energy released

Sugar + oxygen combined releases carbon dioxide and water

CO₂+ H₂O => C₆H₁₂O₆ + O₂ with energy captured

The kids love writing down equations, it gets them feeling all sciency, and now the stupid teacher isn’t asking stupid questions about stupid fire expecting answers that “can’t be put into words.”

The inevitable “Do we have to know this?” comes from the back corner of the classroom—always the same back corner—but I pretend I don’t hear.

I hold up my propane torch—even the back corner crowd notices now. I promise them I will light it in a minute, but they have to answer a simple couple of questions first. What do I need to make it work. (“Well, duh…”), and what is H2O (“Well, duh…” with an advanced eye roll).

I write the equation for the combustion of propane on the board—it’s similarity to the respiration/photosynthesis equations is glaringly obvious, but not a point I care to make at the moment.

C₃H₈ + 5O₂ => 3CO₂ + 4H₂O

I ask what comes out of the propane torch after the propane as the propane is burned. I consistently get two answers—fire and carbon dioxide. I never get water. I’ve asked hundreds of kids the question, with the equation sitting up on the board, and it’s like H2O is some mysterious stuff stuck to the equation just to make it balanced. The stuff is pretty mysterious when you get down to it.

After our list of stuff that comes out of the torch is made—usually CO2, heat, light, flame, and occasionally propane—I light the torch.

I pass the torch over a cool piece of glass—it could be a large beaker—then pass it over the cool stem of the faucet. The students see the flash of water vapor on the glass. They know it looks like” fog”—but no one wants to say it. It makes no sense. Water from fire? It must be a trick.

To be fair, it pretty much gobsmacks me, too, each time I do this.

And of course, water does not come from fire—it comes from the hydrogen in the propane and the oxygen in the air. Turns out we’re all closet alchemists. We cannot except the obvious.

***

Chemistry hit puberty when LaVoisier realized that fire consumes nothing—it only transforms. If you figure out the amount of stuff with and compare it to the stuff you end up with, it has the same mass.

Exactly the same mass.

All the heat and light and noise that escaped from the dancing flame took nothing away. Energy has no mass, no inertia, no stuff to it.

If you do not grasp this, do not attempt to teach anything about fire to children. Let them observe a candle, and when they ask you what fire is, let them know you really don’t know.

We already have a nation of alchemists voting, with predictable results.

Matchstick photo by Sebastian Ritter via Wikipediaa under CC.

The fire within

Anonymous — Wed, 29 Dec 2010 01:24:00 GMT

I warmed myself up tonight, shoveling snow off a patch of concrete. Orion, lying awkwardly on his back, shivered above as he aimed his bow at Taurus snorting high in the southwestern sky. On my way in, I grabbed a handful of Brussels sprouts, plucked off the plant now surrounded by snow.

Winter is here, as good a reason as any to talk about our inner fire.

***

I love blasting my propane torch, flashing flame on steel faucets, a blush of condensation dulling the metal, water from fire. (Yep, a lit propane torch emits water--go ahead, check for yourself.)

Electrons trapped in high energy states tumble into the welcoming arms of oxygen, screaming with delight, releasing light and heat as they settle into their pajamas, ready for rest.

Yes, of course, I broke a few rules there. And, yes, of course, it's not quite accurate.

It's closer than you might realize.

***

Our cells need oxygen gas for one reason only--to accept electrons released from food as they travel down their energy gradients, settling into basal states of energy.

The oxygen accept the electrons (and associated protons) to form water. This happens in the innermost regions of our mitochondria, ancient critters subsumed by our forbears.

When you get down to it, we really don't need oxygen at all. Our mitochondrial slaves need it. If a cell doesn't have mitochondria, it has no need for oxygen.

Our red blood cells, designed to carry oxygen, use none of it themselves. They have no mitochondria, no need for oxygen. That's why you can keep RBC's packed in plastic bags waiting to be transfused.

***

Mitochondria are organelles, membrane wrapped particles in your cells that help convert food into a useful form of energy called ATP. Think of ATP as cash energy--no matter where you need a shot of energy in a cell, ATP can provide it.

(ATP works by adding instability to compounds--it's like when your crazy Aunt Margarita crashes onto the Thanksgiving table. Things are going to happen.....)

Mitochondria have their own DNA, most closely related to bacteria than to you. They reproduce on their own. They are an alien life form that's been coexisting with larger cells for a long, long time.

This is so freaky I don't think it registers with most of my students. Mitochondria allow us to "burn" food down to carbon dioxide and water, releasing the energy caught by chloroplasts in plants.

***

What is fire? What happens to the fuel, to the oxygen?

Most adults here cannot answer this question, and it's pointless if your goal is to make money or get the girl or glom power.

Children love the question, and I doubt most ever get a decent answer. Heck, I know my students don't.

We teach chemistry as if it was handed down by Moses himself, the 10 Commandments in one hand, the Periodic Table of Elements in the other. I show them over and over and over again that water comes from a flame, and few can remember this two minutes after the demo is done.

***

Oxygen gas gets to your mitochondria by bouncing randomly around the inside of a cell. Since most of our cells burn a lot of food, their oxygen concentration is low relative to the fluid bathing them.

Just as fart molecules bumble their way across the room to embarrass their producer, oxygen molecules bounce around inside cells until they wander into a mitochondrion.

Red blood cells carry the oxygen molecules through our vessels, and they get dumped off where the oxygen concentration is lowest, needed only by the mitochondria, to produce the ATP needed to keep us alive.

This all happens very, very fast.

How fast? Cyanide blocks electrons from reaching oxygen inside the mitochondria. killing within minutes.

No oxygen, no fire, no life.

I have felt bodies quickly cool moments after death, no longer warmed by the trillions of mitochondrial furnaces within.

The shot of Orion is by John Gauvreau found at NASA's "Astronomy Picture of the Day."

Mitochondrion photo from Allen L. Bell, Ph.D, UNE COM here.

"Mad science" is redundant

Anonymous — Tue, 13 Jul 2010 11:39:00 GMT

That's a Tesla coil. It makes lightning.

It was built by a friend of mine--here's where he talks about it. It's worth a read (or two).

We did some incredibly stupid things back in high school, and we still have all our digits (amazing) and no juvie records (also amazing).

***

Ms. Lehman was my high school chemistry teacher--she regularly made things gurgle, glow, boom, and smoke. She had a perpetually amazed look on her face, but maybe that was her perpetually scorched eyebrows. She loved chemistry.

We dabbled a lot in lab--not something openly encouraged, but if you had a clue of what you were testing (and not just randomly mixing chemicals), you could try it.

I wanted to make laughing gas--nitrous oxide. My chemistry was OK, but not great, and I figured I might generate some if I poured nitric acid on a penny. Something went wrong, or rather, matter behaved as matter will, and a billowing red-brown cloud of toxic fumes erupted from the flask. Pennies are not just copper, maybe I misread the metal reactivity table, who knows....

I had enough sense to get it under the fume hood. I did not get expelled.

While I still light things on fire in class, I don't ignite hydrogen bubbles. I don't (intentionally) blow things up. I don't keep snakes in the class, nor spiders, or anything else that might prove upsetting. No potassium dropped in water. No microwave plasma balls.

Heck, I went through a whole year in class without leaving a stain on the ceiling.

***

Would you try this in class? (I'd modify it, of course--the lack of safety goggles is appalling, and why use your mouth when a squeeze bulb would do.)

As my class leaves on Fridays, I dismiss them with a question.

What do we practice? Safe science!

But if real science about teasing the unknown, can it be truly safe? Will any of my students be building lightning boxes in their garages when their in their 50's?

A confession: Ms. Lehman was absent the day I made NO2--she wasn't stupid.
She did take into account my explanation, though, and
while she officially chastised me, I think I saw her wink when she did....