Chemical Misconceptions - Part II

In this, the second installment of my Chemical Misconceptions series, I'd like to turn to a few quick concepts that I encounter from year to year with my sophomores. I am continually surprised that many of these basic ideas are somehow missed throughout elementary and middle schools. What is more surprising (and not a little frustrating) is that many of these myths persist into adulthood. This post (along with the others in this series) is an attempt to spread a little correct information, and maybe to modify the way we describe the world around us.

The Color of Water:

Invariably, when asked to describe the color of water (or other such liquids that look like water), students will respond with the time-honored "clear". Honestly, I'm not sure of the origin of this one. I suppose that "clear" has become part of our culture as a way of describing things that have no color. It's also inaccurate.

The word "clear" is a synonym for transparent to visible light, or the ability to transmit light through a substance. Water certainly is clear - it transmits light quite well (although it does bend it slightly), but clarity is not color. The most appropriate term used to describe the color of water is "colorless", as in, having no color.

This may seem to be nit-picky and overly particular, but hey, this is science.

Heat Rises:

This expression is extremely commonplace in our culture, and also extremely wrong. We could prove this fairly easily: if heat rises, then it should be possible to take a hot pan directly off the stove and put it on top of our an unprotected hand (Note: Please, please, PLEASE do not attempt this at home - I take no responsibility for any trips to the emergency room with second degree burns on your hand). If heat rises, then a pan on top of your hand isn't going to do you any harm, because the heat would be moving upwards, away from your hand. Hopefully, you realize that this isn't the case (I hope you didn't have to prove it to yourself!).

The fact is, thermal energy, like all types of energy, flows from matter that contains a lot of it into matter that contains less of it. In the case of our hot pan, that means the heat is flowing from that pan right into your ivory-soft skin, and burning the bejeezus out of it (that's a technical term). It's not a directional thing, or, more accurately, it's an omni-directional thing. Thermal energy is radiant - it flows in all directions.

So, why then do we say that heat rises? Usually this expression is uttered in the context of keeping warm in your house. Why is it usually warmer upstairs - and let's not get into a lengthy discussion of the importance of proper home insulation. What we mean when we say "heat rises" is "hot air rises". Hot air is less dense than cold air, so the cold air will sink to the bottom of the house, pushing the warmer air upwards. This is essentially how hot air balloons work. It's not the heat that's rising, it's the warm air.

Is the Air There?

Somewhere in our lives, we have either been told or have constructed as a fact that the air isn't matter, because it cannot be seen. Those who escape this particular fallacy often get caught up in thinking that, while the air is matter, it is either the same thing as oxygen, or it is a single substance (element or compound). My personal thought on this is that it is entirely constructed belief - that is, no one told us this, we simply deduced it on our own. After all, the ancients didn't believe that the air actually existed, and when they did finally decide that it was there, they thought it was an element. Are we so much better than they were? Well, yes.

Matter is classically defined as anything that has mass and takes up space (volume). Because we cannot see the air, it isn't a stretch to think that it has no mass. Solids and liquids have mass that can be felt, but pick up a glass of air, and it feels, well, empty. Plus, proving air's mass is also not an easy thing to do, unless your name is Otto Von Guericke. Except actually, it's fairly easy to prove that air has mass, all you need is a meter stick, two balloons, some tape, and a pin.

First, blow up both balloons to be approximately the same size, and tape them to each end of the meter stick. Put identical crosses of tape on each balloon, then balance the meter stick on the end of a table (or lab bench, if you have one). You may need to move the balloons to get the meter stick to balance.

Now, carefully use the pin to poke a small hole in one balloon, right in the middle of the tape cross. Try not to pop the balloon, just make a hole so that air can escape. As the air escapes from one balloon you will see the meter stick begin to tilt upwards on that end. Where once the two balloons were balanced, the balloon that is losing air is now measurably lighter. The other balloon's mass (yeah, it has mass) is not changing. We can deduce that air has mass.

It's a bit easier to see that air does, in fact, take up space. As you blew into those balloons, they got bigger (their volumes increased). So air has both mass and volume, and is therefore matter.

Now, is the air a single element? For hundreds of years, it was thought that it was. In fact, early chemists thought that all gases were just contaminated air. The work of chemists like Antoine LaVoisier, Henry Cavendish, William Ramsay, and others has shown that in fact, the air is made of a combination of nearly twenty different gases, all mixed together in different amounts. Of course, the big three are Nitrogen (about 78.084%), Oxygen (about 20.947%) and Argon (about 0.934%) make up almost all of it. Each of these components can be physically separated from air, usually by distillation. The other components of air are present in much smaller amounts, and vary greatly with location (cities versus the country, etc.).

So there are three more ideas to share with your families around the dinner table. There are more to come, but I think that should keep you busy for a bit.