I like fill-in-the-blank days. However, there is a problem with mole day. Mole day is, of course, 10/23. You know, a mole? One mole is 6.02 x 1023 Avogadro's number. Get it? 10 to the 23? Ok, before I go into mole problems, let me look at two other days.

Pi Day - 3/14

Obviously, this is a celebration of the number Pi. Really, one of the coolest numbers out there. As a bonus, Pi day is also Albert Einstein's birthday. So, what could you do on Pi day? You could look at the relationship between the diameter and circumference of circular objects. Very easy. Or you could calculate Pi using random numbers (that is what I did). The key point is that you can numerically relate circumference and diameter.

g-day - 9/8

I don't know if this geek holiday has caught on yet, but I am promoting it. This is a celebration of the local gravitational field (9.8 N/kg). What do you do on g-day? (which is not short for good-day, just so you know) You shoot stuff, you drop stuff. Really the possibilities are endless. Next year, I am thinking about dropping watermelons off a building and having viewers determine the local gravitational field. Key point - 9.8 is an accessible number.

The problem with mole day - 10/23

What can you do on mole day? The best thing would be to show a mole of something. A mole of aluminum is easy to show. That is just 26 or so grams. But big whoop. How does anyone know that is a mole? Can you see each atom of aluminum? No. Take an example. What about 1/2 - dozen day? Has anyone ever seen a dozen eggs?

So, the question is: can I show one mole of something that you could also see the individual pieces? Honestly, I don't know. But gosh-darn it, I am going to try.

How about a mole of salt grains? I can see an individual salt grain. How big would a mole be? The problem is that even a 1/4th of a teaspoon of salt has more grains than I would like to count. I don't have an 8th grader handy to count 1,000 grains. The next best thing is to cheat. I am good at cheating.

Here is a picture of 41 grains of salt. Oh, I know I can't really get the volume (the close-packing volume). But I can get the mass. You can't get the mass of 41 grains of salt. That is impossible, even for a computer. It's not impossible. We used to bulls-eye salt back in Beggger's Canyon and they are not much bigger than 2 meters.

Here is the cheating part. I used our Department's (Southeastern Louisiana University) analytic balance. With this, I get a mass of 0.0077 grams. Now, for the next part. Here is a graduated cylinder filled with salt. About 23 ml (sorry about the picture).

Using a normal balance, this salt has a mass of 29.4 grams. So, these salt grains (as packed like they are) have a functional density of (including the air spaces):

I don't want the mass density. I want the number density (how many grains per unit of volume). Just a little unit conversion gives:

Now we are getting somewhere. I know the number-density, so I can calculate the molar volume for grains of salt.

That is one big pile of salt. If you were to put it in a cube, it would be 44 km tall (27 miles) - yeah, that's high. Here, I made some images with Google Earth. For some reason, I put my giant cube of salt grains in Maimi, Fl. Here is what that would look like:

What if I were in Tampa, Florida? I could still see it. This is some random location near Tampa looking towards Miami.

What if you wanted to spread it out. You know, so you could see the top? In fact, that is enough salt to evenly spread over the surface of the Earth and be 17 cm thick.

Oh, I know - I could get smaller stuff. Maybe I could see something about 10 times smaller than salt. Right? That wouldn't help. Suppose that increases the number density by 1000 (that is 103). That would still make a cube that was 4 km on a side.

Avogadro's number is gianomrous. It is so big, you can't see it. And that sucks. Good thing I am not a chemist.

But wait, there's more

I can't help it. Let me do one more. What if I wanted a mole of popcorn seeds? Here are some poured in a beaker.

This is a volume of just about 20 cm3. Also, I counted these - 93. This gives a number density of:

A mole of popcorn seeds would have a volume of:

This would make a ball that has a radius of 3.1 x 105 meters. Here is what that would look like:

The salt grain cube is still there.

I can't stop. If the Earth was made of a mole of Lego bricks, each brick would be about 12 cm on a side.