Day 01 - Calculate the Mass of Air

As you learned in physical science, all matter has mass and takes up space. Similarly, you should have learned that air is a (gaseous) fluid, comprised of a number of different molecules. And although the air in, say, Beijing has different molecules than the air at the top of Mount Everest, scientists have agreed upon a generic composition of air. Please note that these ratios are shifting over time, as more carbon dioxide and methane - among other molecules - are pumped into the atmosphere. Thus, there will be some inaccuracy to our calculations today, but it is useful for us to know how this is done and, in doing so, to better appreciate the different weights of each molecule. We'll deal with that issue again in our next unit, on hydrocarbons.

I am going to demonstrate a simple chemical reaction and I will use it to put out a fire (a lit candle in a jar). The chemical reaction is as follows:
  CH₃COOH + NaHCO₃ + heat → CH₃COONa + CO₂ + H₂O

To puzzle out what happened I will provide you with a reference table reflecting the various generic molecules to be found in "clean" air. We'll talk a bit about how to calculate molecular mass (which you should already know how to do from your chemistry class), from which we could calculate the mass of a liter of air and compare it against the mass of a liter of pure carbon dioxide.

But we don't need to crunch all those numbers to figure out what we really need to know, which is why did the candle get extinguished in the demonstration I performed at the beginning of the bell. To answer that, we need to figure out:

1. which molecule makes up most of the volume of air?
2. is it relatively heavy or relatively light?
3. which molecule is essential for sustained combustion?
4. is it relatively heavy or relatively light, and by how much?
5. is carbon dioxide relatively heavy or relatively light, and by how much?

Combustion

any exothermic reaction in which oxygen combines with a fuel