The Mole as a Chemistry Kit Essential
October 13, 2016
Not THAT Mole, the other one.
In chemistry, The Mole is one the seven International System of Units which is used to measure the relative abundance of the components in a chemical reaction.
In the reaction represented in Figure 1, a discrete amount of Carbon Dioxide and Water are combined in the Chloroplasts of a Plant to produce a distinct amount of Oxygen and Glucose.
“Unfortunately, it is not possible to measure out individual atoms. Atoms are small. In the lab, small isn’t manageable”.
Now grams, there’s a useful unit. How do we get from atoms to grams? Enter The Mole.
The Mole is based on the Carbon-12 Atom. Carbon is a good element to work with since it is easy to obtain in large, pure and inexpensive quantities. But, while a pile of carbon seems uniform there are various forms of carbon, e.g.14C, 12C, 16C, each of which differ in the number of neutrons in the nucleus of the atoms. Luckily though, these different forms, or isotopes, of carbon exist in stable relative amounts and essentially average out to a representative Carbon-12 atom (Figure 2).
Where to now, Well as Willy Wonka said: “We are the Dreamers of the Dream”, so a standard was set. A Mole of a substance is the relative gram equivalent of 12 grams of Carbon-12, essentially a gram for each nucleon in any atom or molecule. Going back to our Photosynthesis example above then, we can say that 6 Moles of Carbon Dioxide (264 grams) plus 6 Moles of Water (108 grams) becomes 1 Mole of Glucose (180 grams) plus 6 Moles of Molecular Oxygen (192 grams)……..372 grams of reactants in 372 grams of product out…..those are numbers that we can work with, and for bench research that is EXACTLY what we do.
For the sake of completeness, can we now go back and say how many atoms or molecules of a substance there are in a Mole? Yes. That value has been calculated to be 6.022 x 1023/mole. In honor of his extension contribution to chemistry, this constant was named after Lorenzo Romano Amedeo Carlo Avogadro di Quaregna di Cerreto (1776-1856), NOT pictured here.
I know that may seem like a long walk, but The Mole is a Cornerstone Concept in Chemistry. There can be NO practical application in science and medicine without it.
Further Reading: Home Library Essentials
Schaum’s Outline of College Chemistry (2013) Jerome Rosenberg, Lawrence Epstein and Peter Krieger. McGraw Hill Education, Columbus, OH
The link above is for the “current” tenth edition, but shockingly, my ancient sixth edition is pretty much the same.