Wednesday, 23 October 2013

Happy Mole Day!!!

Yes, it's mole day, but I'm not referring to a small furry mammal with no eyes that digs in the ground.  Nope - this is chemistry and so that you aren't totally confused (if you aren't already!) I am going to try and explain the mole to you.  And I really hope it makes sense because I have to do a test on it later today...

Behold, the periodic table:

Hopefully, one of the first things you noticed on the periodic table was that for each square, there are two numbers and one-three letters.  The letters are simply the abbreviation of the element that 'owns' the square, for example the top left square that says H is hydrogen.  The 8th square, O, is Oxygen.  Sometimes, element abbreviations use the Latin names instead, like number 26, Fe, is iron.  This may seem totally confusing, but it really isn't when you get used to working with the elements and their abbreviations.

By now you have probably figured out that the top numbers in each square indicate the position each element has on the table.  They have another purpose as well, but that is beside the point right now.  What I really want to show you are the numbers under the letters in each square.  For oxygen (O), it says 16.00.  For Hydrogen (H) it says 1.008 and for iron (Fe) it says 55.85.  These numbers are the amu of that element.  Amu is the shorthand for Atomic Mass Unit.  Basically, amu is what we measure the weight of atoms in, and as you are probably anticipating, it is a very, very small unit of measurement.  Infact, convert one amu to grams, and you get 1.66 x 10-24  grams.  If you're not sure how small that is, another way to write it would be 0.00000000000000000000000166 grams.  According to my chemistry book, that is about one trillion trillions of the weight of a house fly.  

So what has this all got to do with moles?  Well amu is so small that it is really awkward to work with it all the time.  And so we owe much thanks to an Italian scientist named Amedeo Avogadro who worked out a relationship between amu and grams.  He discovered that the amu numbers on the periodic table in grams always have the same amount of atoms in them.  That means that 16.00 grams of oxygen (O) has exactly the same amount to atoms as 1.008 grams of hydrogen (H) and 55.85 grams of iron (Fe).  That it is that number that we call the mole.  Asking a scientist for three moles of carbon is like going to Donut King and asking for three dozen donuts.  It represents a number.  

You are probably wondering what that number is.  One mole is equivalent to 6.02 x 1023  atoms or molecules.  So 16.00 grams of oxygen will always contain 6.02 x 1023  atomsof oxygen.  Pretty amazing, huh?

The same works for molecules.  If you have one mole of water, that would be two hydrogens to one oxygen.  Add up the amu numbers and you get 33.08 amu.  Switch that to grams and you have exactly
6.02 x 1023  water molecules.  Below are examples of one mole of different elements and compounds.

So that's that.  You now know about the mole.  You may be wondering why today is mole day.  Look at Avogadro's number again.  6.02 x 1023  is a mole.  Scientists use the mole so often, the twenty-third of the tenth month became mole day... but it didn't officially start until two minutes past six this morning!

One more thing.  You are probably wondering why I did a whole blog post on Mole Day.  When I first found out about mole day, it was less than a month since the last one, and I have been waiting all year to be able to use it, so HAPPY MOLE DAY!!!!  :P

Wile, Jay L. "Module Five." Exploring Creation with Chemistry. Anderson, IN: Apologia Educational Ministries, 2000. N. pag. Print.


  1. Donut King! Wait, what was the rest of it about?

    Mostly joking. It was a fascinating read.

    1. Hahaha! Yeah, I can relate. :P Thanks for the feedback - I was hoping that it made sense to someone other than myself. :)