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Chemistry Mole 25,172 views

Teacher/Instructor Kendal Orenstein
Kendal Orenstein

Rutger's University
M.Ed., Columbia Teachers College

Kendal founded an academic coaching company in Washington D.C. and teaches in local area schools. In her spare time she loves to explore new places.

In chemistry, the mole, also called Avogadro s Number, is a unit that is useful in converting between atomic mass and molar mass. One mole is 6.02 x 10^23 of something, which was derived from the number of atoms in 12 grams of carbon-12.

Alright, let's talk about the mol and we're not talking about the mols you find on your skin or the mols that appear mum's garden we're actually talking about the mols you think Chemistry. We can also shorten that that mole to mol which we can do from now on. And that is S.I base unit used to measure the amount of a substance. And what does that actually mean? So actually our Avogadro, which is the chemist back in the early 1900's, he did many many many experiments with a with the element carbon and he actually found that carbon 12 meaning carbon with 6 protons and 6 neutrons, if he had 6.02 times the twenty third particles of C-12 they actually happened to be 12 grams which is amazing because these two numbers are the same and I'll show you why that's so amazing in just a second. If we you actually go a little bit further with this it's more. He actually discovered with that knowledge that these numbers these atomic masses that we find in the periodic table which is the average atomic mass of the of the particles are those isotopes are actually favor more of each substance or 6.02 times 10 to twenty third of each atom that number is actually mass that it has so if we had a mol of potassium ions oops sorry atoms they will be 39.09383 grams so that number actually is amu grams which is awesome so if we go back to this number and we actually take a look at this number we have 6.02 with lots of zeros behind it that number is enormous its hopefully gives you an idea of how big this number actually is.

If we had a mol of marbles it would actually cover the earth with a depth of 4 miles that is insane that's huge I just hope hopes that gives you an understanding of how big this number actually is which then in turn should give you an understanding of how tiny tiny tiny the atom is it's only 12 grams of carbon is these many these many atoms carbon atoms which should shows you how tiny tiny tiny atom carbon atoms actually are which is amazing.

Okay let's actually put this number to use, so we understand that we have dozen and the mol in dozen are actually the same kind of concept if we have 3.5 dozen roses how many roses do we have? Well we know in one dozen we have 12 roses let's use this information so let's put it 3.5 dozen roses and down here on the bottom. I'm making basically ratio down here we're going to have for roses because just like in dozen roses because just like in Math if something with top the ratio and the bottom of the ratio they can cross out so we know we have in one dozen roses we have 12 roses so these units can cross out because one is on top and one is on bottom we're left with roses great 3.5 times 12 is 42 roses so we know that 3.5 dozen roses is 42 roses okay fair enough, let's continue and start using the word mol so let's say instead of two 3.5 dozens let us say we have 2.5 mols of roses. How many roses do we have? Well let's do it again so we say 2.5 mols of roses, one mol of roses is 6.02 times 10 the twenty third roses right? Because one mol equals that many roses that unit can cross out we're left with roses if we multiply this number together 2.5 times 6.02 times 10 to the twenty third, we get 1.505 times 10 to the twenty fourth roses, it's a lot of roses.

Let's start using this number that mols when we're dealing with molecules and atoms and this is when you're going to see most. First here we have 9.03 times 10 to the twenty fourth molecules of water particles and how many mols of water do we have? Well kind of the same thing so we're going to say 9.03 times 10 to the twenty fourth molcule of water we know that we have one mol of water is 6.02 times 10 the twenty third molecules right? Cross out molecules because one's in top one's in bottom we're left with this mol. This actually gives me 1.5 mols of water an easier way to write this rather than having that whole long number that's my answer.

Now the next question is how many mols of hydrogen atoms do I have? Well I know I have 1.5 mols of water but if we look at water its H2O so it's twice as many hydrogen atoms as I did my molecules of water so I can just simplify multiply this number by 2 so 1.5 times 2 is 3 I have 3 mols of hydrogen atoms in 9.03 times 10 to twenty third molecules of water.

This is just the beginning of using the mol but hopefully you understand where the mol comes from and what it actually means and how we can use it in future.