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Old 12-05-05, 09:45 PM   #1
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What actually Is the MOLE, chemistry

Okay so today the Mole was introduced in chemistry class...
6.02x10 (super script) 23.

I dont know what it was, but that # was about all i got out of the class. Can somebody explain exactly what the Mole does? How does that # tie into the chemical world. Something about finding the # of atoms in a particle?
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Old 12-05-05, 09:50 PM   #2
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Funny thing is, you really didn't miss much. The mole is simply a conversion factor. 6.02x10^23 of anything is a mole of that thing. If I had 6.02x10^23 dollar bills, I would have a mole of dollar bills. (I would also be filthy rich.) The reason this conversion is useful is because it allows you to convert between your mass measurements on a human scale (grams) and measurements on a molecular scale (much smaller). For example, you can get the mass of a chunk of gold and see that it weighs 197 grams. Since gold has an atomic weight of 197, this means there is one mole of gold atoms in that chunk of gold, or 6.02x10^23 gold atoms.

Hope that helps.
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Old 12-05-05, 09:52 PM   #3
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From the wikipedia.

The formal definition of the mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 12 grams of carbon 12, where the carbon 12 atoms are unbound, at rest and in their ground state. [1] The number of atoms in 0.012 kilogram of carbon 12 is known as Avogadro's number. It is approximately 6.0221415×1023
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Old 12-05-05, 09:57 PM   #4
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By the way, as a point of trivia, the value known as Avogadro's number really is somewhat of a misnomer because it's not unitless. 1 = 6.02x10^23 /mol, or 1 mol = 6.02x10^23

If the first sentence of this post confuses you, don't worry about it. The more important thing to understand is the two mathematical equations. Basically, when you start needing to calculate things and get units to work out, remember one of those equations. (Either one's fine since they're equivalent equations.)
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Old 12-05-05, 10:00 PM   #5
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A mole is like a stone is like a slug is like any other of those funny units we have. Everyone else sumed it up real well, 1 mole is 6.626...x10^23 atoms where atoms is a unit of measure.
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Old 12-05-05, 11:00 PM   #6
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Thankyou very much folks, it makes much more sense now. Not sure how a 2 hour lecture got consolidated into a 6 thread post, but it works
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Old 12-05-05, 11:51 PM   #7
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We just did that last week.ug
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Old 12-06-05, 02:56 AM   #8
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It's an Avogadro's Number of something, and there's also molar, how many moles per liter of a solution. The handy thing about the mole is, you use that and the atomic weight to calculate how many grams of This chemical to mix with how many grams of That chemical, to get a reaction that goes without too much of This or That left over.
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Old 12-06-05, 03:37 AM   #9
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Avogadro... mole.

Avocado... guacamole!
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Old 12-06-05, 04:56 AM   #10
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Originally Posted by khuon
Avogadro... mole.

Avocado... guacamole!


I will have to remember that one, my students will get a kick out of it!
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Old 12-06-05, 10:55 AM   #11
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Molar uses a capital M; a 5M HCl solution has 5 moles of HCl in 1 liter of water. I use moles all the time, every day. But I'm nearly always in the mmole or micromole range. And the poor biochemists across the hall are used to nanomoles.

You can't say which is more, 5g of hydrogen or 5g of carbon? You've got to convert to moles. Then you can check the mole to mole ratio.

5g H x 1mole/1g H = 5moles H

5g C x 1mole/12g C = .417moles C (actually, if we're going to get into that whole significant figures thing, it would be just .4moles C)

So you got more Hydrogen atoms than Carbon atoms.

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Old 12-06-05, 11:55 AM   #12
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Somebody help me with this, because i know 22.4L fits in there somewhere. Maybe it's the volume of 1 mole of hydrogen at sea level at room temp? help?
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Old 12-06-05, 12:11 PM   #13
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Quote:
Originally Posted by Ubie
Somebody help me with this, because i know 22.4L fits in there somewhere. Maybe it's the volume of 1 mole of hydrogen at sea level at room temp? help?
For an ideal gas, PV = nRT, where
P = pressure
V = volume
n = number of moles
R = conversion factor
T = temperature

At standard temperature and pressure (STP), if you plug in the values for P, n, R, and T, you will find that one mole of gas takes up 22.4 L of volume. Note that the equation does not care what the molecular weight of the gas is, so (assuming ideal behavior) this is true regardless of whether the gas is H2 (MW = 2) or Xe (MW = 131).
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