# Can someone explain moles and osmoles to me?

Asked by

simone54 (

7595)
February 15th, 2010

Yes, it’s for home work. I am not getting it.

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## 4 Answers

Okay, let’s start with something you are familiar with: a dozen. It doesn’t matter what the items are, if you have a dozen of something you have twelve.

Now let’s say you want to make 2 dozen cupcakes. A cupcake is complete when you have the cooked batter and it has icing on top. Now let’s say that you know how much batter weighs to make a dozen cupcakes and you know how much icing weighs to cover those dozen cupcakes, (and those weights are not going to be the same, they are relative to what is it you’re weighing). To make the two dozen cupcakes you weigh out 2 X how much batter you need for a dozen cupcakes. You weigh out 2 X the icing you need for a dozen cupcakes. You make the 2 dozen cupcakes and the amounts work out perfectly.

Switch gears, now you want to make one dozen NaCl. You take one dozen sodium (Na) atoms and one dozen chlorine (Cl) atoms, combine them together and you get 12 NaCl. However, getting the twelve atoms of each was pretty tricky. You remember back to making cupcakes and wish there were an easy way to weigh out sodium and chlorine and know that you had an equal count (atoms) of each element so that you could combine them together evenly. Well, you can! It turns out that amounts like a dozen are too small to be practical, but if you got 6.022×10^23 atoms it turns out to be pretty useful: 6.022×10^23 carbon atoms weigh about 12 grams, 6.022×10^23 sodium atoms weighs about 22.90 grams, 6.022×10^23 chlorine atoms weighs about 35.45 grams. Interesting. If you take a look at the periodic table the atomic mass of carbon is about 12, sodium is about 22.90, and chlorine is about 35.45. That 6.022×10^23 number is useful, but kind of awkward to use. Let’s just call it a “mole.” Nothing to tricky about it. When I have a dozen of something I have 12. When I have a mole of something I have 6.022×10^23.

If I want to make 1 NaCl: I take 1 Na and 1 Cl and I get 1 NaCl

If I want to make 1 dozen NaCl: I take 12 Na and 12 Cl and I get 12 NaCl

If I want to make 1 mol NaCl: I take 1 mol Na and 1 mol Cl and I get 1 mol NaCl

(however, we can look at the periodic table to see how much a mole weighs, let’s do that last one again)

If I want to make 1 mol NaCl: I take 22.90 grams of Na and 35.45 grams of Cl and I get 1 mol of NaCl

Let’s consider something else: CH4.

I need 1 carbon atom and 4 hydrogen atoms for every molecule of CH4.

If I want to make a dozen CH4: 12 carbon atoms and 48 (4×12) hydrogen atoms

If I want to make 1 mole CH4: 1 mole carbon atoms and 4 mole hydrogen atoms

or

1 mole (16 grams) CH4: 12 grams carbon and 4 (1×4) grams of hydrogen

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Does that help?

(It’s late at night, I’m going to reread this in the morning to see if it makes sense)

You explain that much better then prof who has been teaching for years. Thanks.

Mole problems?

Call Avogadro on: 6022–1023

The short answer is

*“a Mole is the number of molecules you need, to have a mass in grammes, of the same magnitude as the molecular mass in atomic mass units”*

it is basically the *ratio* between one gramme and one atomic mass unit.

There are 1mol of atomic mass units in a gramme.

Oddly enough, the atomic mass unit is not defined as ¹H, but as 1/12 of ¹²C.

There are other things that complicate the molecular mass, but you almost certainly don’t have to worry about them for a couple of years.

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