[Ch3m]

Okay, I'm studying stoichiometry right now and I'm confused about this fact about moles:

"This means that 12 grams of ¹²C contain 6.022 x 10²³ atoms. It also means that a 12.01- gram sample of natural carbon contains 6.022 x 10²³ atoms."

This is sort of confusing but my text says that it is because the ratios of the masses are the same.

12g of natural Carbon/ 12.01grams (avg mass of Carbon-12,-13,-14)

12amu of Carbon 12/ 12.01 amu (avg mass of Carbon -12,-13,-14)

I guess the units cancel out but I'm still confused about how this works. I think it's mainly because of the different units, grams and amu. How are they both out of 12.01 when 1 amu= 1.66056x 10^-27 kg?
I just don't get how the grams and amu are equal for their avg masses.

1 amu = 1.6605387^-24 grams so how is the avg mass of the Carbons equal to both 12.01 amu and 12.01 grams? Confusing.. 

[Yggdrasil]

I think it's easier to think of the conversion as:

6.022x10²³ amu = 1g

So, for carbon-12, each atom of carbon 12 has a mass of 12 amu.  Therefore, 6.022x10²³ atoms of carbon-12 will have a mass of 12 g.

6.022x10²³ atoms * (12 amu/atom) * (1g/6.022x10²³ amu) = 12 g

For a normal sample of carbon (mixture of carbon-12, -13, and -14 isotopes), an atom of carbon has an average mass of 12.01 amu.  Therefore, one mole of carbon atoms will have a mass of 12.01 g.

I hope this clarifies things.

[Ch3m]

So there are exactly Avogadro's number of atoms in 1 ¹²C atom right? And there are exactly 12 grams in 1 ¹²C? There are also 12 amu in one atom of ¹²C That means:

(6.022 x 10²³atoms) x (12amu/ atom)= 12g

so 6.022x10^23 amu= 12g

but the thing I don't understand is how come 1 atom of ¹²C has masses of both 12 g and 12 amu?? Or is one of them a mole?

Thanks!

[Ch3m]

Oh I think I figured it out. Can someone please tell me if I'm right? Thanks in advance!

I think that one mole of ¹²C atoms is equal to 12 grams

while, on the other hand,

one atom of ¹²C is equal to 1 atomic mass unit (amu)

So in the periodic tables, the atmoic mass is measured as grams and are based on the mass of 1 mole of that element? They are not masses of atoms?

Thanks again!

[Yggdrasil]

One atom of ¹²C has a mass of 12 amu.
One mole of ¹²C has a mass of 12 grams.

This occurs because 6.022x10²³ amu = 1 gram.

[Ch3m]

Thanks! I think I get it now 

[Yggdrasil]

So in the periodic tables, the atmoic mass is measured as grams and are based on the mass of 1 mole of that element? They are not masses of atoms?

Also for more clarification:
The atomic mass represents both the mass of one atom of the element in amu and the mass of one mole of the element in grams.