Why does carbon have molar mass 12.011g/mol?  [ENDORSED]

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Mei Blundell_1J
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Why does carbon have molar mass 12.011g/mol?

Postby Mei Blundell_1J » Fri Apr 06, 2018 4:42 pm

Hello!
The definition of a mole is the number of atoms in exactly 12 g of carbon, and it follows that the mass of 1 mole of carbon should be exactly 12g. So, I'm confused about why the molar mass of carbon is 12.011 g/mol. Could anyone help explain this to me?
Thanks,
Mei

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Re: Why does carbon have molar mass 12.011g/mol?  [ENDORSED]

Postby Chem_Mod » Sat Apr 07, 2018 9:12 am

You omitted a key part of the definition which also explains the difference.

The mass of 1 mole of carbon should be exactly 12 g of carbon-12.

There are different isotopes for elements.

The definition is based on the mole of carbon-12, but in a carbon sample, you will have a small percentage of carbon-13, making it 12.011 g.mol-1.
Good question!


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