Moles and Atomic Masses/Weights

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Rian Montagh 2K
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Joined: Fri Sep 28, 2018 12:15 am

Moles and Atomic Masses/Weights

Postby Rian Montagh 2K » Wed Oct 03, 2018 1:49 pm

I'm confused about why the atomic masses on the periodic table are the amount of grams in a mole of that element. In other words, I know that the atomic masses are the molar masses for elements, but I don't understand why they are. What do the atomic masses, (which are in amu?) have to do with the amount of grams in a mole? I'm just having a hard time seeing what the connection between these two pieces on info is, like why are they the same number?

pauline_le_3I
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Joined: Fri Sep 28, 2018 12:25 am

Re: Moles and Atomic Masses/Weights

Postby pauline_le_3I » Wed Oct 03, 2018 2:23 pm

Honestly, I've been wondering the same thing. I always thought that atomic mass and molar mass were interchangeable, and that molar mass was usually used for when you needed to calculate the mass of a compound. For example, the atomic mass of C (carbon) is 12, but the molar mass for the molecule CO2 (carbon dioxide) is 44. This probably isn't the whole reason, but thought I'd just add what I think is a distinct differentiation between the two.

Henry_Phan_4L
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Joined: Fri Sep 28, 2018 12:24 am

Re: Moles and Atomic Masses/Weights

Postby Henry_Phan_4L » Wed Oct 03, 2018 2:55 pm

The problem with the whole thing is that scientists used 12.000 grams of carbon (diamond) to figure out how many atoms were in a mole. Grams are the best standard that we have, so scientists used that as a baseline measurement. Professor Caram said that scientists are currently trying to use a sphere of silicon to determine an exact weight to atoms ratio.

Rian Montagh 2K
Posts: 60
Joined: Fri Sep 28, 2018 12:15 am

Re: Moles and Atomic Masses/Weights

Postby Rian Montagh 2K » Wed Oct 03, 2018 6:15 pm

Oh wait does it have to do with the fact that they used 12.000 g and the atomic mass for C is 12? So it's a 1:1 ratio...?

CateJensen3K
Posts: 32
Joined: Fri Sep 28, 2018 12:26 am

Re: Moles and Atomic Masses/Weights

Postby CateJensen3K » Wed Oct 03, 2018 6:51 pm

This was confusing for me as well. I looked back at the lecture notes and I have written down that the mass of sample (g) = number of moles (mol)*molar mass of element (g*mol^-1). I'm not sure if that helps or not?


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