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### Molar Mass

Posted: Sun Apr 08, 2018 9:24 pm
How do you calculate the molar mass of substance?

### Re: Molar Mass

Posted: Sun Apr 08, 2018 9:32 pm
You use the periodic table and look up the element's atomic mass. If you have a compound like h2o, you add up the atomic masses of 2(h) and 1 (o) to get the molar mass.

### Re: Molar Mass

Posted: Mon Apr 09, 2018 4:46 pm
Can someone please clarify when we use molar mass versus atomic mass?

### Re: Molar Mass

Posted: Mon Apr 09, 2018 6:12 pm
Atomic mass is measured via mass spectrometry. Molar mass is computed from the atomic weight. There are no units of measurement for atomic masses because these are relative masses meaning these are “unitless.” So the atomic mass is measured by calculating the mass of protons and neutrons. Whereas the Molar Mass is the grams per moles of a specific element. (or a specific compound by adding the molar mass of each element in the compound). The molar mass had units (g/moles) and the atomic mass is unitless.

### Re: Molar Mass

Posted: Mon Apr 09, 2018 6:20 pm
april is correct

### Re: Molar Mass

Posted: Thu Apr 12, 2018 11:57 pm
Atomic mass is the mass of an individual atom but molar mass is the mass of one mole of an atom.

### Re: Molar Mass

Posted: Sun Apr 15, 2018 12:35 pm
The correct units for molar mass is grams/mole, so you calculate the grams and that will be equal to one mole.

### Re: Molar Mass

Posted: Sun Apr 15, 2018 5:52 pm
The atomic mass does have units of mass. It can be in terms of "atomic mass unit" or even "kg" since this term refers to the mass of a single atom.

Unless we are talking atomic scale reactions (few tens and hundreds of atoms), we typically use molar mass since most everyday reactions concern with large quantities (moles) of chemicals in a reaction.

### Re: Molar Mass

Posted: Sun Apr 15, 2018 10:39 pm
It's also important to understand that Atomic mass is "unitless", while molar mass is grams/mol.

### Re: Molar Mass

Posted: Sun Apr 15, 2018 10:43 pm
I believe you add up all the weights of the elements. For example, in H20, you would multiply the weight of Hydrogen times two and add the weight of oxygen. I just noticed someone used H20 as an example previously, but this applies for other examples.