## Molar Mass

Natalie_Martinez_1I
Posts: 30
Joined: Mon Feb 26, 2018 3:00 am

### Molar Mass

How do you calculate the molar mass of substance?

sylvie_1D
Posts: 31
Joined: Fri Apr 06, 2018 11:04 am

### Re: Molar Mass

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.

Isobel Tweedt 1E
Posts: 31
Joined: Fri Apr 06, 2018 11:05 am

### Re: Molar Mass

Can someone please clarify when we use molar mass versus atomic mass?

april_bussey_1C
Posts: 30
Joined: Fri Apr 06, 2018 11:02 am

### Re: Molar Mass

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.

kimberlysanchez-1E
Posts: 30
Joined: Tue Nov 14, 2017 3:01 am

### Re: Molar Mass

april is correct

AlyssaRivera
Posts: 29
Joined: Fri Apr 06, 2018 11:04 am

### Re: Molar Mass

Atomic mass is the mass of an individual atom but molar mass is the mass of one mole of an atom.

juliaschreib1A
Posts: 29
Joined: Fri Sep 29, 2017 7:06 am

### Re: Molar Mass

The correct units for molar mass is grams/mole, so you calculate the grams and that will be equal to one mole.

Chem_Mod
Posts: 18016
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 418 times

### Re: Molar Mass

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.

Elijah E 1C
Posts: 15
Joined: Fri Apr 06, 2018 11:02 am

### Re: Molar Mass

It's also important to understand that Atomic mass is "unitless", while molar mass is grams/mol.

Jennifer 1G
Posts: 29
Joined: Wed Nov 15, 2017 3:03 am

### Re: Molar Mass

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.