## Molar Mass and Molecular Mass Difference?

Sandra Kim 2B
Posts: 40
Joined: Wed Sep 30, 2020 9:50 pm

### Molar Mass and Molecular Mass Difference?

Was just wondering what's different between molar mass and molecular mass since the process for finding both seem to be practically identical (correct me if I'm wrong please I forgot everything about chem since hs). Or is this just not something I should worry about?

Mansi Solanki 1K
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### Re: Molar Mass and Molecular Mass Difference?

The molar mass is defined as the mass of a certain number of atoms, molecules, or compounds within one mole of the compound. It is measured in g/mol. The molecular mass is defined as the mass of one molecule. It is measured in amu.

Usually when you are calculating them for something like water, both the molar mass and molecular mass is the same (18.02 g/mol or 18.02 amu). For the most part, we use the molar mass in problems because they can then be used to convert to moles and relate different compounds and elements.

Posts: 39
Joined: Wed Sep 30, 2020 10:01 pm

### Re: Molar Mass and Molecular Mass Difference?

So are molecular mass and molar mass basically interchangeable?

Uyenvy Nguyen 3C
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Joined: Wed Sep 30, 2020 9:36 pm

### Re: Molar Mass and Molecular Mass Difference?

I think that they are the same numerically, but the units for molar mass is grams, while molecular mass is amu. They are a bit similar, so I can see how this can be confusing to think about.

Ansh Patel 3I
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Joined: Wed Sep 30, 2020 9:42 pm

### Re: Molar Mass and Molecular Mass Difference?

I believe that molar mass is the mass of one mole of a certain compound (C=12.01 g/mol), while molecular mass is the mass of a single molecule of a substance measured in amu (One molecule of H2O=18.02 amu).

Nico Medina
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Joined: Wed Sep 30, 2020 9:33 pm

### Re: Molar Mass and Molecular Mass Difference?

I believe that they are the same thing, as, by definiton, 1 amu = 1 g/mol. They will be the same for each respective element or compound, but as mentioned before, molar mass (g/mol) is useful for unit conversions. Hope this helps!

Lilly Catarozoli 1B
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### Re: Molar Mass and Molecular Mass Difference?

I believe they can be used interchangeably. It depends on what units you are trying to get for your answer.

Heidi Buri 2I
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Joined: Wed Sep 30, 2020 9:57 pm

### Re: Molar Mass and Molecular Mass Difference?

Usually, the molecular mass is thought of as the mass of particular molecules. There can be various molecular masses based on the different masses of isotopes. For example, the isotopes of carbon (carbon-12, carbon-13, and carbon-14) would all have different molecular masses due to their different isotopes. The molecular mass can also be the mass of any number of molecules. Different from the molecular mass, the molar mass is in terms of avagadro's number (6.022x10^23). Additionally , they differ in the units used. The units for molecular mass are atomic mass units while the units for molar mass are grams/moles.

DPatel_2L
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Joined: Wed Sep 30, 2020 9:41 pm

### Re: Molar Mass and Molecular Mass Difference?

They basically mean the same thing but have different units.

IanWheeler3F
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Joined: Wed Sep 30, 2020 9:49 pm

### Re: Molar Mass and Molecular Mass Difference?

Adding on to the isotope comment, the reason carbon's amu is 12.011 and not 12 is because the 12.011amu is the average of the masses of all carbon isotopes, so while most carbon is 12amu, there is a smaller fraction of carbon in the universe that weights more (13amu and 14amu) so after dividing the total mass of all the carbon atoms (all different masses depending on isotope) by the total carbon atoms present, you get a number slightly above 12

joshtully
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Joined: Wed Sep 30, 2020 9:36 pm

### Re: Molar Mass and Molecular Mass Difference?

What is an amu? I understand that it is a unit for molecular mass, but what does it stand for?

Bai Rong Lin 3I
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Joined: Wed Sep 30, 2020 9:54 pm

### Re: Molar Mass and Molecular Mass Difference?

when do the units matter or when do you know which unit do you use?

aashmi_agrawal_3j
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Joined: Wed Sep 30, 2020 9:39 pm

### Re: Molar Mass and Molecular Mass Difference?

They are basically the same but molar mass is measured in grams while molecular mass is measured in amu.

Moura Girgis 1D
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Joined: Wed Sep 30, 2020 10:00 pm

### Re: Molar Mass and Molecular Mass Difference?

How would you know which units to use per molar mass and which to use for molecular mass? Is it grams and moles for molar mass but formula units for molecular mass?

jessicaosuna_3E
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Joined: Wed Sep 30, 2020 9:51 pm

### Re: Molar Mass and Molecular Mass Difference?

Molar mass is specific to an atom. Molecular mass is the mass of the whole molecule, so that would be the molar masses of each individual atom within the molecule added up.

angelasavage
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Joined: Wed Sep 30, 2020 9:32 pm

### Re: Molar Mass and Molecular Mass Difference?

Moura Girgis 1D wrote:How would you know which units to use per molar mass and which to use for molecular mass? Is it grams and moles for molar mass but formula units for molecular mass?

The molar mass of an element (grams for 1 mol of the atoms of an element) is given via the periodic table. The molecular mass is in amu, and is the total mass of a molecule (multiplying the molar masses of each element by the numbers indicated in the molecular formula and then adding them up).

Kaiya_PT_1H
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### Re: Molar Mass and Molecular Mass Difference?

joshtully wrote:What is an amu? I understand that it is a unit for molecular mass, but what does it stand for?

amu means "atomic mass unit" which is a measurement based on the carbon atom: 1 amu = 1/12 the mass of an unbound carbon atom. https://www.thoughtco.com/definition-of ... amu-604366

Juliana Rosales 1J
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### Re: Molar Mass and Molecular Mass Difference?

They are the same thing but with different units. The units matter because then the answer will be wrong.

Ava_Basileo_2J
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Joined: Wed Sep 30, 2020 9:42 pm

### Re: Molar Mass and Molecular Mass Difference?

The difference is in the units. Simple:

1. molar mass is in grams per mol
2. molecular mass is in amu (atomic mass units)

Moura Girgis 1D
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Joined: Wed Sep 30, 2020 10:00 pm

### Re: Molar Mass and Molecular Mass Difference?

Those two are pretty interchangeable, they just require different units I think.