[mburt]

Hi guys,

As far as I can see, is the only difference between molecular and molar mass simply the units that they use?

For example:

Molar mass of oxygen = 15.999 g/mol

Molecular mass of oxygen = 15.999 u

Is this the only difference?

Thanks,

Michael

[XGen]

As far I know, that is the only difference.

[mburt]

Ok thanks. And beyond that I do understand the idea that the molecular mass (often called molecular weight, I think) is almost entirely made up of an atoms protons and neutrons. I'm also pretty sure that molar mass simply measures something's mass in terms of the amount of substance of it in moles, based on the convention of one mole of carbon-12 being 12g. (One mole of carbon itself being 12.0107g because of the weighted average of its isotopes).

If anyone has anything to add to this I would greatly appreciate it.

[Schrödinger]

Actually, molecular mass refers to the mass of one molecule (just one isotope). Molar mass refers to the mass of 1 mole of the substance (probably, you're thinking one is just an avogardro's factor away. But that is not the case). This one mole can contain isotopes and hence is an average.

read the wikipedia definitions of both for better clarity

[Borek]

Molecular mass of oxygen = 15.999 u

Atomic, molecular is at least twice that.

[mburt]

Thanks for your responses!