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Homework Help: Differing between types of Mass

  1. Mar 12, 2016 #1
    • Please post this type of questions in the HW section using the template.
    Can someone please define and/or explain the difference between each of the following types of mass...
    1. Molar Mass
    2. Molecular Mass
    3. Formula Mass
    4. Atomic Mass
    I know that Molar Mass is the mass of one mole of a element or compound, and atomic mass is an average mass of all the isotopes, but the others are confusing me a little. And also, how do they relate to each other?
  2. jcsd
  3. Mar 12, 2016 #2


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    Staff: Mentor

    Have you tried to google them?
  4. Mar 12, 2016 #3
    I have googled them several times and it seems like some of these websites use them interchangeably. Specifically Molecular and Molar mass.
  5. Mar 12, 2016 #4


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    Google is very useful. For example only just used it to make sure whether I had got the real meaning of the expression "Black letter pedantry". I found examples but no definition, so I must not take the big risk of using it; however the search was still valuable as it led me to find the following rather witty and verbally virtuosistic verse by James Clerk Maxwell which will surely be new to many others.http://www.poetryfoundation.org/poem/175049

    Perhaps teachers' and our insistence on correct use of terminology makes us seem pedants, perhaps some of your teachers are pedants, but it is slightly amusing, perhaps slightly sad when, as quite often we meet here students who seem intent on making themselves pedants, sometimes with a degree of success.

    Anyway I do not think it is a good learning strategy to concentrate fiercely on memorising definitions out of context. On the average anyway, I suppose everyone can have his own technique, it might be what works for some.

    So relax - the terms mean just what they suggest. Read them in context and you should pick it up.

    So I guess molecular mass means the mass of a molecule. Unless it means the same as molar mass now I think of it perhaps it is also used that way*. I'm not worried. I would easily tell from context - the second would just be a number, the first instead would be a very tiny Number of kilograms. Which would be related to the molar mass by the Dalton number.
    * whilst I was writing you found this out.:approve:

    ''Formula mass' I'm guessing is the molecular mass of what we used to call with the 'empirical formula' best illustrated by an example. For example the glucose molecule (and many other hexose sugars) is C6H12O6. But if you just look at the proportion of atoms in its composition they correspond to CH2O which might be called the 'formula mass'. I have never met the term that I remember (a lot of these terms are imposed in schools before they are widespread outside, to where some of them never even make it). But if I did hear it I'm sure the meaning would be obvious from context.

    Last edited: Mar 12, 2016
  6. Mar 12, 2016 #5
    Ok. First off, I hope I don't sound like I'm worrying over these definitions, because I'm not even currently in a Chemistry class. I actually came across the terms molecular mass and formula mass in a Chemistry book I was reading that I found at the library (in the process of teaching myself chemistry), having already known about Atomic and Molar masses.

    I also just learned about the whole empirical formula thing which as you said, relates to formula mass. So would this mean that, for example, Acetylene C2H2and Benzene C6H6, having an empirical formula of CH, would have the same exact formula mass?
  7. Mar 13, 2016 #6


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    I think epenguin is wrong here. That is, his idea that the "formula mass" is a remnant of the times when we had to deal with empirical formulas can be quite right, and I agree with him formula mass is a rather obscure term you don't deal with often.

    No, they have the same empirical formula (CH), but different formula masses.

    Formula mass is the one calculated from the formula - and yes, if you feel like it is the same as molecular mass, you are right - it should be. That is, if you have a correct formula. If your formula is wrong, your formula mass differs from a molecular mass.
  8. Mar 13, 2016 #7
    Ok. Thanks for the help.
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