Summary - Molar Mass

So that's why we usually refer to the atomic mass of atoms, or the molecular mass of molecules, or the formula mass of ionic compounds as the molar mass. As we've shown here, calculating molar mass is actually pretty easy:

  • to calculate the molar mass of an atom, look up its atomic mass in a table. 
  • to calculate the molar mass of a formula, whether ionic or a true molecular substance, add up the atomic masses of all the atoms in the formula unit.
  • The mole as it was defined here should actually be called the gram-mole, since it is defined as "enough atoms to equal the atomic mass in grams." At one time chemical engineers sometimes used a pound-mole, which would be defined as "enough atoms to equal the atomic mass in pounds." The "enough" in these two different definitions would be a different number, but the concept is the same.

    The abbreviation for mole is mol. Using this is not exactly going to save you a lot of ink! Be careful not to use m as an abbreviation. m usually means meters, though in chemistry it can also mean molality, which is not the same thing as moles.

    If you think that you've got this, then try these examples, and check your answers against what the calculator gives.

    1. KCl 
    2. Na2O 
    3. Li2SO4 
    4. Ba(OH)2 
    5. (NH4)3PO4 
    6. (NH4)2C2O4.H2O 
    7. SrCl2.6H2O 

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    Copyright © 1998 - 2008 David Dice

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