Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Question about mole

  1. Nov 25, 2011 #1
    Why is the amount of mole in gms. of an element the same as the its atomic mass. Is it just because $N_a X 1 u = 1$. Am i missing some simple reasoning behind this? Or was the carbon 12 taken exactly to make this valid?
     
  2. jcsd
  3. Nov 25, 2011 #2

    Borek

    User Avatar

    Staff: Mentor

    Simple answer - atomic unit was selected to make it happen.

    In a way you listed the same reason twice. Note what happens when you list units:

    [tex]N_a[\frac{atom}{mole}] \times u[\frac{g}{atom}] = 1[\frac{g}{mole}][/tex]
     
  4. Nov 26, 2011 #3

    morrobay

    User Avatar
    Gold Member

    You can also take a numerical example :

    1 atomic mass unit = 1.6605655 x 10-24 grams
    Once it is determined that 1 gram Hydrogen contains :
    1 g. H / 1.6605655 x 10-24 g = 6.02 x 1023
    1 mole H = Avogadro's number. Then it follows for 1 mole of any other element.
    Take 40 grams of Zr :
    40 g. Zr/ 40 * 1.660565 x 10-24 g. =
    40 g. Zr / 6.642 x 10-23 g = 6.02 x 10 23
     
  5. Dec 5, 2011 #4

    morrobay

    User Avatar
    Gold Member

    This should be 91 grams Zr :
    so : 91 grams Zr / 91 * 1.66 x 10 ^ -24 g
    = 91 g Zr / 15.1 x 10^-23 g = 6.02 x 10^23
     
    Last edited: Dec 5, 2011
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Question about mole
  1. Mole question (Replies: 1)

  2. Question about moles (Replies: 7)

Loading...