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Homework Help: Astronomy - Elemental composition of the Earth

  1. Jan 28, 2009 #1
    1. The problem statement, all variables and given/known data

    I am given a table with the abundances of atoms of different elements per 1000 Si atoms.
    The question wants me to tabulate the fraction of mass of the earth that each element, and different oxides contribute. But to do this I need to know how many Si atoms there are so I can calculate total amount of Si atoms. I could look this up, but I have a feeling I need to solve given the data, but there isn't any (or at least I think)

    2. Relevant equations

    The only data on silicon given is its molar mass, 28.09g/mol, its boiling and melting points (irrelevent) and its abundance (per 1000 Si atoms) - obviously 1000 - in both solar atmosphere and CI chondrites.

    I have the same data for every other element, and I need to know how to find the number of Si atoms in total. Once I find that I can finish the question. Any help?

    3. The attempt at a solution

    For comparison only, I looked up total Si by mass to be 15.2%, which is 9.07e26g -> 3.23e25 mol -> 1.95e49 atoms. Then as an example, taking that number and comparing it to Fe atoms, where the abundance is 890atoms (per 1000 of Si) I found Fe atoms = 1.73e49 -> 2.87e25 mol -> 1.6e24kg -> 26% mass of the earth

    So looks like I'd be on the right track -> if there was a way to find total number of Si atoms from the chart given. Any help please?
  2. jcsd
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