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Homework Help: Calculating number of atoms in an alloy

  1. Sep 16, 2012 #1
    1. The problem statement, all variables and given/known data

    Germanium forms a substitutional solid solution with silicon. Compute the number of germanium atoms per cubic centimeter for a germanium-silicon alloy that contains 15 wt% Ge and 85 wt% Si. The densities of pure germanium and silicon are 5.32 and 2.33 g/cm3, respectively.

    2. Relevant equations

    I'm not sure on these. I will put the ones I think are applicable.

    C'1=(C1 A2)/((C1 A2)+(C2 A1))

    p (avg) = ((C'1 A1)+(C'2 A2))/((C'1 A1/p1)+(C'2 A2/p2))

    C = weight percent = wt%
    C' = atomic percent
    p = density
    A = atomic weight

    3. The attempt at a solution

    I can put the numbers in to get the atomic percents and the density of the alloy. I calculated 6.389 atomic% Ge and 93.611 atomic% Si. For the density of the alloy, I got 2.5445 g/cm3. The only problem is that I don't know how to get the number of Ge atoms in one cubic centimeter. How do I get there from where I am?
  2. jcsd
  3. Sep 20, 2012 #2
    No. of atoms of Ge
    =(2.5445/72.64)(6.02x10^23)= 2.11x10^22
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