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Homework Help: Finding the unknown atomic mass of element X

  1. Sep 11, 2012 #1
    1. The problem statement, all variables and given/known data
    Suppose a nameless element (X) was found to occur in three different substances (A, B and C). The relative molecular masses of A, B, and C were found to be 25.80, 43.70 and 83.50 respectively, compared to an assigned value of exactly 2.00 for H2. Subsequently, these substances were subjected to elemental analysis and were found to contain 92.3%, 81.7% and 85.6% of X respectively by mass.

    What is the (likely) relative atomic mass of X, on this scale

    3. The attempt at a solution
    What i did was i found the molecular mass of element X in each substance being 23.8g ,35.7g and 71.7g respective. But i'm not sure what to do after this point. Any hints?
  2. jcsd
  3. Sep 12, 2012 #2


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    Staff: Mentor

    What would be the mass, if you knew that substance A would contain exactly one atom of X per molecule? How would all allowed values (for 1, 2, 3, ... atoms per molecule) look like in that case?
    If that assumption gives results which do not fit to your other values, how can you fix it?
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