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Homework Help: Percent abundance of isotopes

  1. Sep 8, 2009 #1
    i am trying to figure out the percent abundance of two isotopes. i know how to set up the problem but i dont know how to find the weight of each isotopes. here is the problem:

    Cerium (58Ce) has two commonly occuring isotopes, 140Ce and 142Ce. what is the approximate percent abundance of 140Ce?
  2. jcsd
  3. Sep 8, 2009 #2


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    140Ce means that the isotope has an atomic mass of (approximately) 140 amu.
  4. Sep 8, 2009 #3


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    What is the given mass of natural cerium? The mass should be a weighted average based on the isotopic abundances and the mass of each isotope. For two isotopes, it's pretty simple.
  5. Sep 8, 2009 #4
    Hi kceddis-
    There are an abundance of tables on isotopes and nuclear data at LBL (Lawrence Berkeley Laboratory) follow your google search by site:lbl.gov

    Here is a table for finding atomic masses of all the isotopes.
    In this case, type in the elemend Z# or symbol, and it gives the atomic masses of all the isotopes of that element. The masses are given in micro atomic units, so you have to divide by 1 million. For example Ce-140 is shown as 139905439 which is actually 139.905439 amu's (atomic mass units).
    I hope this helps
    Bob S
    Last edited by a moderator: Apr 24, 2017
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