chemistry help!

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Potassium has an atomic mass of 39.10amu. a sample of potassium is made up of isotopes potassium-39 (mass=38.964) and potassium-41(mass =40.962 amu). What percentage of the potassium sample is potassium-39? what percent of the sample is potassium-41?

  • chemistry help! -

    For a sample of K, with x grams of 39K and y grams of 41K the total mass will be

    38.964x + 40.962y

    Assuming a sample of 100g, we have

    38.964x + 40.962(100-x) = 39.10(100)
    x = 93.193

    39K is 93.193%
    41K = 6.807%

    check:

    38.964*.93193 + 40.962*.06807 = 39.10

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