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Homework Help: A sample of a compound of cesium (Cs) and iodine (I) contain

  1. Jun 8, 2016 #1
    1. The problem statement, all variables and given/known data
    A sample of a compound of cesium (Cs) and iodine (I) contains 51.16g cesium and 48.84 g iodine, how many grams of cesium can be obtained from 85.5g of this compound?

    The attempt at a solution

    I don't really know where to begin. What I have tried was the following:
    51.16 g + 48.84 g = 100 g

    100 g - 85.5 g = 14.5 g

    51.16 g - 14.5 g = 36.66 g
    48.84 - 14.5 g = 34.34 g

    I'm pretty lost. The correct answer is 43.7g according to the answer key. How did they get that?
    thank you
  2. jcsd
  3. Jun 8, 2016 #2
    You have to use the law of definite proportions (Proust, 1797):

    The law of definite proportion, states that a chemical compound always contains exactly the same proportion of elements by mass.

    Therefore 100 g of compound contains 51.16g of Cesium. Use unitary method to figure out how much 85.5g of compound should contain.
  4. Jun 8, 2016 #3
    100 g Cesium / 51.16 g Cesium = 1.954

    85.5 g Cesium / 1.954 = 43.7 g

    I see it now, thank you for your help
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