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Formula Weights

  1. Oct 18, 2004 #1
    Hello all

    I encountered the following problems:

    What is the formula weight of:

    a. potassium phosphate

    b. iron(III) oxide

    c. diphosphorous pentasulfide

    I know that the formula for (a) is K2S04. Hence I know there are 2K's 1 S and 4 O's. After obtaining the atomic masses, I sum them all up. The answer is 212.3 amu but I dont get this.

    Any help would be appreciated

    Thanks!
     
  2. jcsd
  3. Oct 19, 2004 #2
    K=39.098
    S=32.060
    O=15.999

    So:

    K2=78.197
    S=32.060
    O4=63.998

    So:

    K2SO4=174.254

    Do the same for the other ones.
     
  4. Oct 19, 2004 #3

    chem_tr

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    Science Advisor
    Gold Member

    The rest corresponds to two moles of water ions, as 2*18=36 grams/mol. So the total formula should be like K2SO4.2H2O.
     
    Last edited: Oct 19, 2004
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