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Homework Help: Percent Composition & Finding Formula - Chemistry

  1. Mar 11, 2008 #1
    % Composition & Finding Formula - Chemistry

    50.0g of Sulphur is mixed with 100.0g of iron and heated strongly. When the reaction is complete 12.5g of iron remains. What is the formula of sulphide formed?

    duno where to start
  2. jcsd
  3. Mar 11, 2008 #2
    Convert everything to moles. Find the ratio of (moles sulphur consumed) to (moles iron consumed). That should give you the atomic ratio of sulphur to iron in the sulphide, which translates easily to a formula.

    In general, "convert everything to moles" is a good first step.
  4. Mar 11, 2008 #3
    hmmm kk well where i get lost is when i divide the moles.
    What i would do is divide big/small and get a decimal number but i dont knw how to convert that into a fraction
  5. Mar 11, 2008 #4
    Generally, if you did the problem correctly, a pretty obvious and easily recognizable ratio of small whole numbers will turn out. Just do it and then see.

    Admittedly, I always just used the ->frac command on my calculator.
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