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Homework Help: Find the Formula of compound X

  1. Aug 11, 2010 #1
    1. The problem statement, all variables and given/known data
    When 1.11 g of a compound X is completely burnt,1.98 g of carbon dioxide and 0.81 g of water were formed. Which of the following could be X?

    A. CH[tex]_{3}[/tex]CH[tex]_{2}[/tex]CH[tex]_{3}[/tex]
    B. CH[tex]_{3}[/tex]CH[tex]_{2}[/tex]COOH

    3. The attempt at a solution

    I tried

    C[tex]_{x}[/tex]H[tex]_{y}[/tex] + {x+[tex]\frac{y}{4}[/tex]}O[tex]_{2}[/tex] [tex]\rightarrow[/tex]
    XC0[tex]_{2}[/tex] + [tex]\frac{y}{2}[/tex]H[tex]_{2}[/tex]O

    but how about the oxygen atom(s) within compound X?

    How can I form a balanced equation for X containing O?

    Sorry about the equations and formulae... can't get the subscripts in the right positions.
    Last edited: Aug 11, 2010
  2. jcsd
  3. Aug 11, 2010 #2


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    Science Advisor

    The only things in the product that you can be absolutely sure come from the reactant is the carbon and hydrogen. So, from the water and CO2, calculate how many moles of C and H you had to begin with. What's the mass of this amount of carbon and hydrogen - is it enough to account for all of the 1.11 g you had to begin with?
  4. Aug 12, 2010 #3
    Got it. Useful hint.Thanks. Answer's B. :smile:
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