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Empiric formula question

  1. Mar 31, 2009 #1
    a matirial which weighs 1.235gram
    made of carbon oxigen and hydrogen
    and this material burned in oxigen
    which gives 3.425 gram of CO_2
    and 0.971 of H_2O ??
    what is the ampiric formula of the material
    ??
     
  2. jcsd
  3. Mar 31, 2009 #2

    Borek

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    1258 posts and you still don't know that you have to try by yourself before asking for help?
     
  4. Mar 31, 2009 #3

    tiny-tim

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    Hi transgalactic! :smile:

    What equations do you think are involved, and what constants do you need to know? :wink:
     
  5. Mar 31, 2009 #4

    symbolipoint

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    This one was reasonably difficult, but I found an answer. The trick is to account for both moles formula balance AND mass balance. (Or I should say, atoms balance AND mass balance). Initially, you have variables for the subscripts in the unknown C-H-O compound, and the way I proceeded, a coefficient variable for the reactant oxygen molecule and a coefficient 1 for the unknown compound. Like I say, I came up with what I believe is a very reasonable empirical formula result. I'd like to plainly state the result here, now, but doing so might not be acceptable at this state of progress on the forum.
     
  6. Apr 11, 2009 #5
    i have 0.077824106 moles of CO_2
    and 0.05389869 moles of H_2O

    what to do next??

    it not a whole numbers
    and i dont know how to build balancing equations for this
    ??
     
  7. Apr 11, 2009 #6

    symbolipoint

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    Well, so you have been thinking about and studying this exercise some more. Good.

    One of those values looks familar; the other I do not remember. I solved the problem on my own several days ago.

    See my last post on this topic. At first, you do not yet know the actual coefficients for the reactant compounds.

    The coefficients are unknow to start with, just as the subscripts for the atoms in the unknown compound. You need basic algebra-arithmetic skills. The decision on which final WHOLE numbers to find will come as one of your last steps. I initially found nonwhole values for one or more subscripts in the atoms of the compound also. The process was finished by finding a whole number factor which would keep all subscripts as extremely close to whole OR whole; and just good judgement.
     
  8. Apr 11, 2009 #7
    ok
    i have to find coefficient for C O H
    C=x
    O=y
    H=z
    x+0=0.077824106
    y+2=2*0.077824106+0.05389869
    z+0=2*0.05389869

    how to get whole cofficients from this decimal numbers
    ??
     
  9. Apr 16, 2009 #8
    hint:

    can you calculate the number of moles of CO2 you obtain?! If the products are CO2 and H2O only, then all the Carbon from the initial material have gone into CO2.

    so, if you have x mol of CO2 formed, then you should have had x mol of Carbon in the initial substance.

    Using this same logic you can find out for Hydrogen.

    but for Oxygen it is going to be a little bit tricky since the oxygen in the product comes from both the initial material and the oxygen gas supplied. you have find an alternative path!
     
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