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Homework Help: Molecular formula of combustion?

  1. Aug 21, 2011 #1
    complete combustion of 1.1g of a compound of C,H and O gives 2.2g of CO2 and 0.9g of H2O.
    The compound has a relative molar mass close to 130.
    Find the molecular formula and true molar mass?

    dont even no where to begin
  2. jcsd
  3. Aug 22, 2011 #2


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    Staff: Mentor

    Google "finding empirical formula".
  4. Aug 24, 2011 #3
    so you got the masses of the products right? 2.2g for CO2 and 0.9g for H2O.

    you knowthe molar masses of those elements by looking at the periodic table

    for example, the moalr mass of CO2 is (approximately because of rounding)= 12+16+16=44g/mol

    do the same thing to get the molar mass of H2O (hydrogen is 1) to get the H2O moles

    what has me confused though is that it doesnt appear to obbey the conservation of mass law, how can you have 1.1g of something and get 2.2g+0.9g of something else???

    maybe im just reading wrong...

    then divide the mass of the substances by the molar massses, to get number of moles, so 2.2/44=0.05 moles of CO2
  5. Aug 25, 2011 #4


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    Staff: Mentor

    Combustion means there is a source of oxygen.

    Please pay attention to what and how you write, don't ignore capital letters and watch for typos.
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