Co2 and Octane problem

  1. I have the answer to the problem... only my problem is I can figure out how in the world world they came up with it. Here it is... I am sure it a pretty easy equation... only I don't get it!

    Calculate the mass of CO2 produced by the combustion of a tank of gasoline. Assume the mass of gasoline is 41.0 kg and that gasoline is pure octane (C8H18); 1 lb =454 g. Express your answer rounded to the nearest whole number. Do not include units with your answer.

    Correct answer: 278

    I have tried converting the 41.0kg in to grams and got .041g.
    I found the atomic mass of CO2 as 44 and X by 8 (research found Every molecule of octane makes eight molecules of CO2) which = 352.

    Also the Octane has a weight of 144.

    So I took .041g X (352/144)= 0.1

    WHat am I missing?
  2. jcsd
  3. chemisttree

    chemisttree 3,717
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    Find out what percentage of gasoline (isooctane) is carbon. Use atomic weight for carbon and hydrogen and formula wt for isooctane.
    This is the carbon source for all of the CO2 produced.

    The percent of gasoline that is carbon expressed in moles will equal to the moles of CO2.

    Also, recheck your formula wt. for isooctane... I get 114.
    And... I think the answer is wrong. I get 138 kg or 304 lb.
    Last edited: Mar 2, 2007
  4. GCT

    GCT 1,751
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    2 C8H18 + 25 O2 = 18 H2O + 16 CO2

    molecular mass of Octane is (8x12 + 18) grams/mole

    41000.0 grams Octane (1 mole/(114 grams)(16 moles CO2/2 moles Octane)(44 grams CO2/1 mole CO2)=127 kg

    Now we're all getting different answers. I used the stoichiometric equation however.
  5. chemisttree

    chemisttree 3,717
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    GCT has it right. The correct answer is 127 Kg or 278 lb.
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