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    Hi Guys,

    I'm wondering if someone could help me with this question i have. i am currently studying an open university course which i am finding pretty tricky to manage with a full time job. one question i have been stuck on for far to long is this one....




    Calculate the stoichiometric dry flue gas analysis for a fuel oil, which has an ultimate analysis of 83% carbon and 17% hydrogen (bymass), when it is burnt with air.



    Could someone let know how to do this as the course notes i have and my tutor are extermely unhelpful.

    Cheers

    Mark
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    presumably, they want you to come up with an empirical formula. Do you know how to do that from the % C and H ?
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    sorry, i really am not sure, i guess thats what they are looking for.... i dont know how to do this from the % C and H. im sorry thats not much help but the question is that vague.
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    ok, if you have the percentage by mass of each element you can derive the empirical forumula of the compound.

    You know that 83% of the mass is C and 17% is H. But C atoms are heavier than H atoms, so you have to allow for this (since your empirical formula is the ratios of the number of atoms of each element in a compound).

    So, just divide the % by the atomic mass of that element. That number will give you the ratio of each element in the compound (which is the empirical formula)

    So try that, and I shall see if I agree with your numbers.
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    ok, maybe im abit stupid here but how do i know what the atomic mass is of each element?
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    have you got a periodic table handy? There should be two numbers in the square for each element. The smaller one is the atomic number (the number of protons/electrons) and the larger one is the relative atomic mass. It's that larger one you want.

    What level is this course you're doing with OU? You need to get to know the periodic table well. Make it your friend. It wil repay you amply! It is absolutely fundamental to understanding chemistry.
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    sorry i dont but i have just looked on the net, am i right in saying Carbon is 12.011 and Hydrogen is 1.0094???
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    (Original post by markyb24)
    sorry i dont but i have just looked on the net, am i right in saying Carbon is 12.011 and Hydrogen is 1.0094???
    correct. for your purposes, 12 and 1 will do (see my edit above)
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    If you don't know the atomic masses of Hydrogen and carbon off by heart already you're probably going to find the question impossibly hard....
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    ok so it will be 83 / 12 = 6.92 for C and 17 / 1 = 17 for H giving a ratio of 6.92:17???
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    its an OU course in Energy Management. I'm a property manager for a large tele comms company and this, to be fair is completely over my head!! i havent done chemistry since i was 16, and it was never one of my strong points.....
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    (Original post by markyb24)
    ok so it will be 83 / 12 = 6.92 for C and 17 / 1 = 17 for H giving a ratio of 6.92:17???
    correct. Round them for the ratios and you have 7 for C and 17 for H. So your empirical formula is C_7H_{17}

    that means the actual molecular formula is (C_7H_{17})_n (where n is a whole number)
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    Right, i see now..... thanks. so that all the question is asking for??? honestly, this is something i never thought id be doing for an energy management qualification!!
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    well, I agree. It seems like an odd question to be asking. Are you sure you have quoted it right? maybe if you can reproduce the question word for word here it might help?
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    this is the question from the 1st post, this is all it gives me..... my tutor has just told me to scan through the course notes which i have done around 12 times but doesnt make any sense to me.

    Calculate the stoichiometric dry flue gas analysis for a fuel oil, which has an ultimate analysis of 83% carbon and 17% hydrogen (bymass), when it is burnt with air.
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    that cant possibly be the question they set you, how could you calculate and analysis?
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    Hi Amscared - honestly this is all i have to work from. is there anyway i can possibly post the paper on here for you to see what i have to contend with.....
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    Guys, this is my next question i am struggling with. once again, any help would be greatly appreciated.....

    A boiler burning heavy fuel oil has a flue gas CO2 content (dry, by volume) of 13%, and a flue gas temperature of 300oC. Find the oxygen content, excess combustion air and percentage flue gas losses.
    Explain why the flue gas losses are not the total losses from the system.


    thanks
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    (Original post by markyb24)
    Guys, this is my next question i am struggling with. once again, any help would be greatly appreciated.....

    A boiler burning heavy fuel oil has a flue gas CO2 content (dry, by volume) of 13%, and a flue gas temperature of 300oC. Find the oxygen content, excess combustion air and percentage flue gas losses.
    Explain why the flue gas losses are not the total losses from the system.


    thanks
    Hi there I am currently undertaking this assignment, and was wondering if you had any advice on how to answer this question. Very rusty on the old chemistry.


    thanks
 
 
 
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